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BQ25700A: Switching MOSFETs

Part Number: BQ25700A
Other Parts Discussed in Thread: EV2400, CSD17551Q3A, CSD17308Q3, BQ24725A


Taking my first steps with BQ25700A.

After running BQ25700A-EVM with EV2400, I printed a proto board.

I had a few CSD17308Q3 left from a previous buck only charger (BQ24725A) series, and after comparing CSD17551Q3A and CSD17308Q3 datasheets, I chose this last one for the proto.

Rds_on are similar, but Qg and Qgd are much lower with CSD17308Q3. So switching losses should be lower, right?

Did TI choose CSD17551Q3A for the BQ25700A EVM instead of CSD17308Q3 because it's newer? Apart from a lower Vgs for CSD17308Q3 (+10/-8V instead of +20/-20V), I don't understand why CSD17551Q3A should be more fit for this application.

Can someone tell me if I made a wrong choice, and if so, why?

If my choice is OK, where can I get some advice for placing vias under the thermal pad for heat conduction? Same guidelines as for CSD17551Q3A? No info for thermal vias on CSD17308Q3 datasheet.

Thank you.


  • Matthieu,

    The switching loss is lower for lower gate charge. The gate charge is also a trade off of the switching loss and the ringing due to the parasitic parameters including the trace inductance. I think you can use the MOSFET you have and find out whether the performance can meet your design requirements. The two MOSFETs are P2P compatible and you can exchange the FETs on the same PCB board.

    Both MOSFETs have the same package; you can apply the same thermal vias placement rule.
  • Hello Eric,

    Thank you for your answer.

    Indeed, if the gate signal rings above 10V I'm in troubles.