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LM2575-D

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LM2575

1.0 A, Adjustable OutputVoltage, Step-DownSwitching Regulator

The LM2575 series of regulators are monolithic integrated circuitsideally suited for easy and convenient design of a step−downswitching regulator (buck converter). All circuits of this series arecapable of driving a 1.0 A load with excellent line and load regulation.These devices are available in fixed output voltages of 3.3 V, 5.0 V,12 V, 15 V, and an adjustable output version.

These regulators were designed to minimize the number of externalcomponents to simplify the power supply design. Standard series ofinductors optimized for use with the LM2575 are offered by severaldifferent inductor manufacturers.

Since the LM2575 converter is a switch−mode power supply, itsefficiency is significantly higher in comparison with popularthree−terminal linear regulators, especially with higher input voltages.In many cases, the power dissipated by the LM2575 regulator is solow, that no heatsink is required or its size could be reduceddramatically.

The LM2575 features include a guaranteed ±4% tolerance on outputvoltage within specified input voltages and output load conditions, and±10% on the oscillator frequency (±2% over 0°C to 125°C). Externalshutdown is included, featuring 80 mA typical standby current. Theoutput switch includes cycle−by−cycle current limiting, as well asthermal shutdown for full protection under fault conditions.

Features

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15TO−220TV SUFFIXCASE 314B

Heatsink surface connected to Pin 3

15TO−220T SUFFIXCASE 314D

•3.3 V, 5.0 V, 12 V, 15 V, and Adjustable Output Versions

•Adjustable Version Output Voltage Range of 1.23 V to 37 V ±4%••••••••••••••••

Maximum Over Line and Load ConditionsGuaranteed 1.0 A Output Current

Wide Input Voltage Range: 4.75 V to 40 VRequires Only 4 External Components52 kHz Fixed Frequency Internal Oscillator

TTL Shutdown Capability, Low Power Standby ModeHigh Efficiency

Uses Readily Available Standard Inductors

Thermal Shutdown and Current Limit ProtectionMoisture Sensitivity Level (MSL) Equals 1Pb−Free Packages are Available*

1.2.3.4.5.Vin

OutputGroundFeedbackON/OFF1

5D2PAKD2T SUFFIXCASE 936A

Heatsink surface (shown as terminal 6 incase outline drawing) is connected to Pin 3

ORDERING INFORMATION

See detailed ordering and shipping information in the packagedimensions section on page 25 of this data sheet.

Applications

Simple and High−Efficiency Step−Down (Buck) RegulatorsEfficient Pre−Regulator for Linear RegulatorsOn−Card Switching Regulators

Positive to Negative Converters (Buck−Boost)Negative Step−Up Converters

Power Supply for Battery Chargers

DEVICE MARKING INFORMATION

See general marking information in the device markingsection on page 26 of this data sheet.

*For additional information on our Pb−Free strategy and soldering details, pleasedownload the ON Semiconductor Soldering and Mounting TechniquesReference Manual, SOLDERRM/D.

July, 2008 − Rev. 9

Publication Order Number:

LM2575/D

LM2575

Typical Application (Fixed Output Voltage Versions)

Feedback7.0 V - 40 VUnregulated DC Input

+VinCin100 mF13GND5LM25754Output2ON/OFFL1330 mHD11N5819Cout330 mF5.0 V Regulated Output 1.0 A Load

Representative Block Diagram and Typical Application

UnregulatedDC InputCin4FeedbackR2Fixed GainError AmplifierComparatorFreqShift18 kHz52 kHzOscillatorCurrentLimit+Vin1ON/OFF53.1 V InternalRegulatorON/OFFOutputVoltage Versions3.3 V5.0 V12 V15 VFor adjustable versionR1 = open, R2 = 0 WR2(W)1.7 k3.1 k8.84 k11.3 kR11.0 kDriverLatchOutput1.0 AmpSwitchResetThermalShutdown2GND3D1L1RegulatedOutputVoutCoutLoad1.235 VBand-GapReferenceThis device contains 162 active transistors.Figure 1. Block Diagram and Typical Application

ABSOLUTE MAXIMUM RATINGS (Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.)

Rating

Maximum Supply VoltageON/OFF Pin Input VoltageOutput Voltage to Ground (Steady−State)

Power Dissipation

Case 314B and 314D (TO−220, 5−Lead)Thermal Resistance, Junction−to−AmbientThermal Resistance, Junction−to−CaseCase 936A (D2PAK)

Thermal Resistance, Junction−to−Ambient (Figure 34)Thermal Resistance, Junction−to−CaseStorage Temperature Range

Minimum ESD Rating (Human Body Model: C = 100 pF, R = 1.5 kW)Lead Temperature (Soldering, 10 s)Maximum Junction Temperature

SymbolVin−−PDRqJARqJCPDRqJARqJCTstg−−TJ

Value45

−0.3 V ≤ V ≤ +Vin

−1.0Internally Limited

655.0

Internally Limited

705.0−65 to +150

2.0260150

UnitVVVW°C/W°C/WW°C/W°C/W°CkV°C°C

Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above theRecommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affectdevice reliability.

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LM2575

OPERATING RATINGS (Operating Ratings indicate conditions for which the device is intended to be functional, but do not guaranteespecific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.)

Rating

Operating Junction Temperature RangeSupply Voltage

SymbolTJVin

Value−40 to +125

Unit°CV

SYSTEM PARAMETERS ([Note 1] Test Circuit Figure 14)

ELECTRICAL CHARACTERISTICS (Unless otherwise specified, Vin = 12 V for the 3.3 V, 5.0 V, and Adjustable version, Vin = 25 Vfor the 12 V version, and Vin = 30 V for the 15 V version. ILoad = 200 mA. For typical values TJ = 25°C, for min/max values TJ is theoperating junction temperature range that applies [Note 2], unless otherwise noted.)

Characteristics

LM2575−3.3 (Note 1 Test Circuit Figure 14)

Output Voltage (Vin = 12 V, ILoad = 0.2 A, TJ = 25°C)Output Voltage (4.75 V ≤ Vin ≤ 40 V, 0.2 A ≤ ILoad ≤ 1.0 A)TJ = 25°C

TJ = −40 to +125°C

Efficiency (Vin = 12 V, ILoad = 1.0 A)LM2575−5 ([Note 1] Test Circuit Figure 14)

Output Voltage (Vin = 12 V, ILoad = 0.2 A, TJ = 25°C)Output Voltage (8.0 V ≤ Vin ≤ 40 V, 0.2 A ≤ ILoad ≤ 1.0 A)TJ = 25°C

TJ = −40 to +125°C

Efficiency (Vin = 12 V, ILoad = 1.0 A)LM2575−12 (Note 1 Test Circuit Figure 14)

Output Voltage (Vin = 25 V, ILoad = 0.2 A, TJ = 25°C)Output Voltage (15 V ≤ Vin ≤ 40 V, 0.2 A ≤ ILoad ≤ 1.0 A)TJ = 25°C

TJ = −40 to +125°C

Efficiency (Vin = 15V, ILoad = 1.0 A)LM2575−15 (Note 1 Test Circuit Figure 14)

Output Voltage (Vin = 30 V, ILoad = 0.2 A, TJ = 25°C)Output Voltage (18 V ≤ Vin ≤ 40 V, 0.2 A ≤ ILoad ≤ 1.0 A)TJ = 25°C

TJ = −40 to +125°C

Efficiency (Vin = 18 V, ILoad = 1.0 A)

LM2575 ADJUSTABLE VERSION (Note 1 Test Circuit Figure 14)Feedback Voltage (Vin = 12 V, ILoad = 0.2 A, Vout = 5.0 V, TJ = 25°C)Feedback Voltage (8.0 V ≤ Vin ≤ 40 V, 0.2 A ≤ ILoad ≤ 1.0 A, Vout = 5.0 V)TJ = 25°C

TJ = −40 to +125°C

Efficiency (Vin = 12 V, ILoad = 1.0 A, Vout = 5.0 V)

VFBVFB

1.2171.1931.18−

1.231.23−77

1.2431.2671.28−

%VV

VoutVout

14.714.414.25−

1515−88

15.315.615.75−

%VV

VoutVout

11.7611.5211.4−

1212−88

12.2412.4812.6−

%VV

VoutVout

4.94.84.75−

5.05.0−77

5.15.25.25−

%VV

VoutVout

3.2343.1683.135−

3.33.3−75

3.3663.4323.465−

%VV

Symbol

Min

Typ

Max

Unit

1.External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance.When the LM2575 is used as shown in the Figure 14 test circuit, system performance will be as shown in system parameters section.2.Tested junction temperature range for the LM2575: Tlow = −40°C Thigh = +125°C

