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BQ25672: Hi-Z mode and the IBAT current sense amp

Nicholas Carley
Genius 9925 points
Part Number: BQ25672
Other Parts Discussed in Thread: BQ25628E, BQ25622E, BQ25638

Tool/software:

When in Hi-Z mode REGN LDO is turned off, is the IBAT current sense amplifier powered during HI-Z mode?

If it is powered, how much quiescent current does the IBAT CSA use during HI-Z mode? Should we manually disable it?

  • 0
    TI__Guru**** 166696 points

    Hi Nicholas,

    The ADC does not read discharge current in HiZ unless REG0x14[5]=1 (i.e. CSA is off).  The CSA Iq is approximately 150uA but it is insignificant compared to the >600uA the ADC pulls when enabled.  Also, running average does not function correctly when REG0x14[5]=1.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 350 points

    Thanks Jeff. But we can switch EN_IBAT on, turn on ADC, read ADC, switch off ADC & EN_IBAT. Is there a setup time required between enabling EN_IBAT and reading the ADC?

    Are we also able to read VBAT & VSYS ADC when in battery only mode?

  • 0 in reply to Peter Schmuckal
    TI__Guru**** 166696 points

    Hi Peter,

    The typical conversion times vs bit setting is below:

    We found later that the 12-bit measures too low so I only recommend using the 13-bit.  For 1 short running average of one channel, then the host needs to wait at least 12ms typical before reading the ADC register.

    Also, the datasheet does not spec absolute ADC accuracy.  The ADC is meant to only provide a reasonableness check.

    And yes, all of the voltage channels are available in HiZ mode.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 350 points

    Ok thanks. Yes I saw the conversion times. My question was more concerned with in a system where EN_ADC & IN_IBAT are normally off, are there any powerup delays after setting EN_ADC=1 & EN_IBAT=1 before initiating a one shot ADC conversion?

    Not sure I understand what a "reasonableness check" means. We need to be able to at least crudely measure mAh charging/discharging. I realize this is not a gauge part, but ADC accuracy specs would be greatly appreciated. What's the point of having a 16b ADC if it is inaccurate?

  • 0 in reply to Peter Schmuckal
    TI__Guru**** 166696 points

    HI Peter,

    I am not aware of any delays before the one shot conversion can be taken.  

    Unfortunately, I do not have any accuracy data.  I will forward your request for accuracy data to my management.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 350 points

    Hi Jeff,

    Any updates wrt ADC accuracy information?

  • 0 in reply to Peter Schmuckal
    TI__Guru**** 166696 points

    Hi Peter,

    Unfortunately, it is not going to happen for this device.  Going forward, our new devices with have ADC accuracy spec.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 350 points

    Jeff,

    Well that's disappointing. Do any of the current devices have characterized ADC accuracy specs?

    We have also looked at the BQ25622E & BQ25628E, but they also appear to lack any ADC accuracy specs.

    Can we get a roadmap of your new devices?

  • 0 in reply to Peter Schmuckal
    TI__Guru**** 166696 points

    HI Peter,

    The recently released BQ25638 has the spec below:

    Currently plans are to add similar specs for ADC voltage measurements on future devices.  I am unclear on how this spec translates to the current measurements.  Switching noise and temperature introduces errors for which we cannot account on the tester. 

    Regards,

    Jeff