L4960

L4960

2.5A POWER SWITCHING REGULATOR

2.5A OUTPUT CURRENT

5.1V TO 40V OPUTPUT VOLTAGE RANGEPRECISE (± 2%) ON-CHIP REFERENCEHIGH SWITCHING FREQUENCY

VERY HIGH EFFICIENCY (UP TO 90%)VERY FEW EXTERNAL COMPONENTSSOFT START

INTERNAL LIMITING CURRENTTHERMAL SHUTDOWN

HEPTAWATTORDERING NUMBERS: L4960 (Vertical) L4960H (Horizontal)DESCRIPTION

The L4960 is a monolithic power switching regula-tor delivering 2.5A at a voltage variable from 5V to40V in step down configuration.

Features of the device include current limiting, softstart, thermal protection and 0 to 100% duty cyclefor continuous operation mode.

The L4960 is mounted in a Heptawatt plastic powerpackage and requires very few external compo-nents.

Efficient operation at switching frequencies up to150KHz allows a reduction in the size and cost ofexternal filter components.

BLOCK DIAGRAM

June 20001/16

PIN CONNECTION (Top view)

ABSOLUTE MAXIMUM RATINGS

SymbolV1V1 - V7V7 V3, V6V2I3I5PtotTj, TstgParameterInput voltageInput to output voltage differenceNegative output DC voltageNegative output peak voltage at t = 0.1µs; f = 100KHzVoltage at pin 3 and 6Voltage at pin 2Pin 3 sink currentPin 5 source currentPower dissipation at Tcase ≤ 90°CJunction and storage temperatureValue5050-1-55.5712015-40 to 150UnitVVVVVVmAmAW°CPIN FUNCTIONS

N°1NAMESUPPLY VOLTAGEFUNCTIONUnregulated voltage input. An internal regulator powers theinternal logic.The feedback terminal of the regulation loop. The output isconnected directly to this terminal for 5.1V operation; it isconnected via a divider for higher voltages.A series RC network connected between this terminal andground determines the regulation loop gain characteristics.Common ground terminal.A parallel RC network connected to this terminal determines theswitching frequency.Soft start time constant. A capacitor is connected between thisterminal and ground to define the soft start time constant. Thiscapacitor also determines the average short circuit outputcurrent.Regulator output.2FEEDBACK INPUT3FREQUENCYCOMPENSATIONGROUNDOSCILLATOR456SOFT START7OUTPUT2/16THERMAL DATA

SymbolRth j-caseRth j-ambThermal resistance junction-caseThermal resistance junction-ambientParametermaxmaxValue4 50Unit°C/W°C/WELECTRICAL CHARACTERISTICS (Refer to the test circuit, Tj = 25 °C, Vi = 35V, unless otherwisespecified)

SymbolParameterTest ConditionsMin.Typ.Max.UnitDYNAMIC CHARACTERISTICS

VoVi∆ Vo∆ VoVref∆ Vref∆ TVdIomI7LISHη SVROutput voltage rangeInput voltage rangeLine regulationLoad regulationInternal reference voltage(pin 2)Average temperaturecoefficient of refer voltageDropout voltageMaximum operating loadcurrentCurrent limiting threshold(pin 7)Input average currentEfficiency Supply voltage ripplerejectionSwitching frequencyVoltage stability ofswitching frequencyTemperature stability ofswitching frequencyMaximum operatingswitching frequencyThermal shutdownjunction temperatureVi = 46VVo = Vref to 36VIo = 1AIo = 2.5AVref9 5 40 15105.14650305.2VVmVmVVVi = 10V to 40V Vo = Vref Io = 1AVo = VrefVi = 9V to 46VTj = 0°C to 125°CIo = 1AIo = 2AVi = 9V to 46VVo = Vref to 36VVi = 9V to 46VVo = Vref to 36V Io = 0.5A to 2AIo = 1A 2.53 0.4 3mV/°CV1.4 A 304.560AmAVi = 46V; output short-circuitf = 100KHzIo = 2A∆ Vi = 2Vrmsfripple = 100HzVo = Vref Vi = 9V to 46VVo = VrefVo = 12V 75 508556 % 115 %dBIo = 1A 85 1000.5KHz%f∆ f∆ Vi∆ f∆ TjfmaxTsdTj = 0°C to 125°CVo = Vref Io = 2A 1201 %150150 KHz°C 3/16ELECTRICAL CHARACTERISTICS (continued)