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LM2575

DEVICE PARAMETERS

Characteristics

ALL OUTPUT VOLTAGE VERSIONS

Feedback Bias Current (Vout = 5.0 V Adjustable Version Only)TJ = 25°C

TJ = −40 to +125°COscillator Frequency Note 3TJ = 25°C

TJ = 0 to +125°CTJ = −40 to +125°C

Saturation Voltage (Iout = 1.0 A Note 4)TJ = 25°C

TJ = −40 to +125°CMax Duty Cycle (“on”) Note 5

Current Limit (Peak Current Notes 4 and 3)TJ = 25°C

TJ = −40 to +125°C

Output Leakage Current Notes 6 and 7, TJ = 25°COutput = 0 VOutput = −1.0 VQuiescent Current Note 6TJ = 25°C

TJ = −40 to +125°C

Standby Quiescent Current (ON/OFF Pin = 5.0 V (“off”))TJ = 25°C

TJ = −40 to +125°C

ON/OFF Pin Logic Input Level (Test Circuit Figure 14)Vout = 0 VTJ = 25°C

TJ = −40 to +125°C

Vout = Nominal Output VoltageTJ = 25°C

TJ = −40 to +125°C

ON/OFF Pin Input Current (Test Circuit Figure 14)ON/OFF Pin = 5.0 V (“off”), TJ = 25°CON/OFF Pin = 0 V (“on”), TJ = 25°C

−−−4742−−941.71.4−−−−15−

25−52−−1.0−982.3−0.86.05.0−80−

100200

kHz

−5863

1.21.3−3.03.2

2.020

9.011200400

mA%A

Symbol

Min

Typ

Max

Unit

fosc

Vsat

DCICL

Istby

VIH

2.22.4−−−−

1.4−1.2−150

−−1.00.8

IIHIIL

305.0

VIL

3.The oscillator frequency reduces to approximately 18 kHz in the event of an output short or an overload which causes the regulated outputvoltage to drop approximately 40% from the nominal output voltage. This self protection feature lowers the average dissipation of the IC bylowering the minimum duty cycle from 5% down to approximately 2%.

4.Output (Pin 2) sourcing current. No diode, inductor or capacitor connected to output pin.5.Feedback (Pin 4) removed from output and connected to 0 V.

6.Feedback (Pin 4) removed from output and connected to +12 V for the Adjustable, 3.3 V, and 5.0 V versions, and +25 V for the 12 V and15 V versions, to force the output transistor “off”.7.Vin = 40 V.

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LM2575

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 14)

0.6Vout, OUTPUT VOLTAGE CHANGE (%)0.40.20-0.2-0.4-0.6-50-250255075100125Vout, OUTPUT VOLTAGE CHANGE (%)Vin = 20 VILoad = 200 mANormalized atTJ = 25°C1.00.80.60.40.20-0.205.010152012 V and 15 V25303540ILoad = 200 mATJ = 25°C3.3 V, 5.0 V and AdjTJ, JUNCTION TEMPERATURE (°C)Vin, INPUT VOLTAGE (V)

Figure 2. Normalized Output VoltageFigure 3. Line Regulation

1.2Vsat, SATURATION VOLTAGE (V)1.11.00.90.80.70.60.50.40

125°C25°C-40°CIO, OUTPUT CURRENT (A)3.02.52.01.51.00.50.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0-50

Vin = 25 V-25

100

125

0.10.2

SWITCH CURRENT (A)

TJ, JUNCTION TEMPERATURE (°C)

Figure 4. Switch Saturation VoltageFigure 5. Current Limit

2.0INPUT-OUTPUT DIFFERENTIAL (V)ILoad = 1.0 AIQ, QUIESCENT CURRENT (mA)1.81.61.41.21.00.80.60.4-50-250255075100125ILoad = 200 mADVout = 5%Rind = 0.2 W2018161412108.06.04.005.01015202530ILoad = 200 mAILoad = 1.0 AVout = 5.0 VMeasured atGround PinTJ = 25°C3540TJ, JUNCTION TEMPERATURE (°C)Vin, INPUT VOLTAGE (V)

Figure 6. Dropout VoltageFigure 7. Quiescent Current

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LM2575

Istby, STANDBY QUIESCENT CURRENT ( μ A)TJ = 25°CIstby, STANDBY QUIESCENT CURRENT ( μ A)1201008060402000

5.0

120100806040200-50-250255075100125Vin = 12 VVON/OFF = 5.0 VVin, INPUT VOLTAGE (V)TJ, JUNCTION TEMPERATURE (°C)

Figure 8. Standby Quiescent CurrentFigure 9. Standby Quiescent Current

2.00-2.0-4.0-6.0-8.0-10-50-250255075100125IFB, FEEDBACK PIN CURRENT (nA)NORMALIZED FREQUENCY (%)Vin = 12 VNormalized at 25°C40AdjustableVersion Only200-20-40-50-250255075100125TJ, JUNCTION TEMPERATURE (°C)TJ, JUNCTION TEMPERATURE (°C)

Figure 10. Oscillator FrequencyFigure 11. Feedback Pin Current

OUTPUTVOLTAGE(PIN 2)

10 V0

ILoad, LOAD CURRENT (A)Vout, OUTPUT VOLTAGE CHANGE (mV)1000OUTPUT1.0 ACURRENT(PIN 2)0INDUCTORCURRENT

-1001.0 A0.5 A

1.00.50OUTPUT20 mVRIPPLE/DIVVOLTAGE

5.0 ms/DIV100 ms/DIV

Figure 12. Switching WaveformsFigure 13. Load Transient Response

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LM2575

5.0 Output Voltage Versions

FeedbackVin+13Cin100 mF/50 V4LM2575−5OutputGND52ON/OFFD11N5819Cout330 mF/16 VLoadL1330 mHVoutRegulatedOutputVinUnregulatedDC Input8.0 V - 40 V-Adjustable Output Voltage Versions

FeedbackVin+13Cin100 mF/50 VLM2575Adjustable4Output2ON/OFFD11N5819Cout330 mF/16 VR2LoadR1L1330 mHVoutRegulatedOutputUnregulatedDC Input8.0 V - 40 VGND5-Vout+VR2+R1

ref

ǒ1) R2ǓR1 1ref

ǒǓ

VoutV

Where Vref = 1.23 V, R1

between 1.0 kW and 5.0 kW

Figure 14. Typical Test Circuit

PCB LAYOUT GUIDELINES

As in any switching regulator, the layout of the printedcircuit board is very important. Rapidly switching currentsassociated with wiring inductance, stray capacitance andparasitic inductance of the printed circuit board traces cangenerate voltage transients which can generateelectromagnetic interferences (EMI) and affect the desiredoperation. As indicated in the Figure 14, to minimizeinductance and ground loops, the length of the leadsindicated by heavy lines should be kept as short as possible.For best results, single−point grounding (as indicated) orground plane construction should be used.

On the other hand, the PCB area connected to the Pin 2(emitter of the internal switch) of the LM2575 should bekept to a minimum in order to minimize coupling to sensitivecircuitry.

Another sensitive part of the circuit is the feedback. It isimportant to keep the sensitive feedback wiring short. Toassure this, physically locate the programming resistors nearto the regulator, when using the adjustable version of theLM2575 regulator.

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LM2575

PIN FUNCTION DESCRIPTION

Pin1

SymbolVin

Description (Refer to Figure 1)

This pin is the positive input supply for the LM2575 step−down switching regulator. In order to minimizevoltage transients and to supply the switching currents needed by the regulator, a suitable input bypasscapacitor must be present (Cin in Figure 1).

This is the emitter of the internal switch. The saturation voltage Vsat of this output switch is typically 1.0 V.It should be kept in mind that the PCB area connected to this pin should be kept to a minimum in order tominimize coupling to sensitive circuitry.

Circuit ground pin. See the information about the printed circuit board layout.

This pin senses regulated output voltage to complete the feedback loop. The signal is divided by the

internal resistor divider network R2, R1 and applied to the non−inverting input of the internal error amplifier.In the Adjustable version of the LM2575 switching regulator this pin is the direct input of the error amplifierand the resistor network R2, R1 is connected externally to allow programming of the output voltage.It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the totalinput supply current to approximately 80 mA. The input threshold voltage is typically 1.4 V. Applying avoltage above this value (up to +Vin) shuts the regulator off. If the voltage applied to this pin is lower than1.4 V or if this pin is connected to ground, the regulator will be in the “on” condition.

2Output

GNDFeedback

5ON/OFFDESIGN PROCEDURE

Buck Converter Basics

The LM2575 is a “Buck” or Step−Down Converter whichis the most elementary forward−mode converter. Its basicschematic can be seen in Figure 15.

