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BQ27426: Registers Reset

Allan Fan
Expert 6000 points
Part Number: BQ27426

Hi expert,

Customer found the registers would be cleaned and become default after entering then exiting sleep mode. Not sure when the POR happened cause they read out the [ITPOR] after exiting sleep.   

bq27426_進入shipping mode前後資料差異_240227.pdf

We found the Vdd would drop when entering sleep but not for BAT. After they added another 10uF on the Vdd, the reset issue was resolved.  

TRM mentioned POR condition is REGIN > Vregin but I don't see BQ27426 has REGIN. 

 

Q1: what's the POR condition for BQ27426?

Q2: is it expected that the Vdd drop when gauge entering sleep mode? 

Thanks,

Allan

  • 0
    TI__Guru 52996 points

    The bq27426 relies on the capacitor on VDD during sleep. It must be 2.2uF at 1.8V and over temperature. A lot of nominal 2.2uF capacitors are de-rated (a typical 2.2uF capacitor in 0201 package may have around 1uF effective capacitance at 1.8V over temperature) and won't work.

    The gauge will reset (POR), if the voltage on VDD drops below approx. 1.65V (this varies between parts) so if the VDD capacitor is too small (e.g. derated to 1uF), the voltage on VDD will drop below this threshold during sleep which resets the gauge.

    You'll see a sawtooth waveform on VDD during sleep (normal behavior). The nadir of this waveform must not drop below approx. 1.65V and this is controlled by the size of the capacitor on VDD.

  • 0 in reply to Dominik Hartl11
    Prodigy 10 points

    Hi Expert,

    we found that integrated LDO VDD would drop deeply and then fuel gauge reset if I2C bus CLK ,DAT are from logic high to low during fuel gauge in sleep mode.But fuel gauge would not reset if I2C bus always keep low during fuel gauge in sleep mode,can you further explain for this,thanks.

  • 0 in reply to ShaoWei Chen
    TI__Guru 52996 points

    Please make sure that nothing other than the 2.2uF capacitor and optionally a 1.8MOhm resistor to BIN is connected to VDD. You can't use this as a pull-up rail for I2C for example (which if you did could explain why you see that massive drop on VDD).