I have had on two occasions, one on a volume production situation, had a
processor which would not start if supply rise time was too slow, even
though the data sheet said it should. Once Vdd had passed above a certain
level and non-starting had happened (it was an "even" which could be
observed) the processor would not start until the Vdd had been cycled to a
very low level - probably under about 0.2V.  The system was powered by
human action (exercise bike) so slow start of the actual raw supply voltage
was not preventable.

The only solution that worked for me was to make a supply starter which
isolated  the processor Vdd and then applied power rapidly when adequate
voltage was available.  I think the sartup circuitry used 2 or maybe 3
jellybean transistors and a few passives and diodes. Probably cheaper in
production than a "power good" capable regulator.


             Russell
--=20
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