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Can't reliably start 4P2 regulator for a 5V only setup (AN4199).

Question asked by Ryan Bryngelson on Nov 18, 2013

I have an i.MX283 design with which I'm facing a problem reliably starting the 4.2V regulator on a new unit.  My hardware follows figure 9 of AN4199 with the optional RTC backup precisely.  I've modified mainline u-boot (2013.04) to configure the i.MX283 per the 5V only instructions outlined in the application note.  I have a 60mF super capacitor backing up the on chip RTC when power is removed.  I use Freescale's MfgTool to program brand new boards.  If I charge the super capacitor externally before powering up the board everything works well, however, if the super capacitor is completely drained (as it is on a brand new board) the 4.2V regulator will not start and the system will continually reboot preventing the MfgTool from loading the programming application.  Attached is my mainline u-boot patch for 5V only operation.

Is anyone successfully using AN4199 in the 5V only setup with a super capacitor backing up the RTC?  This product is actively being built and shipped, too much time is being spent charging super capacitors by the production team.  Any help would be greatly appreciated.

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