in an application we use the iMX537 MCU which is powerd by a PMIC MC34708. Until now we produced a 1000 boards without any problem.
With the last batch of boards (250 pieces) we have a problem on 10 boards with the coin cell back up.
There is a 3V coin cell connected to the PMIC.
When the power is applied (BP = 3.8V) VSRTC = 1.3V --> OK
When the power is removed and the cion cell has to take over, VSRTC drops down to 0V.
We have replaced the PMIC on 3 boards and the problem was gone.
That looks like the PMIC is bad, has anybody experience the same problem ?
Could there not be an other reason for that behavior ?