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TPS65218D0: PMIC Enable Issue. Continously tries to turn out but disables immediately.

Tony Spagnolia1
Prodigy 190 points
Part Number: TPS65218D0

Hi there,

The TPS65218D0 we are using on our design continuously tries to turn on but immediately disables. We want to set it so it turns on as soon as power is applied and not rely on the push button input. What have we wired wrong? See attached for a snapshot of the schematic.

  • 0
    TI__Genius 10885 points

    Hi Tony,

    This schematic indicates that the switch nodes of the DCDC1, DCDC2, and DCDC3 are incorrectly connected directly to the output capacitors, bypassing the inductors.

    The inductors should instead be placed directly between L1, L2, and L3 and the output capacitors, with FB1, FB2, and FB3 directly connect to the output capacitors.

    To boot automatically and remain active whenever power is applied, PWR_EN may be pulled up to +5V instead of the 1.8V rail.

    Best Regards,

    Rick S.

  • 0 in reply to Richard Solarski
    Prodigy 20 points

    The inductors being in the wrong place should not prevent the unit from staying powered up. And with the PWR_EN pulled to +5V the PMIC still does not stay on. 

  • 0 in reply to Nick Nagrodsky
    TI__Genius 10885 points

    Hi Nick,

    Please monitor FB1, FB2, FB3, and PGOOD with an oscilloscope during the restart behavior.

    The datasheet indicates that power good faults will cause the device to reset. The pgood thresholds are observed using the FB nodes of each regulator.

    Best Regards,

    Rick S.

  • 0 in reply to Nick Nagrodsky
    TI__Mastermind 30280 points

    Nick,

    Is R97 installed? It does not say "DNP" (but other resistors, like R16, specifically say "DNP").

    If R97 is installed, then you should remove it.

  • 0 in reply to Richard Solarski
    TI__Mastermind 30280 points

    Nick,

    I also agree with Rick that the incorrect placement of inductors L1, Le, and L3 will have very negative effects on the performance of the system. This wiring will not work and will result in frequent resets. Every time the high-side FET is closed, the output voltage will ramp up to the input supply very quickly (the only thing slowing it down is the output capacitor), resulting in an overvoltage (VOVP) fault. Then the low-side FET is closed and the output voltage will sharply drop to 0V, resulting in an undervoltage (VPG) fault. This will never result in a stable output within regulation.

  • 0 in reply to Brian Berner
    Prodigy 20 points

    Yes, we rewired the inductors to put them in the correct spot and the DC-DC's came up :) Thanks for the assistance. We did not fully understand the internals of this component when we did the design.