BQ76952: BQ76952 BACK TO BACK COMMON SOURCE FET DRIVE

Fikret Yildirim

Part Number: BQ76952

Hi;

We want to use BQ76952 AFE IC for our teeam design. We are thinking low side back to back common source mosfet for CHG and DHG vet . We will use DCHG and DDHG pin with mosfet driver for low side control . We dont use isolated driving because isolating circuit power consuption very high. So, We want to use low side common draim . But in our design graunding reference point(VSS) of BQ76952 is common source point of mosfets. We arent sure this design is safety or any fail in operation.

We are not sure if our design will work correctly. We are not sure if it will malfunction in any case of protection. 
We worry especially in case of short circuit. A partial part of the circuit we are considering designing is shown below. 
Can you help us with the regions circled in red and whether the circuit design is appropriate in this way?

over 2 years ago

0 Jose Couso over 2 years ago

TI__Mastermind 27321 points

Hello Fikret,

We always recommend to separate the high current path from low current path using either a Net-Tie or a zero 0-Ohm resistor. You can reference to the TIDA-010216 reference design where we showcase low side switching.

These two threads share good information about grounding concerns.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/968861/bq76920-can-charge-and-discharge-mosfets-be-connected-common-source

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/823905/bq76930-bat---or-pack---or-other-ways-to-connect-gnd

Regards,
Jose Couso

0 Fikret Yildirim over 2 years ago in reply to Jose Couso

Prodigy 105 points

Hello;

 I had previously reviewed the documentation and reference design on recommendation. However, in the recommended reference design, 
mosfets are used as common drains. In my design we want to use mosfets as a common source, and our common-source link will be our reference ground point. 
We are considering connecting the common-sources of mosfets with a 0 ohm resistor to the vc0 leg of Bq76952. 
In the BMS circuit we designed, there is a current limiting circuit connected in parallel to the charge mosfets .
 We want to drive all current limiting mosfets, charge discharge mosfets and AFE from taking a common graoun point . 
That's why we prefer a common source structure.What kind of problems does Afe's reference point being a common source cause?
 We would like to receive information about this subject.

0 Jose Couso over 2 years ago in reply to Fikret Yildirim

TI__Mastermind 27321 points

Hello Fikret,

The low side configuration requires an external FET driver. The internal driver only supports high side and this driver does not support common source configuration.

Now, in your application, it will depend on your external low side driver if it supports common source or not. We have not implemented this, so this would need to be tested.

Regards,
Jose Couso

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BQ76952: BQ76952 BACK TO BACK COMMON SOURCE FET DRIVE