LM5155: How to Deal with 54Vin

Besides, what is the purpose of the circuit here?

Dear Team, 

Will two 100kohm to divide the input voltage then connect to BIAS pin be the only solution?

Hi Kevin,

Thanks for reaching out with your questions.

First, if the input voltage of the application exceeds the maximum voltage rating of the BIAS pin there are two options. This is better than implementing a voltage divider with two 100 kOhm resistors.

1. Add a voltage clamp to the BIAS pin to keep the voltage below the absolute maximum voltage rating of the device

2. Supply the BIAS pin with an external rail. For example a 5V or 10V rail would work. This is assuming the application has an exteranl bias rail.

The circuit implemented by D21, R55 and C46 is a soft-start circuit. The simple idea is that if ramps the reference voltage to keep the output voltage for overshooting the target. To increase the soft-start time increase R55 or C46.

Please contact me directly if you have any questions.

Thanks,

Garrett

Dear Garrett

Thanks for the information.

I am not sure how to implement clamp circuit, do you mean Zener diode here?

BR

Kevin

Dear Garrett,

BTW, I would like to calculate 54Vin, 12Vo/5A efficiency.

But Webench's input voltage is set to 45V for maximum.

Can you calculate the efficiency here?

BR

Kevin