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BQ21040 Operation at -40C

Antonio Fadhel
Genius 9410 points
Other Parts Discussed in Thread: BQ21040

Hi Team,

The BQ21040 disables charging at <=0C per the TS section of the datasheet. However, the recommended min operating temp for the IC is 0C. Can you please confirm that charge will predictably remain disabled at temps down to -40C and resume at >0C? This is what is described on the TS section, but need confirmation since it is outside the recommended temp range.

Any characterization data, if available, would be very helpful.

Thanks,

Antonio

  • 0
    TI__Genius 11480 points
    Hi Antonio,

    Charge will remain disabled as long as the voltage at the TS pin is greater than ~1250 mV. If using one of the recommended thermistors, that will correspond to the temperature of 0 C.

    If you would like to add redundancy, you can also pull TS to GND to disable the IC at these temperatures.
  • 0 in reply to David Wiest Jr
    TI__Genius 9410 points
    Hi David,

    At ~-10C, the IC is expected to lower the TS current in order to avoid entering TTDM. Wouldn't this cause the TS pin voltage to drop below the 1250mV threshold? Does the IC still force charge disable in this case?

    Thanks,
    Antonio
  • 0 in reply to Antonio Fadhel
    TI__Genius 11480 points

    Antonio,

    Here  is some bench data  regarding TS Pin voltage, resistance at RTS, and the current sourced at RTS. I  used the resistance values from the  thermistor recommended in  the datasheet (Semitech 103AT-2). You can see  how  the current folds back to  keep the TS pin voltage below Vttdm.

    R(ts) | Thermistor equivalent temp | TS voltage | calculated source current


    24.32k         | 0 deg     | 1.24 V | (calculated 51 uA)

    40.056k       |               | 1.463 V | (calculated 36.5uA)

    47.9k           |               |  1.469 V | (30.7 uA)

    188.5k         | -40 deg  | 1.492 V | (7.8uA)

    So, the sourced current doesn't immediately fold back to 5uA as it appears  in the datasheet. it will reduce the current to maintain ~1.5V at TS. This will keep the charger disabled for all cold temperatures