LM7481-Q1: B2B bidirectional switch

Sherry Liang

Part Number: LM7481-Q1
Other Parts Discussed in Thread: INA302-Q1

Dear team,

My customer has a special requirement for 12V BMS system. The source of Q1 connects to 12V Li-ion battery, and the source of Q2 connects to system load. When the system works normally, the current direction is from 12V BAT to Load; when the Li-ion battery needs to be charging, the current direction is from Load to 12V BAT. Every direction needs to include reverse polarity protection, so we are considering to use two LM7481-Q1 to drive one B2B switch together. We will use EN pin to control the direction, and only one LM7481-Q1 is working in each direction. My questions are as below,

1. Is below architecture feasible?

2. When the direction is switched, how long does our device take to switch?

Thanks & Best Regards,

Sherry

over 2 years ago

0 Praveen GD over 2 years ago

TI__Guru 57737 points

Hi Sherry,

This architecture will not be feasible. This is because when one LM74810-Q1 device tries to pull the FET gates high, the other controller will try to pull the gates low. As the sink current of the controller is > the source currents, the FET gates will always stay low.

I understand that you are trying to same power path for charging and discharging the FETs. Let me think and get back to you of any smart way to do this. Meanwhile, can you let me know if any other features are required in this application apart from,

Input reverse polarity for battery
Load, Power path ON/OFF control

0 Sherry Liang over 2 years ago in reply to Praveen GD

TI__Genius 10255 points

Hi Praveen,

Thanks for your reply!

They also need overcurrent protection function.

Thanks & Best Regards,

Sherry

0 Praveen GD over 2 years ago in reply to Sherry Liang

TI__Guru 57737 points

Hi Sherry,

You will need to have separate power paths (FETs + Controller) for charging the battery and battery suppling load. Over current protection can be achieved with LM7481-Q1 by using INA302-Q1 + Current sense resistor as shown below.