BQ27Z746: No existance of CHG FET Gate-source Resistor

JEONGWOO KIM

Part Number: BQ27Z746
Other Parts Discussed in Thread: BQ28Z620

Tool/software:

Hi Ti Team,

I have a question about FET's gate-source resistor.

I looked at the reference circuit of the BQ27z746 and I am curious why there is no resistance between the gate-source of the CFET.

Some TI BMS IC (with protection function, BQ28z620) has this resistor, but it seems that the BQ27z746 does not have it.

Why is that so?

Thanks.

Alex.

7 months ago

0 Jonny 7 months ago

TI__Mastermind 20251 points

Hello Alex,

Are you referring to the 10M ohm resistor?

Regards,

Jonny.

0 JEONGWOO KIM 7 months ago

Prodigy 50 points

Hello Jonny.

Yes, I want to know why10M ohm resistor is not necessary on CFET circuit on BQ27z746.

Thanks.

ALex.

0 Jonny 7 months ago in reply to JEONGWOO KIM

TI__Mastermind 20251 points

Hello Alex,

The purpose of the 10Mohm resistor between the DSG pin and P+ is to prevent current flow into the charge pump. This same resistor can be applied on the CHG pin, but is not necessary.

Regards,

Jonny.

0 JEONGWOO KIM 7 months ago in reply to Jonny

Prodigy 50 points

Hello Jonny.

please tell me why the 10M resistor is not necessary on the CHG Pin, on the other hand other BMS ics do need the 10M ohm on the CHG pin.

Regards,

Alex.

0 Jonny 7 months ago in reply to JEONGWOO KIM

TI__Mastermind 20251 points

Hello,

The reason why the 10M ohm is present on the DSG FET is because the DSG FET is exposed to more transient load behaviors. For instance, removing the charger and changing load, this mainly affects the DSG FET. Also, it has the benefit of preventing leakage current from flowing through the DSG pin.

Whereas, the CHG pin mainly has the battery attached and it is less likely to experience transient behaviors. You can still install the 10M ohm for extra safety if desired.

Regards,

Jonny.

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BQ27Z746: No existance of CHG FET Gate-source Resistor