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LM73606: Power good output valid

Patrick Ruf
Genius 5005 points
Part Number: LM73606
Other Parts Discussed in Thread: TPS659037

Hi,

In the datasheet of the LM73606 it is written that PGOOD output is low if EN is low and VIN>2V (VPGOOD_VALID, typical 1.3V). If we use BIAS Pin to supply the LM73606, is still the VIN level the criteria to when the PGOOD signal is valid? Or is it: (VIN>2V OR VBIAS>2V)? From the functional block diagram this is hard to tell.

This information is important for us as we need to decide wether we can use PGOOD signal to start/stop TPS659037 PMIC or we need an additional supervisor.

Best regards,
Patrick

  • 0
    TI__Expert 4100 points
    Hello,
    I'm checking with design engineer on your question and will get back to you as soon as i have more details.
    In the meantime can you share what type of sequence are you trying to achieve?
    The logic is such that if your PGOOD is tied to Vout, it will stay low when EN=low regardless of Vin value.
    Regards
    Brani
  • 0 in reply to Brani Dubocanin
    Genius 5005 points

    Hi Brani,

    Attached is a drawing what we want to do. Please note that the +5V is buffered with about 600uF to ensure that the TPS6590379 can do a proper power down sequence. So VRTC will stay at a certain level and therefore the PGOOD signal can go up again when LM73606 is not able to control it. We want to make shure that the TPS6590379 will not be able to do a power-up cycle again while the +5V is depleting.

    Best regards,
    Patrick

  • 0 in reply to Patrick Ruf
    TI__Expert 4100 points

    Hi Patrick,

    Thank you for additional details.

    Here is answer i got from design engineer fro this device

    "

    Whether PGOOD is valid depends on VIN > 2V only.  It doesn’t depend on whether there is a VBIAS voltage or not.

    The reason is that VBIAS is not active until VIN is high enough to turn on the LDO and allow all the control logic to run from VBIAS.  So during startup, we will only have VIN as an input.

    The VIN signal will pull up the gate of an NMOS that keeps PGOOD low (which is the valid state) during startup.  The reason VIN needs to be higher than 2V is because the VT threshold of the NMOS is ~1.5V, so we need at least that voltage to keep the NMOS on.

    "

    I hope this helps.

    Best regards

    Brani