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INA233: INA233 current data occasionally becomes 0

RF Yan
Prodigy 10 points
Part Number: INA233

Hi,

I am testing my designed board using INA233 as battery charging monitor, shut R 2m Ohm, no RC filtering at IN+/IN-.

In the register setting, current LSB is 1mA/bit, no. of average is 1 (default) and Vshunt and Vbus conversion time is 1.1ms (default).

The PMBus host reads Vbus and Vshunt every 4s. (every minute 15 readings)

The load current (charging current) should be around 14A in our test, and Vbus (battery voltage) is around 25V (increasing slowly).

For current reading (through Vshunt), in most of the case it is around 14A and fluctuated between 13A to 15A ( the real charging current should not be fluctuated so much, so i think the reading is not accurate), and occasionally the current reading is 0. ( for value 0 reading, only 1 time in many readings, and after some time another 1 time).

For Vbus (battery voltage), it is not fluctuated too much since no need amplifier circuit inside INA233. But occasionally the Vbus reading is 0.(similar as current reading, random, may not be the same time when current reading is 0)

I believe the external battery charger output is correct, the charging current and voltage should be stable and impossible to be 0 in any time during charging phase.

So for the INA233 current reading (fluctuated and occasionally 0) or Vbus reading occasionally 0, is it because the no. of average setting is only 1, and conversion time setting is also not long?

If so, that means the register default value is not suitable for real accurate measurement.

And what is the recommended no. of average as well as conversion time?

Do you suggest to add RC filter at IN+/IN-?

Thank you.

  • 0
    TI__Mastermind 34250 points

    Hi RF,

    The variation in current, 2A (13A to 15A), corresponds to 4mV of delta in shunt voltage. INA233 will definitely do better regardless what register setting is being used. But you could vary the conversion time to see if it makes any difference. I doubt it will.

    Filtering is nice to have but not required. I don’t think it will resolve the main issue. The fact that both Vshunt and Vbus read zero occasionally is concerning. If you programmed the calibration register, you could read the current register to see if it returns zero when Vshunt reads 0.

    If current and shunt registers both return zero at the same time, I would start with solving this problem first. Specifically you may want to set up a scope that triggers on zero reading. The trigger can be created inside the reading loop and pass to an IO pin. You can also speed up the reading so that you don’t have to wait forever for the problem to occur.

    By capturing the I2C signals and Vbus voltage, we should be able to tell if INA233 is indeed returning 0V when Vbus is nonzero. I believe going through this process will help uncover the root cause.

    Regards, Guang