The operation of this regulator topology has two distincttime periods. The first one occurs when the series switch ison, the input voltage is connected to the input of the inductor.The output of the inductor is the output voltage, and therectifier (or catch diode) is reverse biased. During thisperiod, since there is a constant voltage source connectedacross the inductor, the inductor current begins to linearlyramp upwards, as described by the following equation:

IL(on)+

current loop. This removes the stored energy from theinductor.

The inductor current during this time is:

ǒVoutVDǓtoff

LL(off)

This period ends when the power switch is once againturned on. Regulation of the converter is accomplished byvarying the duty cycle of the power switch. It is possible todescribe the duty cycle as follows:

d+on, where T is the period of switching.

TǒVinVoutǓton

LFor the buck converter with ideal components, the dutycycle can also be described as:

Vd+outVin

During this “on” period, energy is stored within the corematerial in the form of magnetic flux. If the inductor isproperly designed, there is sufficient energy stored to carrythe requirements of the load during the “off” period.

PowerSwitchLFigure 16 shows the buck converter idealized waveformsof the catch diode voltage and the inductor current.

VoutVinD1CoutRLoad

Figure 15. Basic Buck Converter

The next period is the “off” period of the power switch.When the power switch turns off, the voltage across theinductor reverses its polarity and is clamped at one diodevoltage drop below ground by catch dioded. Current nowflows through the catch diode thus maintaining the load

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LM2575

Von(SW)Diode VoltagePowerSwitchOffPowerSwitchOnPowerSwitchOffPowerSwitchOnTimeInductor CurrentVD(FWD)IpkILoad(AV)IminDiodePowerSwitchDiodePowerSwitchTimeFigure 16. Buck Converter Idealized Waveforms

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LM2575

Procedure (Fixed Output Voltage Version) In order to simplify the switching regulator design, a step−by−step design

procedure and example is provided.

ProcedureGiven Parameters:Vout = Regulated Output Voltage (3.3 V, 5.0 V, 12 V or 15 V)Vin(max) = Maximum DC Input VoltageILoad(max) = Maximum Load Current1.Controller IC SelectionAccording to the required input voltage, output voltage and current, select the appropriate type of the controller IC output voltage version.2.Input Capacitor Selection (Cin)To prevent large voltage transients from appearing at the input and for stable operation of the converter, an aluminium or tantalum electrolytic bypass capacitor is needed between the input pin +Vin and ground pin GND. This capacitor should be located close to the IC using short leads. This capacitor should have a low ESR (Equivalent Series Resistance) value.3.Catch Diode Selection (D1)A.Since the diode maximum peak current exceeds the regulator maximum load current the catch diode current rating must be at least 1.2 times greater than the maximum load current. For a robust design the diode should have a current rating equal to the maximum current limit of the LM2575 to be able to withstand a continuous output shortB.The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage.4.Inductor Selection (L1)A.According to the required working conditions, select the correct inductor value using the selection guide from Figures 17 to 21.B.From the appropriate inductor selection guide, identify the inductance region intersected by the Maximum Input Voltage line and the Maximum Load Current line. Each region is identified by an inductance value and an inductor code.C.Select an appropriate inductor from the several different manufacturers part numbers listed in Table 1 or Table 2. When using Table 2 for selecting the right inductor the designer must realize that the inductor current rating must be higher than the maximum peak current flowing through the inductor. This maximum peak current can be calculated as follows:ǒVinVoutǓton+I)Ip(max)Load(max)2Lwhere ton is the “on” time of the power switch andVton+outx1foscVinFor additional information about the inductor, see the inductor section in the “External Components” section of this data sheet.Given Parameters:Vout = 5.0 VVin(max) = 20 VILoad(max) = 0.8 A1.Controller IC SelectionAccording to the required input voltage, output voltage,current polarity and current value, use the LM2575−5controller IC2.Input Capacitor Selection (Cin)A47 mF, 25 V aluminium electrolytic capacitor located nearto the input and ground pins provides sufficient bypassing.Example3.Catch Diode Selection (D1)A.For this example the current rating of the diode is 1.0 A.B.Use a 30 V 1N5818 Schottky diode, or any of thesuggested fast recovery diodes shown in the Table 4.4.Inductor Selection (L1)A.Use the inductor selection guide shown in Figures 17to 21.B.From the selection guide, the inductance area intersected by the 20 V line and 0.8 A line is L330.C.Inductor value required is 330 mH. From the Table 1 or Table 2, choose an inductor from any of the listed manufacturers.http://onsemi.com

LM2575

Procedure (Fixed Output Voltage Version) (continued)In order to simplify the switching regulator design, a step−by−step design

procedure and example is provided.

Procedure

5.Output Capacitor Selection (Cout)

A.Since the LM2575 is a forward−mode switching regulator with voltage mode control, its open loop 2−pole−2−zero frequency characteristic has the dominant pole−pair

determined by the output capacitor and inductor values. For stable operation and an acceptable ripple voltage,

(approximately 1% of the output voltage) a value between 100 mF and 470 mF is recommended.

B.Due to the fact that the higher voltage electrolytic capacitors generally have lower ESR (Equivalent Series Resistance) numbers, the output capacitor’s voltage rating should be at least 1.5 times greater than the output voltage. For a 5.0 V regulator, a rating at least 8V is appropriate, and a 10 V or 16 V rating is recommended.

Example

5.Output Capacitor Selection (Cout)

A.Cout = 100 mF to 470 mF standard aluminium electrolytic.

B.Capacitor voltage rating = 16 V.

Procedure (Adjustable Output Version: LM2575−Adj)

ProcedureGiven Parameters:Vout = Regulated Output VoltageVin(max) = Maximum DC Input VoltageILoad(max) = Maximum Load Current1.Programming Output VoltageTo select the right programming resistor R1 and R2 value (seeFigure 14) use the following formula:Vout+VrefGiven Parameters:Vout = 8.0 VVin(max) = 12 VILoad(max) = 1.0 A1.Programming Output Voltage (selecting R1 and R2)Select R1 and R2:Vout+1.231)R2+R1Exampleǒ1)R2ǓR1where Vref = 1.23 VǒResistor R1 can be between 1.0 k and 5.0 kW. (For best temperature coefficient and stability with time, use 1% metal film resistors).VoutR2+R11VrefǒR2R1Select R1 = 1.8 kWǓVoutVref*1Ǔ+1.8kǒ8.0V*11.23VǓǒǓR2 = 9.91 kW, choose a 9.88 k metal film resistor.2.Input Capacitor Selection (Cin)To prevent large voltage transients from appearing at the input and for stable operation of the converter, an aluminium or tantalum electrolytic bypass capacitor is needed between the input pin +Vin and ground pin GND This capacitor should be located close to the IC using short leads. This capacitor should have a low ESR (Equivalent Series Resistance) value.For additional information see input capacitor section in the “External Components” section of this data sheet.3.Catch Diode Selection (D1)A.Since the diode maximum peak current exceeds the regulator maximum load current the catch diode current rating must be at least 1.2 times greater than the maximum load current. For a robust design, the diode should have a current rating equal to the maximum current limit of the LM2575 to be able to withstand a continuous output short.B.The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage.2.Input Capacitor Selection (Cin)A 100 mF aluminium electrolytic capacitor located near the input and ground pin provides sufficient bypassing.3.Catch Diode Selection (D1)A.For this example, a 3.0 A current rating is adequate.B.Use a 20 V 1N5820 or MBR320 Schottky diode or any suggested fast recovery diode in the Table 4.http://onsemi.com

LM2575

Procedure (Adjustable Output Version: LM2575−Adj) (continued)

