[FAQ] TPS659037: Should I use PWERHOLD or PWRON to turn on the PMIC?

In general it is recommend to use POWERHOLD (GPIO_7) to enable and disable the PMIC. POWERHOLD does not require any software to keep the PMIC on since POWERHOLD is its own power acknowledge. POWERHOLD also has no debounce time (PWRON has 15ms debounce), so POWERHOLD provides a faster power-up sequence. Regarding power-down, it is a processor requirement to meet the power down sequence even if the supply is unexpectedly removed. For this reason it is recommended to connect a powergood signal from a pre-regulator to POWERHOLD, or using a supervisor on the VCC supply and connecting its reset output to POWERHOLD. A second option is to tie POWERHOLD high permanently (eg. to LDOVRTC_OUT), and connect a powergood or supervisor reset to RESET_IN. Either of these configurations allow the system to turn on when power is supplied, and will disable the PMIC before power is lost to ensure the processor's power-down sequence is still met.

If it is desired to use a push-button to turn on the PMIC, then PWRON could be used. PWRON should be connected to a switch which shorts to GND when pressed. Once powered up using PWRON, the PMIC will remain on for 8 seconds, during which time the DEV_ON bit must be set by software in order to keep the PMIC on. Then to turn off the PMIC, software must set DEV_ON to 0. PWRON can not be tied low permanently, as this would trigger the "LONG_PRESS_KEY" function, hence the PMIC would power down after 6 to 12 seconds. You must take care to disable the PMIC before power is removed, in case there is a sudden loss of supply power. The processor should receive some interrupt from a powergood signal or supervisor indicating that the system supply is dropping, and should disable the PMIC by setting DEV_ON to 0 so the PMIC can complete the power-down sequence. RESET_IN could be used as a hardware option to disable the PMIC, but setting RESET_IN high will enable the PMIC again, so it will not be gated by a push button after RESET_IN is set low.

Note that if RESET_OUT is toggled during warm reset (BOOT1=1 in TPS6590376 and TPS6590377), then POWERHOLD must be used. If POWERHOLD is set to 0V while RESET_OUT is toggled during warm reset, the PMIC will instead shut off. BOOT1=1 can be used as a workaround to AM572x silicon errata (Issue i862).