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BQ25750: BQ25750 issue on commanding Batt FET by I2C

Francesco Paparella
Prodigy 60 points
Part Number: BQ25750

Tool/software:

Hello,

we have an issue with BQ25750...we cannot control the Batt FET consistently. We opening/closing the Batt FET by changing the value of bit EN_HIZ (bit 4) of the I2C message REG = 0x17. 

You can see from the attached picture that when we send the command REG 0x17 = 0 (Batt FET = open) and REG 0x17 = 4 (Batt FET=closed) multiple times. When the Batt FET is closed the system voltage Vsys overlaps with the battery voltage Vbat. After the 5th time, the BQ25750 stops working and the Batt FET cannot be commanded anymore. You can see from the oscilloscope that the battery current Ibat is in some kind of burst mode and the Batt FET is not commandable anymore.  

Also, the datasheet indicates that the Batt FET should close automatically when the battery voltage is present and the system voltage is low. However, this is not happening in our case and we need to send the I2C message REG 0x17.

Any suggestion?

thanks

Francesco Paparella