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bq78350 / Pre-charge current limiting resistor

Guru 11170 points
Other Parts Discussed in Thread: BQ78350, BQ78350-R1

Hi all,

Our customer use the bq78350 in their design.
We know bq78350 can set the pre-charge current by GUI or register.
They found a pre-charge current limiting resistor in document of EVM.

Our customer has questions as follow;
 - Current limiting resistor is required?
 - If not use the pre-charge, can they delete the FET and current limiting resistor for pre-charge from circuit?


Regards,
Nagai

  • If you use the precharge FET you should use a current limit resistor since the resistor is what will limit the current at the low cell voltage, the precharge FET is typically small and low power, and the gate control circuit is slow.

    If you don't need the pre-charge path you can remove the pre-charge resistor, the FET and the gate control components leaving the /PRECHG pin of the bq78350 open since it is an output.  Be sure to set the FET Options[PCHG_EN] and Pre-Charging Current parameters appropriately for the non-precharge FET configuration.  Check the documentation for the device version you are using (bq78350 or bq78350-R1) for more description of the parameters.

  • Thank you for reply.
    Your comment will be great help for our customer.