We have a deisgn using the i.MX28 MCU with both 5V and battery power supply. It closely follows the iMX28 evk design.
The board is running a custom uBoot+Linux solution based on Yocto with a kernel module to control charging and 5V<->battery transitions.
We found a similar problem to the one that @djernaes (Kim) found in
https://community.nxp.com/t5/i-MX-Processors/imx28-charging-stops/m-p/842609
If the external 5v is removed, the battery takes over. If the external 5v is restored the 4p2 and DCDC takes over BUT the battery charger does not recover.
We found that we have to cycle the BM_POWER_5VCTRL_PWD_CHARGE_4P2 in HW_POWER_5VCTRL to get it started again. No register values seem tom be wrong and no other action (other than a complete power cycle) seems to recover the charger.
At the point in the code where we cycle the 4p2, we turn the DCDC off using BM_POWER_5VCTRL_ENABLE_DCDC so that the linear regulators take over (we need to run off linear regulators at this point in case the battery is too flat).
On some units the change over to the linear regulators fails with a drop in level in the VDDA and VDDD to the point where the CPU can't keep going.
Has anyone else had issues with the changeover from DCDC to linear regulators?
(In some cases we can avoid the dip in VDDD by setting VDDA to 2.0v (instead of 1.8v) just for the brief time that is needed to cycle the 4p2)
