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micro power voltage monitor - active high latching output?

Graham North
Prodigy 230 points
Other Parts Discussed in Thread: TPS3837, SN74LVC1G80, TPS3806

Hi,

I'm trying to build a high side switch cut off for a Li-Ion battery pack using a voltage monitor IC and a PFET. I've proved that the theory works with a TPS3837, but obviously as the battery is disconnected from the load the voltage comes back up and the FET is enabled again.

Is there a similar part that latches? I can't find one.

I'd actually be interested in adjustable voltage set level if it existed also.

Thanks

G

  • 0
    TI__Guru 55940 points

    Hi G,

    Have you considered using a follow on flipflop such as SN74LVC1G80 to provide the latch?  

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 230 points

    I'm not really sure how that will help me, let me explain what I am trying to do further.

    I have a 1 cell Li-Ion battery that I want to remove from the main circuit at a certain voltage level. So the voltage monitoring circuit and latch etc need to be super low power, as they will run from the battery still when it is disconnected - and the whole point of disconnecting it is to stop it over discharging! :-)

    When the device is plugged back into USB the on board micro needs a way to reset the voltage monitoring circuit to re-connect the battery to allow it to be charged again by the bq2403.

    Does that help?

    Thanks,

    Graham

  • 0 in reply to Graham North
    TI__Guru 55940 points

    Hi Graham,

    I'm sorry, I must still not be picturing your application.  Could you share a block diagram and a timing diagram of how you want the supervisor to operate?

    To answer your original question, I am not aware of SVS devices with latching output.  Likely we will need to investigate a combination of an SVS and something like an inexpensive flip flop in order to provide the latch.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 230 points

    Hi,

    OK, here goes, I'll try and explain it better :-)

    So the battery is connected to the Charger and PSU circuitry by the PFET.

    The PFET conducts while the battery monitoring circuit measures the battery voltage as healthy - the voltage level is still to be determined, but maybe around 2.7V?

    Once the monitor circuit has determined the voltage level is below the threshold, it should turn off the PFET and latch it off, it shouldn't turn the PFET back on as the voltage comes back up because it has no load any more.

    The microcontroller should be the only thing able to reset the battery monitoring circuit to turn the PFET back on.

    Does that make sense?

    Thanks,

    Graham

  • 0 in reply to Graham North
    TI__Guru 55940 points

    Hi Graham,

    Thank you for the explanation!  Please take a look at TPS3806. This family enables you to select the threshold that you would like /RSTSENSE to go low and a higher threshold where you allow it to go high again.

    Very Respectfully,

    Ryan