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bq34z100 pin2 Ven weirdness

Matt Palmer
Intellectual 450 points
Other Parts Discussed in Thread: BQ34Z100

So after running an initial lot of a battery with bq34z100 fuel gauge I have one piece that is displaying some weirdness, I have 0V on pin 2 Ven, checking dataflash its showing a battlow, and measuring 1.8V instead of the expected 7.4 (2S lion). all the dataflash and configuration looks identical to a good pack, what else could cause Ven to go low? or is there something else going on here?

  • 0
    TI__Guru 73830 points

    Matt,

     VEN is normally low, except when it pulses high periodically. The symptoms that you list sound like the voltage is not calibrated. I would check that and also check the voltage on the BAT pin.

    Tom

  • 0 in reply to ThomasCosby
    Intellectual 450 points

    I thought ven was to turn on/off the external divider for power savings? the design is identical to how it is in the data sheet with ven driving the gate of a n fet which is tied to a pfet which feeds the voltage divider, i have 900+ pieces that are fine but this one has ven low which is turning the voltage divider off which causes 0v at vbat calibration was done by averaging 15 plus golden samples  and using those values for programming the data flash

  • 0 in reply to Matt Palmer
    TI__Guru 73830 points

    You are correct. Voltage is applied to the BAT in when VEN pulses high, so I would check to see if VEN every pulses high. If it does not, then I would also check REGIN, CE and REG25 to make sure that they are the proper value. If they look okay, then there must be a defective bq34z100 or circuit connected to VEN.

    Also, while it is acceptable to use the averaging technique for calibrating current and temperature, we recommend calibrating the voltage on every device. The voltage measure accuracy is more critical.