Procedure4.Inductor Selection (L1)A.Use the following formula to calculate the inductor Volt x microsecond [V x ms] constant:Vout6x10[Vxms]ExT+VVoutinF[Hz]VonExample4.Inductor Selection (L1)A.Calculate E x T [V x ms] constant:ExT+ǒ128.0Ǔx8.0x1000+51[Vxms]1252B.E x T = 51 [V x ms]ǒǓB.Match the calculated E x T value with the corresponding number on the vertical axis of the Inductor Value Selection Guide shown in Figure 21. This E x T constant is a measure of the energy handling capability of an inductor and is dependent upon the type of core, the core area, the number of turns, and the duty cycle.C.Next step is to identify the inductance region intersected by the E x T value and the maximum load current value on the horizontal axis shown in Figure 21.D.From the inductor code, identify the inductor value. Then select an appropriate inductor from the Table 1 or Table 2. The inductor chosen must be rated for a switching frequency of 52 kHz and for a current rating of 1.15 x IIoad. The inductor current rating can also be determined by calculating the inductor peak current:VVouttonin+I)Ip(max)Load(max)2LC.ILoad(max) = 1.0 AInductance Region = L220D.Proper inductor value = 220 mHChoose the inductor from the Table 1 or Table 2.ǒǓwhere ton is the “on” time of the power switch andinFor additional information about the inductor, see the inductor section in the “External Components” section of this data sheet.5.Output Capacitor Selection (Cout)A.Since the LM2575 is a forward−mode switching regulator with voltage mode control, its open loop 2−pole−2−zero frequency characteristic has the dominant pole−pair determined by the output capacitor and inductor values.For stable operation, the capacitor must satisfy the following requirement:Vin(max)[μF]Coutw7.785VoutxL[μH]B.Capacitor values between 10 mF and 2000 mF will satisfy the loop requirements for stable operation. To achieve an acceptable output ripple voltage and transient response, the output capacitor may need to be several times larger than the above formula yields.C.Due to the fact that the higher voltage electrolytic capacitorsgenerally have lower ESR (Equivalent Series Resistance) numbers, the output capacitor’s voltage rating should be at least 1.5 times greater than the output voltage. For a 5.0 V regulator, a rating of at least 8V is appropriate, and a 10 V or 16 V rating is recommended.5.Output Capacitor Selection (Cout)A.Coutw7.78512+53μF8.220To achieve an acceptable ripple voltage, selectCout = 100 mF electrolytic capacitor.ton+VoutVx1foschttp://onsemi.com

LM2575

INDUCTOR VALUE SELECTION GUIDE

60Vin, MAXIMUM INPUT VOLTAGE (V)2015108.07.06.0H1000L680L470L330L220L150L1005.00.2604025201512109.08.0

L1507.00.20.30.40.50.60.70.80.91.0H1500H1000L680L470L330L2200.30.40.50.60.81.0Vin, MAXIMUM INPUT VOLTAGE (V)IL, MAXIMUM LOAD CURRENT (A)IL, MAXIMUM LOAD CURRENT (A)

Figure 17. LM2575−3.3Figure 18. LM2575−5.0

60Vin, MAXIMUM INPUT VOLTAGE (V)Vin, MAXIMUM INPUT VOLTAGE (V)4030252018171615140.2

L680L470L330L2200.3

0.4

0.5

0.6

0.70.80.91.0

H2200H1500H1000H680H470604035302522201918170.2L680H2200H1500H1000H680H470L470L330L2200.30.40.50.60.70.80.91.0IL, MAXIMUM LOAD CURRENT (A)IL, MAXIMUM LOAD CURRENT (A)

Figure 19. LM2575−12Figure 20. LM2575−15

200150125100807060504030200.2

H2200H1500H1000H680H470ET, VOLTAGE TIME (Vμ s)L680L470L330L220L150L1000.3

0.4

0.5

0.6

0.70.80.91.0

IL, MAXIMUM LOAD CURRENT (A)

Figure 21. LM2575−Adj

NOTE: This Inductor Value Selection Guide is applicable for continuous mode only.

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LM2575

Table 1. Inductor Selection Guide

InductorCodeL100L150L220L330L470L680H150H220H330H470H680H1000H1500H2200

InductorValue100 mH150 mH220 mH330 mH470 mH680 mH150 mH220 mH330 mH470 mH680 mH1000 mH1500 mH2200 mH

Pulse EngPE−92108PE−53113PE−52626PE−52627PE−53114PE−52629PE−53115PE−53116PE−53117PE−53118PE−53119PE−53120PE−53121PE−53122

RencoRL2444RL1954RL1953RL1952RL1951RL1950RL2445RL2446RL2447RL1961RL1960RL1959RL1958RL2448

AIE415−0930415−0953415−0922415−09215−0927415−0928415−09330−06330−0635430−0634415−0935415−0934415−0933415−0945

Tech 3977 308 BV77 358 BV77 408 BV77 458 BV

−77 508 BV77 368 BV77 410 BV77 460 BV

−77 510 BV77 558 BV

−77 610 BV

Table 2. Inductor Selection Guide

Inductance

(mH)

Current(A)0.32

0.580.991.780.48

100

0.821.470.39

150

0.661.200.32

220

0.551.00

330

0.420.80

THT67143940671439906714407067144140671439806714406067144130

−67144050671441206714396067144040671441106714403067144100

Schott

SMT671443106714436067144450671445206714435067144440671445106714434067144430671445006714433067144420671444906714441067144480

THTRL−1284−68−43RL−5470−6RL−5471−5RL−5471−5RL−5470−5RL−5471−4RL−5471−4RL−5470−4RL−5471−3RL−5471−3RL−5470−3RL−5471−2RL−5471−2RL−5471−1RL−5471−1

Renco

SMTRL1500−68RL1500−68RL1500−68

−RL1500−100RL1500−100

−RL1500−150RL1500−150

−RL1500−220RL1500−220

−RL1500−330

−

Pulse EngineeringTHTPE−53804PE−53812PE−53821PE−53830PE−53811PE−53820PE−53829PE−53810PE−53819PE−53828PE−53809PE−53818PE−53827PE−53817PE−53826

SMTPE−53804−SPE−53812−SPE−53821−SPE−53830−SPE−53811−SPE−53820−SPE−53829−SPE−53810−SPE−53819−SPE−53828−SPE−53809−SPE−53818−SPE−53827−SPE−53817−SPE−53826−S

CoilcraftSMTDO1608−68DO3308−683DO3316−683DO5022P−683DO3308−104DO3316−104DO5022P−104DO3308−154DO3316−154DO5022P−154DO3308−224DO3316−224DO5022P−224DO3316−334DO5022P−334

NOTE: Table 1 and Table 2 of this Indicator Selection Guide shows some examples of different manufacturer products suitable for designwith the LM2575.

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LM2575

Table 3. Example of Several Inductor Manufacturers Phone/Fax Numbers

Pulse Engineering Inc.Pulse Engineering Inc. EuropeRenco Electronics Inc.AIE MagneticsCoilcraft Inc.Coilcraft Inc., EuropeTech 39Schott Corp.

PhoneFaxPhoneFaxPhoneFaxPhoneFaxPhoneFaxPhoneFaxPhoneFaxPhoneFax

+ 1−619−674−8100+ 1−619−674−8262+ 353 93 24 107+ 353 93 24 459+ 1−516−5−5828+ 1−516−586−5562+ 1−813−347−2181+ 1−708−322−25+ 1−708−639−1469+ 44 1236 730 595+ 44 1236 730 627+ 33 8425 2626+ 33 8425 2610+ 1−612−475−1173+ 1−612−475−1786

Table 4. Diode Selection Guide gives an overview about both surface−mount and through−hole diodes for an

effective design. Device listed in bold are available from ON Semiconductor.

Schottky

1.0 A

VR20 V

SMTSK12

THT1N5817SR1021N5818SR10311DQ031N5819SR10411DQ04MBR150SR10511DQ05

SMTSK32MBRD320SK33MBRD330

3.0 A

THT1N5820MBR320SR3021N5821MBR330SR30331DQ031N5822MBR340SR30431DQ04MBR350SR30511DQ05

MURS120T3

MURS320T3

MUR12011DF1HER102

MURD320

MUR32030WF10MUR420

SMT

1.0 A

THT

SMT

Ultra−Fast Recovery

3.0 A

THT

30 V

MBRS130LT3

SK13

40 V

MBRS140T3

SK1410BQ04010MQ040MBRS15010BQ050

MBRS340T3MBRD34030WQ04SK34MBRD350SK3530WQ05

10BF10

50 V

31DF1HER302

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LM2575

EXTERNAL COMPONENTS

Input Capacitor (Cin)

The Input Capacitor Should Have a Low ESR

For stable operation of the switch mode converter a lowESR (Equivalent Series Resistance) aluminium or solidtantalum bypass capacitor is needed between the input pinand the ground pin to prevent large voltage transients fromappearing at the input. It must be located near the regulatorand use short leads. With most electrolytic capacitors, thecapacitance value decreases and the ESR increases withlower temperatures. For reliable operation in temperaturesbelow −25°C larger values of the input capacitor may beneeded. Also paralleling a ceramic or solid tantalumcapacitor will increase the regulator stability at coldtemperatures.

RMS Current Rating of Cin

(below 0.05 W), there is a possibility of an unstable feedbackloop, resulting in oscillation at the output. This situation canoccur when a tantalum capacitor, that can have a very lowESR, is used as the only output capacitor.

