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BQ2970: Determining FET RDSon choice

Nicholas Carley
Expert 8215 points
Part Number: BQ2970
Other Parts Discussed in Thread: CSD83325L, BQ2980

I’m curious about the FET choice because our over-current thresholds are going to be very low (250-350mA). I originally picked a small FET (CSD83325L) to start and with 20mΩ Rds,on we end up with a 5mV or so voltage threshold (outside the trimmable range)

Would you suggest picking a FET with higher resistance or could we do something like add an 0201 sized resistor in series with the FET to increase the effective Rds,on?

Also, how long does it take to get a custom factory programmed part?
Will we be better off sizing Rds,on (perhaps with the series R) to match a catalog device?

Thanks,
Nick

  • 0
    TI__Expert 7035 points

    Hi,

    If accuracy is really important to this project, I would recommend using the BQ2980 instead. It features high side FETs, but also uses a sense resistor to calculate the over current thresholds, so it is more accurate and easier to configure. If low-side FETs are a requirement, then I would recommend picking a FET with much higher resistance. 

    Custom programmed parts do have a minimum revenue requirement, and I am not sure we are currently taking requests for the 2970. You would be much better off finding the correct FET.