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BQ78350 Vaux external circuit

Matteo Rigamonti
Expert 1170 points
Other Parts Discussed in Thread: BQ78350

Hello!

I can't find any reference schematic for using the Vaux input pin of the BQ78350. The Technical Reference document, on page 10, seems to say that also the Vaux reading is timed in the same way the Vbat is. So I suppose I have to use the same reading circuit of Vbat, with an enabling p-ch MOS to be driven by the Ven pin.

Is that correct?

Thank you in advance for any answer.

Matteo

  • 0
    TI__Expert 6470 points

    PWR524A_Sch.PDFHi Matteo,

    No, the Vaux input does not use the VEN signal to enable it. Reference schematic is attached.

    Regards,

    Doug

  • 0 in reply to Doug Williams4811
    Expert 1170 points
    Hello Doug,
    and thank you for your answer.
    I would like to read the Vaux input under the VEN timing, in order to activate the voltage divider only when necessary and saving power. So my question was a little different: is it possible to use the same Vbat enabling circuit also for the Vaux input?
    I've read on page 10 of the Technical Reference document:

    <<
    The VEN pin will go high 2 ms prior to the BAT being measured if DA Configuration [ExtAveEN] = 1, and then return low unless DA Configuration [VAUXEN] = 1, which will cause VEN to remain high for a further 2 ms prior to making the VAUX measurement. This results in VEN possibly being high for up to 40 ms per second in NORMAL mode.
    >>

    If I understand well, it means it is possible to use the enabling circuit for Vaux and, if DA Configuration [VAUXEN] = 1, the BQ78350 automatically manage the timed reading.

    Is that correct?

    Thank you very much in advance and best regards

    Matteo
  • 0 in reply to Matteo Rigamonti
    TI__Guru 54715 points

    Yes, you can use VEN to switch the VAUX circuit similar to the one Doug showed.  You need another high side switch like Q15 with divider components for the PACK voltage to VAUX.  The new switch will also need a separate gate divider. The switching transistor Q16 should be able to be shared between the BAT and VAUX switches using blocking diodes to prevent current flow around the switches through the gate dividers. 

  • 0 in reply to WM5295
    Expert 1170 points
    Perfect and clear!
    Thank you very much

    Matteo