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MPC5746R slow startup with internal core reg

Question asked by James Murray on Jan 26, 2018

When using the MPC57XXXMB evaluation board and MPC5746R-252DS processor board to evaluate the MPC5746R, the default jumper configuration is to use the eval board's 1.25V switching regulator.


There are jumpers to use the CPU's internal regulator. The latter seems like a more typical production configuration, so I swapped the jumpers to test it.


However.. now I'm getting a random delay before the processor starts? Is there something I'm missing?


I  checked the voltages between TP16 and TP18 on the daughter card:

Using 1.25SR I get 1.232V and the processor starts immediately.

Using core regulator I get 1.227V then a delay of 0.5s to 3.5s before it changes to 1.263V and the processor starts.


The Reference Manual mentions DCF records, but as the core hasn't booted, I'm presuming that these don't have any impact?