A few years ago we designed a system based on the IMX6 processor. Voltages for this design are controlled by a PMIC (PF0100NPEP up to now). The PMIC configuration is done through an I²C interface (thanks to a programmed microcontroller). This system was used in the past years.
We are now manufacturing new cards with the new PMIC version (PF0100NPAEP), the previous one being obsolete. These new PCBs work nicely but for an issue during booting. When booting we observe two different behaviors:
- If the card was not recently (recently is a maximum of around 4 seconds) plugged in, the card will not boot.
- If the card was plugged recently, the card will boot.
By observing different signals on the card during power-up we deduced that PMIC is in cause. More precisely signal VSNVS (and associated PWRON) do not behave correctly.
The associated circuitry (or the rest of the PCB) should not be in cause since we were able to obtain good results by changing the NPAEP back to NPEP on one of the new cards.
The program used in the PIC to configure PMIC (by I²C) was not modified during the tests.
Recordings of the measured VSNVS signal are in attachment in three different cases:
- When PCB is not booting (with NPAEP version): signal takes the wanted value (3V) for a short time and then goes back to 1V.
- When PCB is booting (with NPAEP version): we see an unwanted step at around 2.6V but the final value is what is expected.
- When (new) PCB is booting with an old NPEP version we still had in stock. We were able to replace NPAEP with NPEP version. This card behaves as expected.
We were not able when going through the PMIC datasheet and errata to find what change which occurred between NPEP and NPAEP version could cause this type of behavior.
Would you have any idea of what could cause this behavior ? Any idea on what we could do to solve this ?