We built a system based on the AM335X_EVM_15X15BASEBOARD design. Especially we supply VDDS_RTC using a regulator from VBAT, similar to the EVM. The PMIC implemented is the TPS65910. The only battery in the system is a CR2032, supplying backup power to the RTC embedded in TPS65910. As in the EVM schematics there is no RTC backup power to Am335x, when the external power is removed.
Problem is twofold:
1) When external power is applied, the system starts immediately. There is no need to push the power button.
2) Much worse: It is not possible to power off the system. Instead it immediately restarts.
A long press of power button to shut down the PMIC power supply is partially successful. After roughly 10 seconds pressing the button the power supply to Am335x shuts down. But when the button is released, the system starts again.
It is also possible to shut down the PMIC by use of the DEV_OFF bit in TPS65910. But also here the system immediately restarts.
As we could see the problem seems somehow related to the signal PMIC_POWER_EN (Ball C6 on ZCZ package). This connects to PWRHOLD (pin 1 on TPS65910). Even in off state after 10s power button still pressed, this signal stays high (1.8V). Seems this high level causes TPS65910 to supply power again, once the button is released.
If we disconnect this signal from TPS65910, the system can not start. Not even after pushing power button.
Is that a known issue with EVM Design, Am335x or TPS65910? How to solve that problem? In particular, is there any software solution to switch off the system so it will stay off?
Thanks for any help and information.
