Design a car cold start boost circuit using the MAX15005 current mode controller

Figure 1. Schematic of the MAX15005B boost converter for FSW = 200kHz.

introduction

When a car engine is exposed to cold climates or is exposed to prolonged freezing, the oil can become very viscous. At low temperatures, the internal resistance of a car battery will increase and be greater than the nominal internal resistance. If the engine is started in this condition, the starter motor will require more torque and draw more current from the battery. The large transient current and high series internal resistance will cause the battery voltage to drop to 2.5V. This situation is known as a cold start of the car.

The MAX15005 is a current-mode controller with an operating voltage range of 4.5V to 40V and can support both cold-crank and load-dump operating conditions. When powered on, the MAX15005's operating voltage can be reduced to 2.5V to meet battery voltage drop requirements.

The reference design provides an application solution for automotive cold start. This design includes a complete schematic, bill of materials (BOM), efficiency measurements and other test results.

Indicators and design solutions

The design adopts the following index specifications:

• Input voltage: 2.5V to 18V

• Output voltage: 12V

• Output current: 1A

• Output ripple: ±0.6V

• Input ripple: ±15mV

• Efficiency: 75% during cold start; greater than 90% under normal working conditions

• Switching frequency: 200kHz