SymbolParameterTest ConditionsMin.Typ.Max.UnitDC CHARACTERISTICS

I1Q -I7LQuiescent drain current Output leakage current100% duty cyclepins 5 and 7 openVi = 46V0% duty cycle0% duty cycle 15 201mAmA 3040mASOFT START

I6SOI6SISource currentSink current 10050

V2 = 4.7VV2 = 5.3VV2 = 5.3VV2 = 4.7VV2 = 5.2VV3 = 1V to 3VI3 = 100µAI3 = 100µA 100100 461501502553.514070

V0.5 10 VµAµAµAdB180120µAµAERROR AMPLIFIER

V3HV3LI3SI-I3SOI2GvHigh level output voltageLow level output voltageSink output currentSource output currentInput bias currentDC open loop gainOSCILLATOR

-I5Oscillator source current 5 mA4/16CIRCUIT OPERATION (refer to the block diagram)The L4960 is a monolithic stepdown switching regu-lator providing output voltages from 5.1V to 40V anddelivering 2.5A.

The regulation loop consists of a sawtooth oscilla-tor, error amplifier, comparator and the outputstage. An error signal is produced by comparing theoutput voltage with a precise 5.1V on-chip refer-ence (zener zap trimmed to ± 2%).

This error signal is then compared with the sawtoothsignal to generate the fixed frequency pulse widthmodulated pulses which drive the output stage.The gain and frequency stability of the loop can beadjusted by an external RC network connected topin 3. Closing the loop directly gives an outputvoltage of 5.1V. Higher voltages are obtained byinserting a voltage divider.

Output overcurrents at switch on are prevented bythe soft start function. The error amplifier output isinitially clamped by the external capacitor Css and

allowed to rise, linearly, as this capacitor is chargedby a constant current source. Output overload pro-tection is provided in the form of a current limiter.The load current is sensed by an internal metalresistor connected to a comparator. When the loadcurrent exceeds a preset threshold this comparatorsets a flip flop which disables the output stage anddischarges the soft start capacitor. A second com-parator resets the flip flop when the voltage acrossthe soft start capacitor has fallen to 0.4V.

The output stage is thus re-enabled and the outputvoltage rises under control of the soft start network.If the overload condition is still present the limiterwill trigger again when the threshold current isreached. The average short circuit current is limitedto a safe value by the dead time introduced by thesoft start network. The thermal overload circuit dis-ables circuit operation when the junction tempera-ture reaches about 150°C and has hysteresis toprevent unstable conditions.

Figure 1. Soft start waveforms

Figure 2. Current limiter waveforms

5/16Figure 3. Test and application circuit

C6, C7: EKR (ROE)L1 = 150µH at 5A (COGEMA 946042)CORE TYPE: MAGNETICS 58206-A2 MPP N° TURNS 45, WIRE GAUGE: 0.8mm (20 AWG)Figure 4. Quiescent draincurrent vs. supply voltage (0%duty cycle)Figure 5. Quiescent draincurrent vs. supply voltage(100% duty cycle)Figure 6. Quiescent draincurrent vs. junction tem-perature (0% duty cycle)

6/16Figure 7. Quiescent draincurrent vs. junction tem-perature (100% duty cycle)

Figure 8. Reference voltage(pin 2) vs. Vi

Figure 9. Reference voltageversus junction temperature(pin 2)

Figure 10. Open loop fre-quency and phase respondeof error amplifier

Figure 11. Switching fre-quency vs. input voltage

Figure 12. Switching fre-quency vs. junction tem-perature

Figure 13. Switching fre-quency vs. R2 (see test circuit)

Figure 14. Line transientresponse

Figure 15. Load transientresponse

7/16Figure 16. Supply voltageripple rejection vs. frequency

Figure 17. Dropout voltagebetween pin 1 and pin 7 vs.current at pin 7Figure 18. Dropout voltagebetween pin 1 and 7 vs.junction temperature

