TPS65720: PB_IN Input

Mason,

On most PMICs (TPS65217, TPS65218D0, TPS65070) it is not a good idea to pull PB_IN (push-button) input down to GND permanently.

Typically, if the PB_IN pin is held low for longer than 8 seconds, it will trigger a system reset. I do not see this feature in the TPS65720 datasheet, but I will need to confirm that it is OK to pull down PB_IN. The datasheet recommends a pull-up resistor and a physical push-button, so a pull-down resistor goes against the recommendation.

Mason,

I tested on the TPS65720EVM-515 and the results are as follows:

-The PB_IN input, HOLD_DCDC1, and HOLD_LDO1 are meaningless when power is applied at VIN. If you have line power from an AC-DC adapter, then the PMIC is always 100% on.
-When power is only applied at BAT, the PMIC needs PB_IN to go low in order to turn on.
*If PB_IN is held low before BAT is applied, the system powers on as expected
*If PB_IN is always held low, the systems operates correctly. There is no reset timer on this device.

Therefore, your system will work correctly is PB_IN does not have a pull-up resistor and instead has a pull-down resistor on the PB_IN pin.

The only downside is that when you are running off of battery power the system is effectively always-on and the battery will not last as long.

If you use an MCU signal to set the PB_IN pin high, keep in mind that you also need to set HOLD_DCDC1 or HOLD_LDO1 high before setting PB_IN high. If PB_IN toggles from low to high while HOLD_DCDC1 and HOLD_LDO1 are both low, then DCDC1 and LDO1 will shut off. The end result of doing this would be a reset, but it would be because of the logic of the MCU (not because of the PB_IN pin itself).

Thank you for your kind support. It was very helpful to me.