Maintaining Output Voltage Regulation During Automotive Cold-Crank with LM5140 Dual Synchronous Buck Converter

Application Report SNVA748–January 2016

TerryAllinder

Designing electronics to operate from a 12-V car supply is challenging. The 12-V battery supply voltage can range from 9-16V under normal operation depending on charge and load variation. However, the transient battery voltage range can be much wider. One of these conditions is cold-crank. Cold-crank occurs when the battery is trying to energize the starter-motor circuits on the internal combustion engine. Traditionally, only a few critical functions were required to ride through the cold-crank. Increasing car manufactures are making more features available through cold-cranks for a better driver experience and safety. The cold-crank profile is described by ISO 7637-2 (test pulse 4). Individual car manufacturers have similar cold-crank profiles with the supply rail dropping to 3 V or lower depending on the location of the load. An example cold-crank profile is shown in Figure 1. The actual voltage levels and time intervals are manufacturer specific.

Supply

12 V

6 V

3 V

15 ms to time 5 ms 40 ms 50 ms 0.5 s to 20 s 5 ms to 100 ms

Figure 1. A Representative (Cold-Crank) Test Profile for Car Supply with 12V Battery

To keep the safety and convenience functions such as navigation, entertainment, dashboard, LED break lights and headlights working through drops in the battery profile, the DC-DC converter supplying these loads must be able to maintain regulation even when the 12-V supply voltage drops below the required output voltage. The LM5140, a Dual Synchronous Buck controller, can maintain regulation on the 3.3V output even at supply voltages of 3.8 V, and on the 5.0 V output it can maintain output voltage regulation with the battery voltage dropping down to 5.5V. With an absolute maximum voltage rating of 60 V, it can survive load dump transients with ease. In addition, the LM5140’s oscillator can switch at 2.2 MHz reducing to size of the output inductor and filter capacitor providing small solution size. The LM5140 incorporates features to simplify the compliance with the CISPR and Automotive EMI requirements. The LM5140 has two selectable switching frequencies, 2.2 MHz and 440 kHz, Gate Drivers with Adaptive Slew Rate Control, and Interleaved (180 degree output of phase) operation of the two outputs.

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SNVA748–January 2016 Maintaining Output Voltage Regulation During Automotive Cold-Crank with 1 Submit Documentation Feedback LM5140 Dual Synchronous Buck Converter Copyright © 2016, Texas Instruments Incorporated www.ti.com The LM5140 Dual Synchronous Buck converter schematic is shown in Figure 3 with an operating input voltage range of 3.8 V to 42 V with the ability to withstand load dump transients up to 42 V. Figure 2 shows a cold-crank test condition. The converter maintains the output voltage even when the input supply voltage drops below 3.8 V.

Figure 2. VOUT Regulated at 3.3V with VIN 3.8V for 20ms (Load 4A)

2 Maintaining Output Voltage Regulation During Automotive Cold-Crank with SNVA748–January 2016 LM5140 Dual Synchronous Buck Converter Submit Documentation Feedback Copyright © 2016, Texas Instruments Incorporated www.ti.com

VIN VIN 4 - 42VDC VCC VIN VCCX VDDA L1 TP8 J2 VOUT2 VOUT1 ZX1 1 R39 S1A Assembly Note 2 15.0k 7447798360 1 4 2.2MHz 3.3V/5.0V

1715721 3 4 C40 47µF C7 C8 S1B C41 C39 1µF 1µF 2 3 0.1µF 10µF VIN

1 2 R34 VIN T1 1.0 PA2756NL C42 C43

J4 2.2µF R17 C23 1 0 0.1µF 2.2µF C11 C28 1040 SGND C19 J5 2.2µF 1 2.2µF C38 SGND 2.2µF

C12 D1 D2 C29 1040 C21 2.2µF 0.47µF 2.2µF 2.2µF PMEG6010CEJ,115 SGND PMEG6010CEJ,115 SGND SGND SGND

25 6 36 Q2 15 16 SQJ850EP-T1-GE3

7,8 5,6, C17 C24 R12 Q3

VIN

4 0.1µF 20 11 0.1µF 5,6, 7,8 HB1 VCC VCC HB2 SQJ850EP-T1-GE3

VCCX VDDA R19 10.0 4 ZX3 VOUT1 ZX2 Assembly Note VOUT2 L2 22 HO1 HO2 9 10.0 L3 Assembly Note 5.0V @ 5A MAX

