I'm studing the interactions between the i.MX6 processor and the PMIC MMPF0100 using the Sabre SD board Rev C2.
I need to understand how the power is managed before implementing our own project using these two components.
Actually when the Sabre board is powered for the first time using switch SW3, the PMIC applies all powers to i.MX6 processor and the system performs the boot procedure.
I think that this occurs for the presence of 10K resistor R31 that brings to high level (3.0V from VSNVS_3V0 power) the PMIC PWRON input.
I don't want this automatic power on feature, I want that the system boots up only after the user presses the PWR button (swithc SW1).
Then I removed resistor R31 and in effect the system don't boot anymore when power is applied through SW3.
Unfortunately the system don't boot anymore pressing SW1 switch.
I measured some voltages around the board:
SYS_4V2 = 4.6V
VSNSV_3V0 = 3.0V
MX6_ONOFF = 3.0V with SW1 not pressed, 0V with SW1 pressed.
PWRON = 2.04V with SW1 not pressed, 1.58V with SW1 pressed.
The problem is on the PWRON signal voltage driven by the PMIC_ON_REQ by the R30 1K resistor:
Why is the PMIC_ON_REQ to 2.04V if the processor is in OFF state?
Why don't the PMIC_ON_REQ go to 3.0V when the SW1 is pressed and the processor is turned ON?
Thank you to the one that can explain to me this behaviour.