[sdiy] PSU rise-time and uP reset

[Paul Maddox]

Trevor,

> 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 would recomend the use of one if you're not sure.. With the AVRs you can
set a sort of powerup delay, so if it takes your power supply lines a moment
to settle you can set these fuses and the cpu will just wait a moment, very
handy...

> I know a reset circuit is only a negligable amount of components,

err, yes, one TO92 style case, Maxim do one, though I forget what its part
number is.

> 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.

Then you should play it safe and use a POR device.

Paul