At Low Temperatures, Put in Parallel AluminiumElectrolytic Capacitors with Tantalum Capacitors

The important parameter of the input capacitor is the RMScurrent rating. Capacitors that are physically large and havelarge surface area will typically have higher RMS currentratings. For a given capacitor value, a higher voltageelectrolytic capacitor will be physically larger than a lowervoltage capacitor, and thus be able to dissipate more heat tothe surrounding air, and therefore will have a higher RMScurrent rating. The consequence of operating an electrolyticcapacitor above the RMS current rating is a shortenedoperating life. In order to assure maximum capacitoroperating lifetime, the capacitor’s RMS ripple current ratingshould be:

Irms > 1.2 x d x ILoad

Electrolytic capacitors are not recommended fortemperatures below −25°C. The ESR rises dramatically atcold temperatures and typically rises 3 times at −25°C andas much as 10 times at −40°C. Solid tantalum capacitorshave much better ESR spec at cold temperatures and arerecommended for temperatures below −25°C. They can bealso used in parallel with aluminium electrolytics. The valueof the tantalum capacitor should be about 10% or 20% of thetotal capacitance. The output capacitor should have at least50% higher RMS ripple current rating at 52 kHz than thepeak−to−peak inductor ripple current.

Catch Diode

Locate the Catch Diode Close to the LM2575

The LM2575 is a step−down buck converter; it requires afast diode to provide a return path for the inductor currentwhen the switch turns off. This diode must be located closeto the LM2575 using short leads and short printed circuittraces to avoid EMI problems.

Use a Schottky or a Soft SwitchingUltra−Fast Recovery Diode

where d is the duty cycle, for a buck regulator

d+on+out

TVin

|Vout|t

andd+on+forabuck*boostregulator.

T|Vout|)Vin

For low output ripple voltage and good stability, low ESRoutput capacitors are recommended. An output capacitorhas two main functions: it filters the output and providesregulator loop stability. The ESR of the output capacitor andthe peak−to−peak value of the inductor ripple current are themain factors contributing to the output ripple voltage value.Standard aluminium electrolytics could be adequate forsome applications but for quality design low ESR types arerecommended.

An aluminium electrolytic capacitor’s ESR value isrelated to many factors such as the capacitance value, thevoltage rating, the physical size and the type of construction.In most cases, the higher voltage electrolytic capacitors havelower ESR value. Often capacitors with much highervoltage ratings may be needed to provide low ESR valuesthat are required for low output ripple voltage.

The Output Capacitor Requires an ESR ValueThat Has an Upper and Lower Limit

Output Capacitor (Cout)

Since the rectifier diodes are very significant source oflosses within switching power supplies, choosing therectifier that best fits into the converter design is animportant process. Schottky diodes provide the bestperformance because of their fast switching speed and lowforward voltage drop.

They provide the best efficiency especially in low outputvoltage applications (5.0 V and lower). Another choicecould be Fast−Recovery, or Ultra−Fast Recovery diodes. Ithas to be noted, that some types of these diodes with anabrupt turnoff characteristic may cause instability or EMItroubles.

A fast−recovery diode with soft recovery characteristicscan better fulfill a quality, low noise design requirements.Table 4 provides a list of suitable diodes for the LM2575regulator. Standard 50/60 Hz rectifier diodes such as the1N4001 series or 1N5400 series are NOT suitable.

Inductor

As mentioned above, a low ESR value is needed for lowoutput ripple voltage, typically 1% to 2% of the outputvoltage. But if the selected capacitor’s ESR is extremely low

The magnetic components are the cornerstone of allswitching power supply designs. The style of the core andthe winding technique used in the magnetic component’sdesign has a great influence on the reliability of the overallpower supply.

Using an improper or poorly designed inductor can causehigh voltage spikes generated by the rate of transitions incurrent within the switching power supply, and thepossibility of core saturation can arise during an abnormaloperational mode. Voltage spikes can cause thesemiconductors to enter avalanche breakdown and the partcan instantly fail if enough energy is applied. It can also

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LM2575

cause significant RFI (Radio Frequency Interference) andEMI (Electro−Magnetic Interference) problems.

Continuous and Discontinuous Mode of Operation

The LM2575 step−down converter can operate in both thecontinuous and the discontinuous modes of operation. Theregulator works in the continuous mode when loads arerelatively heavy, the current flows through the inductorcontinuously and never falls to zero. Under light loadconditions, the circuit will be forced to the discontinuousmode when inductor current falls to zero for certain periodof time (see Figure 22 and Figure 23). Each mode hasdistinctively different operating characteristics, which canaffect the regulator performance and requirements. In manycases the preferred mode of operation is the continuousmode. It offers greater output power, lower peak currents inthe switch, inductor and diode, and can have a lower outputripple voltage. On the other hand it does require largerinductor values to keep the inductor current flowingcontinuously, especially at low output load currents and/orhigh input voltages.

To simplify the inductor selection process, an inductorselection guide for the LM2575 regulator was added to thisdata sheet (Figures 17 through 21). This guide assumes thatthe regulator is operating in the continuous mode, andselects an inductor that will allow a peak−to−peak inductorripple current to be a certain percentage of the maximumdesign load current. This percentage is allowed to change asdifferent design load currents are selected. For light loads(less than approximately 200 mA) it may be desirable tooperate the regulator in the discontinuous mode, because theinductor value and size can be kept relatively low.Consequently, the percentage of inductor peak−to−peakcurrent increases. This discontinuous mode of operation isperfectly acceptable for this type of switching converter.Any buck regulator will be forced to enter discontinuousmode if the load current is light enough.

POWER SWITCHCURRENT (A)the physical volume the inductor must fit within, and theamount of EMI (Electro−Magnetic Interference) shieldingthat the core must provide. The inductor selection guidecovers different styles of inductors, such as pot core, E−core,toroid and bobbin core, as well as different core materialssuch as ferrites and powdered iron from differentmanufacturers.

For high quality design regulators the toroid core seems tobe the best choice. Since the magnetic flux is completelycontained within the core, it generates less EMI, reducingnoise problems in sensitive circuits. The least expensive isthe bobbin core type, which consists of wire wound on aferrite rod core. This type of inductor generates more EMIdue to the fact that its core is open, and the magnetic flux isnot completely contained within the core.

When multiple switching regulators are located on thesame printed circuit board, open core magnetics can causeinterference between two or more of the regulator circuits,especially at high currents due to mutual coupling. A toroid,pot core or E−core (closed magnetic structure) should beused in such applications.

Do Not Operate an Inductor Beyond itsMaximum Rated Current

1.0

Exceeding an inductor’s maximum current rating maycause the inductor to overheat because of the copper wirelosses, or the core may saturate. Core saturation occurs whenthe flux density is too high and consequently the crosssectional area of the core can no longer support additionallines of magnetic flux.

This causes the permeability of the core to drop, theinductance value decreases rapidly and the inductor beginsto look mainly resistive. It has only the dc resistance of thewinding. This can cause the switch current to rise veryrapidly and force the LM2575 internal switch intocycle−by−cycle current limit, thus reducing the dc outputload current. This can also result in overheating of theinductor and/or the LM2575. Different inductor types havedifferent saturation characteristics, and this should be keptin mind when selecting an inductor.

POWER SWITCHCURRENT (A)INDUCTORCURRENT (A)0

0.1 0

INDUCTORCURRENT (A)1.0

0.1 0

HORIZONTAL TIME BASE: 5.0 ms/DIV

Figure 22. Continuous Mode Switching

Current Waveforms

Selecting the Right Inductor Style

Some important considerations when selecting a core typeare core material, cost, the output power of the power supply,

Figure 23. Discontinuous Mode Switching

Current Waveforms

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LM2575

GENERAL RECOMMENDATIONS

Output Voltage Ripple and TransientsSource of the Output Ripple

Heatsinking and Thermal ConsiderationsThe Through−Hole Package TO−220

Since the LM2575 is a switch mode power supplyregulator, its output voltage, if left unfiltered, will contain asawtooth ripple voltage at the switching frequency. Theoutput ripple voltage value ranges from 0.5% to 3% of theoutput voltage. It is caused mainly by the inductor sawtoothripple current multiplied by the ESR of the output capacitor.

Short Voltage Spikes and How to Reduce Them

The regulator output voltage may also contain shortvoltage spikes at the peaks of the sawtooth waveform (seeFigure 24). These voltage spikes are present because of thefast switching action of the output switch, and the parasiticinductance of the output filter capacitor. There are someother important factors such as wiring inductance, straycapacitance, as well as the scope probe used to evaluate thesetransients, all these contribute to the amplitude of thesespikes. To minimize these voltage spikes, low inductancecapacitors should be used, and their lead lengths must bekept short. The importance of quality printed circuit boardlayout design should also be highlighted.

