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Maxim > Design Support > Technical Documents > Reference Designs > Automotive > APP 4329
Keywords: cold crank, boost, step up
REFERENCE DESIGN 4329 INCLUDES: Tested Circuit Schematic BOM Test Data
How to Use the MAX15005 Current-Mode Controller
as a Boost Circuit for an Automotive Cold-Crank
Condition
Dec 11, 2008
Abstract:
This reference
design shows how to use a MAX15005 automotive power-supply controller as a boost
circuit to maintain a constant voltage during an automotive cold-crank condition.
Introduction
When an automotive engine remains in a cold climate or is subjected to freezing temperatures for a long time,
the engine oil becomes very viscous. In cold temperatures the battery’s internal resistance also increases from
its normal value. If the engine is started during that time, the starter motor needs more torque, which draws
more current from the battery. Due to transients in the current requirement and high-series resistance, the
battery voltage can drop as low as 2.5V. This is known as the cold-crank condition in automotives.
The MAX15005 is a current-mode controller that operates from 4.5V to 40V. The device can manage cold-
crank conditions and a load-dump condition as well. Once powered, the MAX15005 operates down to 2.5V,
thus accommodating a further drop in the battery voltage.
This reference design shows a solution for a cold crank in automotive applications. The design includes the
complete schematic, bill of materials (BOM), efficiency measurements, and test results.
Specifications and Design Setup
The design uses the following specifications:
Input voltage: 2.5V to 18V
Output voltage: 12V
Output current: 1A
Output ripple: ±0.6V
Input ripple: ±15mV
Efficiency: 75% with cold crank > 90% for normal operation
Switching frequency: 200kHz
The schematic for the above specifications is shown in Figure 1.
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