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TPS543620: Keeping Enable Low

Part Number: TPS543620
Other Parts Discussed in Thread: TPS54824, TPS54620

Hello E2E,

I think I know the answer here, but want to check with the gurus. :)

I have a customer who is driving the EN of the TPS543620 with a PMIC.  The PMIC is powered off of the same 12Vin rail that the TPS543620 is powered off of.  They need the TPS543620 to power up AFTER the PMIC.  However, if we leave EN floating the device turns on.  Unfortunately, the PMIC cannot control its EN drive state when powered off (logic state unknown).  Because a floating EN still turns on the device, the TPS543620 is powering o when 12V is applied, which is before the PMIC tells it to.

Ideally they would like to avoid a layout change and keep EN low until after the PMIC powers up.  Any workarounds here that you can think of?

I'm thinking that a layout change will be necessary here to add in a pull down resistor.

Also, why did we default enable to on?  That seems pretty atypical.



  • Hi Russell,

    Unfortunately there are not any workarounds and the schematic + layout change is needed to add the pull-down resistor.

    The EN pin was done this way to match the functionality of the previous generation of devices (TPS54620 and TPS54824). If we changed the functionality, we might have had issues where other applications were expecting that floating the EN pin enabled the device. The primary reason I can think of why floating the EN pin can be preferred is it can simplify the schematic and minimize external components. However, I believe most schematics I see with these device families usually use some other device to pull EN high so I do see how EN floating disables the device by default may be better.