Voltage spikes caused by switching action of the outputswitch and the parasitic inductance of the output capacitorThe LM2575 is available in two packages, a 5−pinTO−220(T, TV) and a 5−pin surface mount D2PAK(D2T).There are many applications that require no heatsink to keepthe LM2575 junction temperature within the allowedoperating range. The TO−220 package can be used withouta heatsink for ambient temperatures up to approximately50°C (depending on the output voltage and load current).Higher ambient temperatures require some heatsinking,either to the printed circuit (PC) board or an externalheatsink.

The Surface Mount Package D2PAK and itsHeatsinking

UNFILTEREDOUTPUTVOLTAGEVERTICALRESOLUTION:20 mV/DIVFILTEREDOUTPUTVOLTAGE

The other type of package, the surface mount D2PAK, isdesigned to be soldered to the copper on the PC board. Thecopper and the board are the heatsink for this package andthe other heat producing components, such as the catchdiode and inductor. The PC board copper area that thepackage is soldered to should be at least 0.4 in2 (or 100 mm2)and ideally should have 2 or more square inches (1300 mm2)of 0.0028 inch copper. Additional increasing of copper areabeyond approximately 3.0 in2 (2000 mm2) will not improveheat dissipation significantly. If further thermalimprovements are needed, double sided or multilayer PCboards with large copper areas should be considered.

Thermal Analysis and Design

HORIZONTAL TIME BASE: 10 ms/DIV

Figure 24. Output Ripple Voltage WaveformsMinimizing the Output Ripple

In order to minimize the output ripple voltage it is possibleto enlarge the inductance value of the inductor L1 and/or touse a larger value output capacitor. There is also another wayto smooth the output by means of an additional LC filter(20 mH, 100 mF), that can be added to the output (seeFigure 33) to further reduce the amount of output ripple andtransients. With such a filter it is possible to reduce theoutput ripple voltage transients 10 times or more. Figure 24shows the difference between filtered and unfiltered outputwaveforms of the regulator shown in Figure 33.

The upper waveform is from the normal unfiltered outputof the converter, while the lower waveform shows the outputripple voltage filtered by an additional LC filter.

The following procedure must be performed to determinewhether or not a heatsink will be required. First determine:1.PD(max) maximum regulator power dissipation in

the application.

2.TA(max) maximum ambient temperature in the

application.

3.TJ(max)maximum allowed junction temperature

(125°C for the LM2575). For a conservativedesign, the maximum junction temperature should not exceed 110°C to assure safe operation. For every additional 10°C temperature rise that the junction must withstand, the estimated operating lifetimeof the component is halved.

4.RqJCpackage thermal resistance junction−case.

package thermal resistance junction−ambient.5.RqJA

(Refer to Absolute Maximum Ratings in this data sheet orRqJC and RqJA values).

The following formula is to calculate the total powerdissipated by the LM2575:

PD = (Vin x IQ) + d x ILoad x Vsat

where d is the duty cycle and for buck converter

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LM2575

d+on+O,

VinTUnregulatedDC Input12 V to 25 VCin100 mF/50 VFeedback +Vin13LM2575−12GND54Output2ON/OFFL1100 mHD11N5819Cout1800 mF/16 VRegulatedOutput-12 V @ 0.35 A

IQVinVOILoad

(quiescent current) and Vsat can be found in theLM2575 data sheet,

is minimum input voltage applied,is the regulator output voltage,is the load current.

The dynamic switching losses during turn−on andturn−off can be neglected if proper type catch diode is used.

Packages Not on a Heatsink (Free−Standing)

For a free−standing application when no heatsink is used,the junction temperature can be determined by the followingexpression:

TJ = (RqJA) (PD) + TA

Figure 25. Inverting Buck−Boost Regulator Using the

LM2575−12 Develops −12 V @ 0.35 A

ADDITIONAL APPLICATIONS

Inverting Regulator

where (RqJA)(PD) represents the junction temperature risecaused by the dissipated power and TA is the maximumambient temperature.

Packages on a Heatsink

If the actual operating junction temperature is greater thanthe selected safe operating junction temperature determinedin step 3, than a heatsink is required. The junctiontemperature will be calculated as follows:

TJ = PD (RqJA + RqCS + RqSA) + TA

where

RqJC is the thermal resistance junction−case,RqCS is the thermal resistance case−heatsink,RqSA is the thermal resistance heatsink−ambient.

If the actual operating temperature is greater than theselected safe operating junction temperature, then a largerheatsink is required.

Some Aspects That can Influence Thermal Design

It should be noted that the package thermal resistance andthe junction temperature rise numbers are all approximate,and there are many factors that will affect these numbers,such as PC board size, shape, thickness, physical position,location, board temperature, as well as whether thesurrounding air is moving or still.

Other factors are trace width, total printed circuit copperarea, copper thickness, single− or double−sided, multilayerboard, the amount of solder on the board or even color of thetraces.

The size, quantity and spacing of other components onthe board can also influence its effectiveness to dissipatethe heat.

An inverting buck−boost regulator using the LM2575−12is shown in Figure 25. This circuit converts a positive inputvoltage to a negative output voltage with a common groundby bootstrapping the regulators ground to the negativeoutput voltage. By grounding the feedback pin, the regulatorsenses the inverted output voltage and regulates it.

In this example the LM2575−12 is used to generate a−12 V output. The maximum input voltage in this casecannot exceed +28 V because the maximum voltageappearing across the regulator is the absolute sum of theinput and output voltages and this must be limited to amaximum of 40 V.

This circuit configuration is able to deliver approximately0.35 A to the output when the input voltage is 12 V or higher.At lighter loads the minimum input voltage required dropsto approximately 4.7 V, because the buck−boost regulatortopology can produce an output voltage that, in its absolutevalue, is either greater or less than the input voltage.

Since the switch currents in this buck−boost configurationare higher than in the standard buck converter topology, theavailable output current is lower.

This type of buck−boost inverting regulator can alsorequire a larger amount of startup input current, even forlight loads. This may overload an input power source witha current limit less than 1.5 A.

Such an amount of input startup current is needed for atleast 2.0 ms or more. The actual time depends on the outputvoltage and size of the output capacitor.

Because of the relatively high startup currents required bythis inverting regulator topology, the use of a delayed startupor an undervoltage lockout circuit is recommended.

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LM2575

Using a delayed startup arrangement, the input capacitorcan charge up to a higher voltage before the switch−moderegulator begins to operate.

The high input current needed for startup is now partiallysupplied by the input capacitor Cin.

Design Recommendations:

+Vin +Vin1CinR147 k100 mF5LM2575−XXThe inverting regulator operates in a different manner

than the buck converter and so a different design procedurehas to be used to select the inductor L1 or the outputcapacitor Cout.

The output capacitor values must be larger than isnormally required for buck converter designs. Low inputvoltages or high output currents require a large value outputcapacitor (in the range of thousands of mF).

The recommended range of inductor values for theinverting converter design is between 68 mH and 220 mH. Toselect an inductor with an appropriate current rating, theinductor peak current has to be calculated.

The following formula is used to obtain the peak inductorcurrent:

I(V)|V|)

O)Vinxton[Loadin

peakV2L1

|V|Owhereton+x1,andfosc+52kHz.V)|V|foscinO

5.0 V0OnShutdownInputOffR3470ON/OFF3GNDR247 k-VoutMOC8101NOTE: This picture does not show the complete circuit.

Figure 27. Inverting Buck−Boost Regulator Shut Down

Circuit Using an Optocoupler

With the inverting configuration, the use of the ON/OFFpin requires some level shifting techniques. This is causedby the fact, that the ground pin of the converter IC is nolonger at ground. Now, the ON/OFF pin threshold voltage(1.4 V approximately) has to be related to the negativeoutput voltage level. There are many different possible shutdown methods, two of them are shown in Figures 27 and 28.

+V0OnR25.6 k +VinCin100 mFQ12N39065 +Vin1LM2575−XXOffShutdownInputUnder normal continuous inductor current operatingconditions, the worst case occurs when Vin is minimal.Note that the voltage appearing across the regulator is theabsolute sum of the input and output voltage, and must notexceed 40 V.

UnregulatedDC Input12 V to 25 VCinC1100 mF0.1 mF/50 VFeedback +Vin1LM2575−125R147 kON/OFF3L14100 mHOutput2GNDD11N5819Cout1800 mF/16 VON/OFF3R112 kGNDR247 k-VoutNOTE: This picture does not show the complete circuit.

