LM3485 failed at -40 degrees.

Hi

I'm Jun, Hardware engineer in South Korea.

I designed Power supply using part LM3485.

The Control Board is composed of the motor, MCU, UART...  

See the Below Block diagram

My Operating Tempeature Spec is -40 ~ +70 degrees.

This Control Board operates normally at +25 degrees and +70 degrees.

But the Control Board faild at -40 degrees.

The condition is below table

1) Load current(at +6.3V) is 40mA at No operates Motor.

2) Load current(at +6.3V) is 40mA+200mA at operates Motor. The Motor current is 190 ~ 210mA.

The Motor does not operate always. Opearting time is 10 seconds and No operate time is 30 ~ 60 seconds.

Operating Procedure is

1) Turn on the power

2) Check the current concumption

3) Check RS422 communication with PC.

4) Set the command "Motor ON"

 => "Power Short " occur immediately and Dead LM3485 & DRV8832.

The Circuit of LM3485

The Circuit of DRV8832.

I replaced C10 10uF => 470uF and it tested but Control Board faild.

I need TI help.

Thank you