BQ76930: How to calculate the Rdrian in BQ76930 REGSRC circuit?

Brian Wang0

Part Number: BQ76930
Other Parts Discussed in Thread: TIDA-00449

Hi team,

I am writing to ask a question about how to calculate the Rdrian in BQ76930 REGSRC cirtui?

I noticed we have a detailed explanation of how the circuit works in BQ769X0 family Top 10 Considerations figure 14. If my understanding is correct, the voltage acorss Rdrian should be Vbat- VC5x-Vgsth. Then how we should determine the current limit value on this path?

Regards,

Brian

over 1 year ago

0 Andria McIntyre over 1 year ago

TI__Expert 8451 points

Hi Brian,

If you'd simply like to know what Rdrain value to use, both 100 Ohm and 200 Ohm resistors should work. The TIDA-00449 and EVM use these values. Information on typical and max current into the REGSRC pin can be found under electrical characteristics in the datasheet (BQ769x0 3-Series to 15-Series Cell Battery Monitor Family for Li-Ion and Phosphate Applications datasheet (Rev. I)).

More details and other questions about REGSRC circuitry can be found at this previous e2e post: (+) BQ76930: Is P channel Mosfet at Chg pin really mandatory? - Power management forum - Power management - TI E2E support forums. Hopefully this helps!

Best,

Andria

0 Luis H. S. over 1 year ago in reply to Andria McIntyre

TI__Mastermind 27490 points

Hello Brian,

The last response in this e2e thread may be useful:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/571588/bq76940-schematic-for-multiple-pack-configurations-and-removing-discharge-transistor

The current going through this resistor would be dependent on the current by drawn by the LDOs, in other words if the LDO is drawing 10-mA, there would be ~10-mA of current through Rdrain.

Best Regards,

Luis Hernandez Salomon