RegulatedOutput-12 V @ 0.35 A

Figure 28. Inverting Buck−Boost Regulator Shut Down

Circuit Using a PNP TransistorNegative Boost Regulator

Figure 26. Inverting Buck−BoostRegulator with Delayed Startup

It has been already mentioned above, that in somesituations, the delayed startup or the undervoltage lockoutfeatures could be very useful. A delayed startup circuitapplied to a buck−boost converter is shown in Figure 26.Figure 32 in the “Undervoltage Lockout” section describesan undervoltage lockout feature for the same convertertopology.

This example is a variation of the buck−boost topologyand is called a negative boost regulator. This regulatorexperiences relatively high switch current, especially at lowinput voltages. The internal switch current limiting results inlower output load current capability.

The circuit in Figure 29 shows the negative boostconfiguration. The input voltage in this application rangesfrom −5.0 V to −12 V and provides a regulated −12 V output.

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LM2575

If the input voltage is greater than −12 V, the output will riseabove −12 V accordingly, but will not damage the regulator.

cause some problems by coupling the ripple into theON/OFF pin, the regulator could be switched periodicallyon and off with the line (or double) frequency.

4 +Vin1Cin100 mF/50 V3GND5LM2575−12FeedbackOutput2ON/OFFD1Cout1000 mF/16 V +Vin +Vin1C10.1 mF5LM2575−XX1N5817RegulatedOutputVout = -12 VLoad Current from200 mA for Vin = -5.2 Vto 500 mA for Vin = -7.0 VON/OFF3GNDCin100 mFR147 kL1UnregulatedDC Input

-Vin = -5.0 V to -12 V

150 mHR247 kNOTE: This picture does not show the complete circuit.

Figure 29. Negative Boost Regulator

Design Recommendations:

Figure 30. Delayed Startup Circuitry

Undervoltage Lockout

The same design rules as for the previous invertingbuck−boost converter can be applied. The output capacitorCout must be chosen larger than would be required for astandard buck converter. Low input voltages or high outputcurrents require a large value output capacitor (in the rangeof thousands of mF). The recommended range of inductorvalues for the negative boost regulator is the same as forinverting converter design.

Another important point is that these negative boostconverters cannot provide current limiting load protection inthe event of a short in the output so some other means, suchas a fuse, may be necessary to provide the load protection.

Delayed Startup

Some applications require the regulator to remain off untilthe input voltage reaches a certain threshold level. Figure 31shows an undervoltage lockout circuit applied to a buckregulator. A version of this circuit for buck−boost converteris shown in Figure 32. Resistor R3 pulls the ON/OFF pinhigh and keeps the regulator off until the input voltagereaches a predetermined threshold level, which isdetermined by the following expression:

Vth[V

(Q1))1)R2V

R1BE

ǒǓ +Vin +Vin1LM2575−5.0There are some applications, like the inverting regulatoralready mentioned above, which require a higher amount ofstartup current. In such cases, if the input power source islimited, this delayed startup feature becomes very useful.To provide a time delay between the time the input voltageis applied and the time when the output voltage comes up,the circuit in Figure 30 can be used. As the input voltage isapplied, the capacitor C1 charges up, and the voltage acrossthe resistor R2 falls down. When the voltage on the ON/OFFpin falls below the threshold value 1.4 V, the regulator startsup. Resistor R1 is included to limit the maximum voltageapplied to the ON/OFF pin, reduces the power supply noisesensitivity, and also limits the capacitor C1 dischargecurrent, but its use is not mandatory.

When a high 50 Hz or 60 Hz (100 Hz or 120 Hzrespectively) ripple voltage exists, a long delay time can

R210 kR347 kCin100 mF5ON/OFF3GNDZ11N5242BQ12N3904R110 kVth ≈ 13 VNOTE: This picture does not show the complete circuit.

Figure 31. Undervoltage Lockout Circuit for

Buck Converter

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LM2575

Adjustable Output, Low−Ripple Power Supply

+Vin +Vin1R215 kR368 kCin100 mF5LM2575−5.0ON/OFF3GNDA 1.0 A output current capability power supply thatfeatures an adjustable output voltage is shown in Figure 33.This regulator delivers 1.0 A into 1.2 V to 35 V output.The input voltage ranges from roughly 8.0 V to 40 V. In orderto achieve a 10 or more times reduction of output ripple, anadditional L−C filter is included in this circuit.

Z11N5242BQ12N3904R115 kVth ≈ 13 VVout = -5.0 VNOTE: This picture does not show the complete circuit.

Figure 32. Undervoltage Lockout Circuit for

Buck−Boost Converter

FeedbackUnregulatedDC Input+

+Vin13Cin100 mF/50 V4LM2575−AdjOutputGND52ON/OFFL1150 mHR250 kD11N5819Cout2200 mFC1100 mFR11.1 kL220 mHRegulatedOutput Voltage1.2 V to 35 V @1.0 AOptional OutputRipple Filter

Figure 33. Adjustable Power Supply with Low Ripple Voltage

RθJA, THERMAL RESISTANCEPD(max) for TA = 50°CJUNCTION‐TO‐AIR ( ° C/W)70605040RqJA3005.010152025301.0

Free AirMountedVertically3.0

2.0 oz. CopperLMinimumSize PadL2.52.01.5

L, LENGTH OF COPPER (mm)

Figure 34. D2PAK Thermal Resistance and MaximumPower Dissipation versus P.C.B. Copper Length

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PD, MAXIMUM POWER DISSIPATION (W)803.5

LM2575

THE LM2575−5.0 STEP−DOWN VOLTAGE REGULATOR WITH 5.0 V @ 1.0 A OUTPUT POWER

CAPABILITY. TYPICAL APPLICATION WITH THROUGH−HOLE PC BOARD LAYOUT

FeedbackUnregulated DC Input

+Vin = +7.0 V to +40 V

+Vin13C1100 mF/50 V4LM2575−5.0OutputGND52ON/OFFL1330 mHRegulated Output+Vout1 = 5.0 V @ 1.0 A

J1D11N5819Cout330 mF/16 VGNDout

GNDinC1C2D1L1−−−−100 mF, 50 V, Aluminium Electrolytic330 mF, 16 V, Aluminium Electrolytic1.0 A, 40 V, Schottky Rectifier, 1N5819

330 mH, Tech 39: 77 458 BV, Toroid Core, Through−Hole, Pin 3 = Start, Pin 7 = Finish

Figure 35. Schematic Diagram of the LM2575−5.0 Step−Down Converter

GNDinC1U1 LM2575GNDoutL1D1J1C2DC-DC Converter+VinNOTE: Not to scale.

+Vout1NOTE: Not to scale.

Figure 36. Printed Circuit Board

Component SideFigure 37. Printed Circuit Board

Copper Side

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LM2575

THE LM2575−ADJ STEP−DOWN VOLTAGE REGULATOR WITH 8.0 V @ 1.0 A OUTPUT POWER

CAPABILITY. TYPICAL APPLICATION WITH THROUGH−HOLE PC BOARD LAYOUT

Regulated

Output UnfilteredVout1 = 8.0 V @1.0 A4UnregulatedDC Input+Vin = +10 V to + 40 V +Vin13C1100 mF/50 VFeedbackLM2575−AdjOutputGND52ON/OFFL1330 mHL225 mHRegulatedOutput FilteredVout2 = 8.0 V @1.0 AR210 kD11N5819C2330 mF/16 VR11.8 kC3100 mF/16 VVC1C2C3D1L1L2R1R2

−−−−−−−−

R2out+Vref)1)R1ǒǓ100 mF, 50 V, Aluminium ElectrolyticR1 is between 1.0 k and 5.0 k330 mF, 16 V, Aluminium Electrolytic100 mF, 16 V, Aluminium Electrolytic1.0 A, 40 V, Schottky Rectifier, 1N5819

330 mH, Tech 39: 77 458 BV, Toroid Core, Through−Hole, Pin 3 = Start, Pin 7 = Finish25 mH, TDK: SFT52501, Toroid Core, Through−Hole1.8 k10 k

Vref = 1.23 V

Figure 38. Schematic Diagram of the 8.0 V @ 1.0 V Step−Down Converter Using the LM2575−Adj

(An additional LC filter is included to achieve low output ripple voltage)

GNDinC1L1U1 LM2575C2D1J1GNDoutC3L2+VinR2R1NOTE: Not to scale.

+Vout2+Vout1NOTE: Not to scale.

