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BQ33100: REG27 question; Possible datasheet Typo

Ronnie Hughes
Expert 3080 points
Part Number: BQ33100

Is REG27 powered from VCC, VCCPACK, or both?  What is the minimum voltage level required on VCC and/or VCCPACK in order to keep REG27 in regulation?

From this picture. it looks like we have plenty of headroom on VCCPACK (red waveform) and 12.0VB goes to VCC (blue waveform). You can see REG27 starts to fail well above what i'd expect. I do not see a good spec on the LDO inside the device for REG27...I need to understand if it runs from VCCPACK OR VCC or just VCC and what is the minimum voltage to maintain operation.  I do not see a clear spec here (same typo here VCC = VCCPACK ?)....even so it seems to say 3.8V works and my picture shows it failing before that on either rail feeding the chip. 

Also, does shutdown condition also shutoff REG27?

It appears that the Recommended Operating Conditions table in the datasheet has a typo with regard to:

- Vshutdown; should this be VCC or VCCPACK, whichever is higher. 

And in REG27 LDO table, VCC and VCC, should 2nd one be VCCPACK?

  • 0
    TI__Expert 3080 points

    FYI - we took a look at this where we do not activate the discharge load (which is driven from REG27 output to that transistor in the picture). In this case the REG27 voltage stayed up. So it seems to me that this is related to that load enabling. We are going to try some more experiments, not quite sure yet why it's failing but it doesn't seem to be a simple Vin minimum anymore.

    Out schematic is taken from your app note circuit pretty much: