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TPS650832 VR3 during forced off

Antony Lin
Genius 13480 points

Hi,

Now customer configure FLT timing to 15sec for forced off timer on PWRBTNIN.  When the timer expires, they found VR3 is turned off as a 2-step curve, but other rails are turned off immediately.  (Please check the scope shot as below.)  Please let us know your comments if this is normal or not?

Thanks!

Antony

  • 0
    TI__Genius 17380 points
    Hi Antony,

    Is this on a customer board or an an EVM? My first thought is that VR3 is disabling properly at that time, but if any other voltage regulators are still on they could be leaking voltage onto this output through other ICs on their board. We can see that the DRVHVR3 is well below Vth, so the voltage does not appear to be coming from the VR3 output. Can they probe other rails and see which rail turns off at the second turn off point?
  • 0 in reply to Kevin LaRosa
    TI__Genius 13480 points

    Hi Kevin,

    This is measured at customer board.  Please check below for a similar waveform plot, DRVHVR3 is around 1.3V before VR3 reaches 0V, is it normal bahavior and normal voltage level?

    Customer also said that they need to press the power button ten(sometime five) more seconds to allow VR3 reaches 0V.  If they release the power button when VR3 is still 1.1V, VR3 would keep at 1.1V until next power the power button is triggered again.  By doing so, VR3 would rises to 3.3V, but their EC would enter a dead loop.

    Meanwhile, they found all other rails dropped to 0V directly.  Besides, VR3 actually discharge to around 0.5V shortly and back to 1.1V.  What is your comment?

    Antony

  • 0 in reply to Antony Lin
    TI__Genius 17380 points
    Hi Antony,

    DRVHVR3 when disabled will be set to SW3 voltage as the driver is referenced to SW3. For example, if driver is ON, it is 5V above SW. If it is OFF, it is equal to SW, that way Vgs of FET can be utilized. In this case, SW3 = VR3 when not switching.

    They need to find where this voltage is coming from, it does not appear to come from VR3 high side FET, but rather another rail. They should scope multiple rails until they find one that turns off at the same time that VR3 drops.