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TPS546A24A: Power Down Voltage too Slow

Phillip Lam1
Prodigy 90 points
Part Number: TPS546A24A
Other Parts Discussed in Thread: TPS546D24A

I have about 800uF of output capacitance. VOUT is 1.2V

My VR is configure to power on/off based on the operation register.

When I power down it takes about a minute or so to go below 100mV. Is there a register or setting that can pull this voltage down faster?

Also, as a workaround, I tried setting the voltage to 0V, but it will only go as low as 500mV. What could be the reason why my voltage won't go lower?

  • +1
    TI__Mastermind 48180 points

     

    My deepest apologies for the delay in responding to your question.  Your question was directed to the wrong applications engineer here at TI and I did not see it until now.

    1) Is there a register or setting that can pull this voltage down faster?

    Yes.  The OPERATION command bit 6 is "Soft Off" and controls how the TPS546D24A discharges the output voltage during shutdown by the OPERATION command.  If you set OPERATION to 44h instead of 00h, the output voltage will be discharged according to the TOFF_DELAY and TOFF_FALL settings.  TOFF_FALL defaults to 3ms but can be adjusted from 0.5ms to 31.25ms depending on the falling slew rate you need for your application.

    2) What could be the reason why my voltage wont go lower than 500mV?

    The PMBus command VOUT_MIN sets a minimum target regulation voltage for the output voltage.  When you set VOUT_COMMAND to a value lower than VOUT_MIN, the voltage drops to the VOUT_MIN value.  You could set VOUT_MIN = 0.1V and then set VOUT_COMMAND = 0.1V and the output voltage will drop to 0.1V.