Maintaining Output Voltage Regulation During Automotive Cold-Crank with LM5118 Buck-Boost - Application Report SNVA741 - July 2015

Oct 13, 2026

Upload by Bintang

The standard 12 V automotive battery rail can fluctuate from 9 V to 16 V during normal operation, while transient events may drive battery voltage from 3 V to nearly 65 V. Cold-crank, when the battery energizes the engine starter, can drop to 3 V and challenges dc-dc converter design as ISO 7637-2 Pulse 4 and manufacturer test standards require robust performance. The LM5118 maintains output regulation down to 2.5 V and withstands load dump transients up to VIN max 75 V, using a single inductor for a smaller solution size.

LanguageEnglish

CategoryPresentations

FormatPDF

Pages4

Reading Time2 min

AccessFree to download

Abstract

Automotive battery rail voltage variation

Cold-crank conditions and test standards

LM5118 cold-crank regulation performance

Reference design and waveforms

Legal notice

Application Report SNVA741–July 2015 Maintaining Output Voltage Regulation During Automotive Cold-Crank with LM5118 Buck-Boost Garrett Roecker ABSTRACT The standard 12 V automotive battery rail can vary from 9 V-16 V during normal operation depending onload and charge. Under transients conditions battery voltages can range from 3 V to nearly 65 V. One of these extreme conditions is cold-crank. Cold-crank happens when the battery is trying to energize the starter of the engine and the battery voltage plummets to 3 V. Previously a small number of functions were required to operate during this condition, however automotive manufactures are requiring more features to endure cold crank in order to improve vehicle performance and operator comfort. With this range of input voltage and new standards, dc-dc converter design can be challenging. Cold-cranking conditions are out lined in ISO 7637-2 Pulse 4. Automotive manufactures tend to supply customized standards for cold-crank testing. Many manufacturer standards are very similar to the ISO standard, usually with varying time durations and voltage levels. Figure 1 shows an example of a coldcrank waveform. 12 V 6 V 3 V 0 V 5 ms 15 ms to 40 ms 50 ms 0.5 s to 20 s 5 ms to 100 ms Figure 1. Example Cold-Crank Waveform The LM5118 can maintain output regulation during a cold-crank event of input voltages down to 2.5 V. It can also endure events such as load dump where the voltage may exceed 65 V, being rated for VIN max of 75 V. Also as it uses a single inductor the solution size is smaller than that of a SEPIC or cascaded buck-boost topology. Figure 2 shows a LM5118 design that regulates the output at 5V and delivers 3A through a cold-crank event. This design also has the ability to withstand a load dump transient up to 42 V. The design can be found under reference ID PMP10681 . The reference design is a modified LM5118 orderable evaluation module. Figure 3 shows that even with a transition time of 1ms from 12 V to 2.5 V the output regulation is maintained. All trademarks are the property of their respective owners. SNVA741–July 2015 Maintaining Output Voltage Regulation During Automotive Cold-Crank with 1 Submit Documentation Feedback LM5118 Buck-Boost Copyright © 2015, Texas Instruments Incorporated [www.ti.com](www.ti.com) CH1: VIN 5V/div CH2: CH3: CH4: IL 5A/div VOUT(DC) VOUT(AC) 5V/div 500mV/div Figure 2. Cold Crank Waveform: (ΔVOUTMAX = 200 mV) CH1: VIN 5V/div CH2: CH3: CH4: IL 5A/div VOUT(DC) VOUT(AC) 5V/div 500mV/div Figure 3. Cold Crank Transition VIN 12 V to 3 V in 1ms (ΔVOUTMAX = 200 mV) 2 Maintaining Output Voltage Regulation During Automotive Cold-Crank with SNVA741–July 2015 LM5118 Buck-Boost Submit Documentation Feedback Copyright © 2015, Texas Instruments Incorporated [www.ti.com](www.ti.com) Figure 4. Test Board Schematic: Reference Design PMP 10681 SNVA741–July 2015 Maintaining Output Voltage Regulation During Automotive Cold-Crank with 3 Submit Documentation Feedback LM5118 Buck-Boost Copyright © 2015, Texas Instruments Incorporated IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems nece

FAQs

What causes the cold-crank challenge in a 12 V automotive system?

Cold-crank occurs when the battery tries to energize the engine starter, causing the battery voltage to plunge to about 3 V.

Which test standard is referenced for cold-crank conditions?

Cold-cranking conditions are outlined in ISO 7637-2 Pulse 4, and manufacturers often provide customized cold-crank testing standards similar to the ISO standard.

How does the LM5118 perform during cold-crank and load dump?

The LM5118 maintains output regulation during cold-crank events with input voltages down to 2.5 V, and it can endure load dump where the voltage may exceed 65 V (rated VIN max of 75 V).

Oct 13, 2026

Upload by Bintang