TUTORIALS 4329

How to Use the MAX15005 Current-Mode Controller as a Boost Circuit for an Automotive Cold-Crank Condition


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.

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

The BOM for this reference design is given in Table 1.

Table 1. Bill of Materials
Designator Value Description Part Footprint Manufacturer Quantity
C1 10µF/25V Capacitor GRM32DR71E106KA12L 1210 Murata® 1
C2 1µF/25V Capacitor GRM219R71E105KA88D 805 Murata 1
C3 10µF/25V Capacitor GRM32DR71E106KA12L 1210 Murata 1
C4, C6 1µF/16V Capacitor GRM188R71C105KA12D 603 Murata 2
C5 150pF Capacitor GRM1885C1H151JA01D 603 Murata 1
C7 100pF Capacitor GRM1885C1H101JA01D 603 Murata 1
C8, C9 330pF Capacitor GRM1885C1H331JA01D 603 Murata 2
C10 10nF Capacitor GRM188R71H103KA01D 603 Murata 1
C11 0.1µF Capacitor GRM188R71H104KA93D 603 Murata 1
D1 30V/500mA Schottky Schottky diode MBR0530T1 SOD123 On Semiconductor® 1
D2 30V/500mA Schottky Schottky diode MBR0530T1 SOD123 On Semiconductor 1
D3 40V/2A Schottky Default diode B240 SMB Diodes Incorporated 1
L 10µH Inductor IHLP-4040DZER100M01 IHLP-4040EZ Vishay® 1
Q 30V, 17A n-channel MOSFET n-channel MOSFET SI7386DP Power PAKSO-8 Vishay 1
R1 61.9K Resistor SMD 1% Resistor 603 Vishay 1
R2, R12 100K Resistor SMD 1% Resistor 603 Vishay 2
R3 604Ω Resistor SMD 1% Resistor 603 Vishay 1
R4 4.7 Resistor SMD 1% Resistor 603 Vishay 1
R5 17.8K Resistor SMD 1% Resistor 603 Vishay 1
R6 100 Resistor SMD 1% Resistor 603 Vishay 1
R7, R8 0.07Ω/1W Resistor LRCLR2010LF01R070J 2010 IRC 2
R9 20K Resistor SMD 1% Resistor 603 Vishay 1
R10 137K Resistor SMD 1% Resistor 603 Vishay 1
R11 15.6K Resistor SMD 1% Resistor 603 Vishay 1
R13 10.5K Resistor SMD 1% Resistor 603 Vishay 1
U1 4.5V to 40V input, automotive flyback/boost/SEPIC, power-supply controller PWM controller MAX15005BAUE+ TSSOP-16 Maxim 1

Performance Data

The efficiency vs. load current plots for this design are given in Figure 2. Input voltage was the test parameter.

Figure 2, Load current vs. converter efficiency.
Figure 2. Load current vs. converter efficiency.

Converter output voltage and load current are shown in Figure 3 and Figure 4 with VIN = 2.5V and VIN = 11V, respectively.

Figure 3. Converter output voltage and load current with VIN = 2.5V. CH1: output voltage; CH2: MOSFET gate voltage; CH3: output current.
Figure 3. Converter output voltage and load current with VIN = 2.5V.
CH1: output voltage; CH2: MOSFET gate voltage; CH3: output current.


Figure 4. Converter output voltage and load current with VIN = 11V. CH1: output voltage; CH2: MOSFET gate voltage; CH3: output current.
Figure 4. Converter output voltage and load current with VIN = 11V.
CH1: output voltage; CH2: MOSFET gate voltage; CH3: output current.

Related Parts
MAX15005 Free Sample
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APP 4329:
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