[sdiy] PSU rise-time and uP reset

[Trevor Page]

Hi list,

This is going to be a bit of a 'How long is a piece of string' type
question, but here goes.

Say we have a microcontroller that contains an internal POR (Power-on
Reset) circuit. The datasheet for this device specifies that the +Vdd
rise rate, to ensure good POR operation, should be at minimum 0.05 V/ms.
If this cannot be guaranteed, then the user is advised to use an
external reset circuit. 

I know a reset circuit is only a negligable amount of components, yet I
am still curious as to whether I could get away with using the internal
reset circuit or not. The design in question is a MIDI to CV converter
(yawn!) that will be used by more people than myself and I have no idea
what sort of power supplies are going to be in use. 

Would it be unsafe to make the assumption that the rise time of the 5V
from my on-board 5V regulator, which takes its power from the modular
+12/+15V PSU, is going to take longer than, say, 100ms to fully rise?

This is a really stupid question, isn't it? I reckon I should just stick
to using a slow RC reset.. 

Regards,
Trevor.


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