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BQ24193: Do not understand REG09 values

Southern Engineering
Intellectual 715 points
Part Number: BQ24193

Hi,

We are currently seeing problems to charge in RT, at least with some units. Investigating what might be the reason we read REG09. Typically for those units we then see REG09 = 0x95 or 0x85 for the first read, followed by 0x05 for repeated readings. My understanding is that that means the charger is seeing the battery as 'cold', in turn meaning <0 degrees C with default TS resistor values (which we are using). Measuring the NTC resistance at the battery TS terminal I get 9.6 kOhm, so it seems to be reporting RT, while cold would be much higher.

Question 1: Would you interpret 0x05 differently?

Trying to make sense of this result I asked a colleague what he was seeing on his units, as a reference. He is seeing 0x37, which is not even defined in the datasheet.

Question 2: Does 0x37 mean something? 

Thanks!

  • 0
    TI__Guru 57541 points

    Hi,

    1.Yes, REG09=05 indicates TS cold.

    2. REG37 indicates REG09[5:4]=11, i.e. Charge Safety Timer Expiration.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Intellectual 715 points

    Hi,

    Just adding that we found the reason for this odd behavior. Turns out it was rather trivial in the end. REG09 was reporting Cold (0x85) due to a bad battery connector that in some cases did not provide a good connection to the battery NTC. The voltage divider at the TS pins therefore saw the NTC as open, generating a voltage of ~4.5V, which translated into Cold temperature range.