BQ25703A: BQ25703A only with Buck FETs

Fabian Luttenberger

Part Number: BQ25703A
Other Parts Discussed in Thread: CSD17579Q3A, BQ24773

I am already sucessfully using bq25703a with 12V input. I now want to change my design for 20V adapter input with max. 1.5A. Cell config is 4s (li-ion). I have a couple of questions:

For my application I won't need the boost converter. Is it possible to omit boost converter FETs?
Due to low current, I would like to use only one FET type. Is it possible to use CSD17579Q3A as buck FET and also as Battery FET?
For my application with only buck, bq24773 would also be an option. However, it seems to be an "older version" of the bq25703a, are there any drawbacks?

Thanks in advance

over 5 years ago

0 Tiger Zhou over 5 years ago

TI__Mastermind 32965 points

1. No, we can't omit boost converter FETs. These FETs are needed during startup.

2. Battery FET needs P-FET. The other FETs are N-FET.

3. BQ24773 is another family of charger, other than BQ25703A. BQ25703A accepts a wide range of input sources. You are fine to use BQ24773.

0 Fabian Luttenberger over 5 years ago in reply to Tiger Zhou

Prodigy 235 points

Thank you for clarification.

For BQ25703a: If I change FETs and inductor to smaller ones for lower current, does that mean I also have to adapt the RC compensation network? Or can I leave it as it is in reference schematic?

0 Tiger Zhou over 5 years ago in reply to Fabian Luttenberger

TI__Mastermind 32965 points

If you stick with the same inductance, you don't need to change the RC compensation network. Otherwise, the RC needs to be adjusted accordingly.

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BQ25703A: BQ25703A only with Buck FETs