Figure 19. Power dissipationderating curve

Figure 20. Efficiency vs.output currentFigure 21. Efficiency vs.output current

Figure 22. Efficiency vs.output current

Figure 23. Efficiency vs.output voltage

8/16APPLICATION INFORMATION

Figure 24. Typical application circuit

C1, C6, C7: EKR (ROE)D1: BYW80 OR 5A SCHOTTKY DIODESUGGESTED INDUCTOR: L1 = 150µH at 5ACORE TYPE: MAGNETICS 58206 - A2 - MPP N° TURNS: 45, WIRE GAUGE: 0.8mm (20 AWG), COGEMA 946042U15/GUP15: N° TURNS: 60, WIRE GAUGE: 0.8mm (20 AWG), AIR GAP: 1mm, COGEMA 969051.Figure 25. P.C. board and component layout ofthe Fig. 24 (1 : 1 scale)

Resistor values forstandard output voltagesVo12V15V18V24VR34.7KΩ4.7KΩ4.7KΩ4.7KΩR46.2KΩ9.1KΩ 12KΩ 18KΩ9/16APPLICATION INFORMATION

Figure 26. A minimal 5.1V fixed regulator; Very few component are required

* COGEMA 946042 (TOROID CORE) 969051 (U15 CORE)** EKR (ROE)Figure 27. Programmable power supply

Vo = 5.1V to 15VIo = 2.5A maxLoad regulation (1A to 2A) = 10mV (Vo = 5.1V)10/16APPLICATION INFORMATION (continued)

Figure 28. Microcomputer supply with + 5.1V, -5V, +12V and -12V outputs

11/16APPLICATION INFORMATION (continued)

Figure 29. DC-DC converter 5.1V/4A, ± 12V/2.5A; a suggestion how to synchronize a negative output

L1, L3 = COGEMA 946042 (969051)L2 = COGEMA 946044 (946045)D1, D2, D3 = BYW80Figure 30. - In multiple supplies several L4960s can be synchronized as shown

12/16APPLICATION INFORMATION (continued)Figure 31. Regulator for distributed supplies

MOUNTING INSTRUCTION

The power dissipated in the circuit must be removedby adding an external heatsink.

Thanks to the Heptawatt package attaching thehetsink is very simple, a screw or a compressionspring (clip) being sufficient. Between the heatsink

and the package it is better to insert a layer of silicongrease, to optimize the thermal contact, no electri-cal isolation is needed between the two surfaces.

Figure 32. Mounting example

13/16DIM.ACDD1EE1FF1GG1G2H2H3LL1L2L3L4L5L6L7L9MM1V4DiaMIN.mmTYP.2.41.20.350.70.62.344.887.4210.0516.721.2422.272.615.162.554.833.652.545.087.6216.914.9221.5422.522.815.56.350.22.85.08MAX.4.81.372.81.350.550.970.80.92.745.287.8210.410.417.121.8422.771.29315.86.6MIN.inchTYP.0.0940.0470.0140.0280.0240.0950.1930.2950.3960.6570.3860.8770.1020.5940.2360.1000.2000.3000.6680.5870.8480.8910.1100.6100.2500.0080.1100.200MAX.0.1890.0540.1100.0530.0220.0380.0310.0350.1050.2050.3070.4090.4090.6730.8600.8960.0510.1180.6220.2600.1200.2100.152OUTLINE ANDMECHANICAL DATA3.050.1005.330.19040˚ (typ.)3.850.144Heptawatt VLEL1M1ACD1L5L2L3EE1FVVDMH2V4L9H3H1Dia.GG1G2FL7L6L4H2F1HEPTAMEC14/16DIM.ACDD1EFF1GG1G2H2H3LL1L2L3L5L6L7L9DiammMIN.TYP.MAX.4.81.372.41.20.350.62.414.917.4910.0514.24.415.85.12.615.164.443.653.850.144315.86.60.1020.5940.2362.545.087.622.81.350.550.80.92.675.217.810.410.40.3960.0950.1930.2950.0940.0470.0140.024MIN.inchTYP.MAX.0.1890.0540.1100.0530.0220.0310.0350.1000.2000.3000.1050.2050.3070.4090.4090.5590.1730.6220.2010.1180.6220.2600.1750.152OUTLINE ANDMECHANICAL DATAHeptawatt H15/16Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences ofuse of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is grantedby implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this publication are subject tochange without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are notauthorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.

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