1,2,3 3.3V @ 6A MAX MSS1038-152NLB R13 23 8 R20 MSS1038-252NLB HOL1 HOL2 1,2,3 R5 0 0 R29 21 SW1 SW2 10 TP1 0.006 0.009 TP13 C9 R14 18 13 R21 C31 R9 LO1 LO2 R25 DNP DNP 7,8 5,6, 10.0 10.0 5,6, 7,8 DNP DNP R4 R6 4 19 12 4 R28 R30 C1 C2 C3 C4 1.40k LOL1 LOL2 1.40k C34 C35 C36 C5 0 49.9 0.1µF R15 R22 0.1µF 49.9 0 C33 C37 DNP82µF 82µF 82µF D3 D4 82µF 82µFDNP82µF

47µF R7 R8 C10 C30 R26 R27 47µF 0.1µF

B170-13-F 17 14 0.1µF C6 DNP 10.0 PGND1 PGND2 10.0 DNP C32 DNP100 DNP100 1000pF DNP100 DNP100

B170-13-F 1,2,3 Q1 U1 Q4 1,2,3

1000pF 27 4 SQJ850EP-T1-GE3 CS1 CS2 SQJ850EP-T1-GE3 33pF 33pF TP2 LM5140RHA TP14 26 VOUT1 VOUT2 5 SGND 24 7 SGND VOUT2 VOUT1 PG1 PG2 R10 R24 31 EN1 EN2 40 DNP1.00 DNP1.00 SYNC_OUT 38 39 EN1 SYNC_IN SYN_IN SYN_OUT EN2 TP9 R1 R37 R38 R31 C44 29 COMP1 COMP2 2 C45 10.0 100k DNP82µF DNP82µF 100k 10.0 J1 28 3 VDDA J10 EN1 FB1 FB2 EN2 2 VDDA SGND SGND 1 1 TP5 30 SS1 SS2 1 TP10 2 S2A S3A

5-146261-1 1 6 ILSET RES OSC AGND DAP DEMB 1 6 5-146261-1 R2 SGND SGND R32

43.0k 34 32 37 35 33 43.0k S2B S3B PG1 ILSET PG2 2 5 2 5 TP3 TP11 R16 R18 S2C R11 6.49k 10.0k R23 S3C R33 3 4 10.0k C13 C15 C16 C18 C20 C22 C25 C27 10.0k 3 4 20.0k R3 0.01µF 22pF 0.068µF 0.01µF 0.01µF 0.068µF 47pF 0.01µF 20.0k PG1 BIAS C14 C26 PG2 BIAS 0.01µF 0.01µF SGND FB1 - VDDA = 3.3V FB2 - VDDA = 5.0V SGND FB1 - RDIV = 3.5V J6 FB2 - RDIV = 5.5V SGND 1 SGND FB1 - GND = 5V FB2 - GND = 1.8V 1040 VDDA VIN TP6 TP7 VCC VDDA VDDA VIN VDDA SYNC_IN ILSET SGND S5A S7 S4 S8 S9 R35 1 4 3 S6A 1 1 1 1 4 0 PG1 BIAS 2 EN2 2 2 2 R36 S5B SYNC_IN ILSET EN1 DNP R40 0 2 3 1 S6B 3 3 R41 3 2 3 OSC - VDDA = 2.2MHz 1.00k PG2 BIAS CJS-1201TA 1.00k OSC - GND= 460KHz CJS-1201TA CJS-1201TA CJS-1201TA DEMB - GND = DEMB SGND SGND SGND SGND SGND SGND DEMB - VDDA = FPWM Figure 3. LM5140 2.2MHz EVM Schematic

SNVA748–January 2016 Maintaining Output Voltage Regulation During Automotive Cold-Crank with 3 Submit Documentation Feedback LM5140 Dual Synchronous Buck Converter Copyright © 2016, Texas Instruments Incorporated www.ti.com References ISO 7637-2: Road vehicles - Electrical disturbances from conduction and coupling -Part 2: Electrical transient conduction along with supply lines only. LM5140 Wide Input Range Dual Synchronous Buck Controller Cranking Simulator Reference Design for Automotive Applications (PMP7233)

4 Maintaining Output Voltage Regulation During Automotive Cold-Crank with SNVA748–January 2016 LM5140 Dual Synchronous Buck Converter Submit Documentation Feedback Copyright © 2016, Texas Instruments Incorporated www.ti.com Revision History

Revision History DATE REVISION NOTES January 2016 * Initial release.

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