Figure 39. PC Board Component SideFigure 40. PC Board Copper Side

References

••••

National Semiconductor LM2575 Data Sheet and Application NoteNational Semiconductor LM2595 Data Sheet and Application Note

Marty Brown “Practical Switching Power Supply Design”, Academic Press, Inc., San Diego 1990Ray Ridley “High Frequency Magnetics Design”, Ridley Engineering, Inc. 1995

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LM2575

ORDERING INFORMATION

Device

LM2575TV−ADJLM2575TV−ADJGLM2575T−ADJLM2575T−ADJGLM2575D2T−ADJLM2575D2T−ADJGLM2575D2T−ADJR4LM2575D2T−ADJR4GLM2575TV−3.3LM2575TV−3.3GLM2575T−3.3LM2575T−3.3GLM2575D2T−3.3LM2575D2T−3.3GLM2575D2T−3.3R4LM2575D2T−3.3R4GLM2575TV−005LM2575TV−005GLM2575T−005LM2575T−005GLM2575D2T−005LM2575D2T−005GLM2575D2T−5R4LM2575D2T−5R4GLM2575TV−012LM2575TV−012GLM2575T−012LM2575T−012GLM2575D2T−012LM2575D2T−012GLM2575D2T−12R4LM2575D2T−12R4G

12 V

TJ = −40° to +125°C

5.0 V

TJ = −40° to +125°C

3.3 V

TJ = −40° to +125°C

1.23 V to 37 V

TJ = −40° to +125°C

NominalOutput Voltage

Operating

Temperature Range

Package

TO−220 (Vertical Mount)TO−220 (Vertical Mount)

(Pb−Free)TO−220 (Straight Lead)TO−220 (Straight Lead)

(Pb−Free)D2PAK (Surface Mount)D2PAK (Surface Mount)

(Pb−Free)TO−220 (Vertical Mount)TO−220 (Vertical Mount)

(Pb−Free)TO−220 (Straight Lead)TO−220 (Straight Lead)

(Pb−Free)D2PAK (Surface Mount)D2PAK (Surface Mount)

(Pb−Free)TO−220 (Vertical Mount)TO−220 (Vertical Mount)

(Pb−Free)TO−220 (Straight Lead)TO−220 (Straight Lead)

(Pb−Free)D2PAK (Surface Mount)D2PAK (Surface Mount)

(Pb−Free)TO−220 (Vertical Mount)TO−220 (Vertical Mount)

(Pb−Free)TO−220 (Straight Lead)TO−220 (Straight Lead)

(Pb−Free)D2PAK (Surface Mount)D2PAK (Surface Mount)

(Pb−Free)

800 Tape & Reel50 Units/Rail800 Tape & Reel50 Units/Rail800 Tape & Reel50 Units/Rail800 Tape & Reel50 Units/RailShipping†

†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel PackagingSpecifications Brochure, BRD8011/D.

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LM2575

ORDERING INFORMATION

Device

LM2575TV−015LM2575TV−015GLM2575T−015LM2575T−015GLM2575D2T−015LM2575D2T−015GLM2575D2T−15R4LM2575D2T−15R4G

15 V

TJ = −40° to +125°C

NominalOutput Voltage

Operating

Temperature Range

Package

TO−220 (Vertical Mount)TO−220 (Vertical Mount)

(Pb−Free)TO−220 (Straight Lead)TO−220 (Straight Lead)

(Pb−Free)D2PAK (Surface Mount)D2PAK (Surface Mount)

(Pb−Free)

800 Tape & Reel50 Units/RailShipping†

†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel PackagingSpecifications Brochure, BRD8011/D.

MARKING DIAGRAMS

TO−220TV SUFFIXCASE 314BTO−220T SUFFIXCASE 314DD2PAKD2T SUFFIXCASE 936A

2575T−xxxAWLYWWG

LM2575−xxxAWLYWWG

151

xxxAWLYWWG= 3.3, 5.0, 12, 15, or ADJ= Assembly Location= Wafer Lot= Year

= Work Week

= Pb−Free Package

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LM2575

PACKAGE DIMENSIONS

TO−220TV SUFFIXCASE 314B−05

ISSUE L

QB−P−COPTIONAL CHAMFEREUKFASLWVNOTES:

1.DIMENSIONING AND TOLERANCING PER ANSIY14.5M, 1982.

2.CONTROLLING DIMENSION: INCH.3.DIMENSION D DOES NOT INCLUDE

INTERCONNECT BAR (DAMBAR) PROTRUSION.DIMENSION D INCLUDING PROTRUSION SHALLNOT EXCEED 0.043 (1.092) MAXIMUM.

DIMABCDEFGHJKLNQSUVWINCHESMINMAX0.5720.6130.3900.4150.1700.1800.0250.0380.0480.0550.8500.9350.067 BSC0.166 BSC0.0150.0250.9001.1000.3200.3650.320 BSC0.1400.153---0.620

0.4680.505---0.735

0.0900.110MILLIMETERS

MINMAX14.52915.5709.90610.5414.3184.5720.6350.9651.2191.39721.59023.7491.702 BSC4.216 BSC0.3810.63522.86027.9408.12.2718.128 BSC3.5563.886---15.74811.88812.827---18.6692.2862.7945XJTHN−T−SEATINGPLANEG5XDM0.24 (0.610)M0.10 (0.254)TP

MTO−220T SUFFIXCASE 314D−04

ISSUE F

−T−−Q−BB1DETAIL A-ASEATINGPLANE

ECNOTES:

1.DIMENSIONING AND TOLERANCING PER ANSIY14.5M, 1982.

2.CONTROLLING DIMENSION: INCH.3.DIMENSION D DOES NOT INCLUDE

INTERCONNECT BAR (DAMBAR) PROTRUSION.DIMENSION D INCLUDING PROTRUSION SHALLNOT EXCEED 10.92 (0.043) MAXIMUM.

DIMABB1CDEGHJKLQUINCHESMINMAX0.5720.6130.3900.4150.3750.4150.1700.1800.0250.0380.0480.0550.067 BSC0.0870.1120.0150.0250.9771.0450.3200.3650.1400.1530.1050.117MILLIMETERS

MINMAX14.52915.5709.90610.5419.52510.5414.3184.5720.6350.9651.2191.3971.702 BSC2.2102.8450.3810.63524.81026.5438.12.2713.5563.8862.6672.972UK12345ALDG5 PLJHM0.356 (0.014)

MTQ

BB1DETAIL A−A

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LM2575

PACKAGE DIMENSIONS

D2PAKD2T SUFFIXCASE 936A−02ISSUE C

−T−AKB12345OPTIONALCHAMFERTERMINAL 6NOTES:

1.DIMENSIONING AND TOLERANCING PER ANSIY14.5M, 1982.

2.CONTROLLING DIMENSION: INCH.

3.TAB CONTOUR OPTIONAL WITHIN DIMENSIONS AAND K.

4.DIMENSIONS U AND V ESTABLISH A MINIMUMMOUNTING SURFACE FOR TERMINAL 6.

5.DIMENSIONS A AND B DO NOT INCLUDE MOLDFLASH OR GATE PROTRUSIONS. MOLD FLASHAND GATE PROTRUSIONS NOT TO EXCEED 0.025(0.635) MAXIMUM.

INCHESMINMAX0.3860.4030.3560.3680.1700.1800.0260.0360.0450.0550.067 BSC0.5390.5790.050 REF0.0000.0100.0880.1020.0180.0260.0580.078_5 REF0.116 REF0.200 MIN0.250 MINMILLIMETERSMINMAX9.80410.2369.0429.3474.3184.5720.6600.9141.1431.3971.702 BSC13.69114.7071.270 REF0.0000.2542.2352.5910.4570.6601.4731.981_5 REF2.946 REF5.080 MIN6.350 MINEVUSHMLD0.010 (0.254)MTNGRPCSOLDERING FOOTPRINT*

8.380.331.7020.06710.660.42DIMABCDEGHKLMNPRSUV16.020.633.050.121.0160.04SCALE 3:1

mmǓǒinches*For additional information on our Pb−Free strategy and soldering

details, please download the ON Semiconductor Soldering andMounting Techniques Reference Manual, SOLDERRM/D.

ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further noticeto any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liabilityarising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.“Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. Alloperating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rightsnor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applicationsintended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. ShouldBuyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates,and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or deathassociated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an EqualOpportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.

PUBLICATION ORDERING INFORMATION

LITERATURE FULFILLMENT:Literature Distribution Center for ON SemiconductorP.O. Box 5163, Denver, Colorado 80217 USAPhone: 303−675−2175 or 800−344−3860 Toll Free USA/CanadaFax: 303−675−2176 or 800−344−3867 Toll Free USA/CanadaEmail: orderlit@onsemi.comN. American Technical Support: 800−282−9855 Toll FreeUSA/CanadaEurope, Middle East and Africa Technical Support:Phone: 421 33 790 2910Japan Customer Focus CenterPhone: 81−3−5773−3850ON Semiconductor Website: www.onsemi.comOrder Literature: http://www.onsemi.com/orderlitFor additional information, please contact your localSales Representativehttp://onsemi.com28LM2575/D

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