BQ34Z651: Soft starting (reducing di/dt) on the discharge MOSFET

Will White

Part Number: BQ34Z651

(A quick, albeit belated, THANK YOU to Batt--the problem(s) behind my original questions to you were identified, as well as fixes for them.)

Is there a soft-start for the CHG and DSG gate drive outputs that can be configured with ROM settings or a recommended circuit?

If not, how critical is the 3.01M feedback resistor in the discharge MOSFET gate drive circuit, especially if I add a (much smaller) series resistor and capacitor as feedback to further soften the edge at the DSG pin?

Best Regards,

Will

over 6 years ago

0 Onyx Ahiakwo over 6 years ago

TI__Guru* 76230 points

hi Will,
What is the reasoning why you would want to do that? When the device is needed for the safety features such as short circuit, it is required that the gate drive is able to turn off the fets as quickly as possible. You can do what you want with the drive circuit to reduce or increase the slew rate, but know that this will come at a cost of reducing the reaction speed of the device

thanks
Onyx

0 Will White over 6 years ago in reply to Onyx Ahiakwo

Prodigy 40 points

Hi Onyx,

I am seeing an 80A inrush current because of the input capacitance of the power supply we have to use is multiplied by a 12V dV/ 40 microsecond dt that happens as a result of the edge rate of the DSG pin. There is a very good chance that the discharge path of our battery module will have larger capacitive loads than this. Regarding the reference design's short-circuit response time, how quickly does it turn off the FETs?

Best Regards,
Will

0 Onyx Ahiakwo over 6 years ago in reply to Will White

TI__Guru* 76230 points

pls see the data sheet. The turn off speed will depend on the fets capacitance and the series resistance.

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BQ34Z651: Soft starting (reducing di/dt) on the discharge MOSFET