Why do we use external supply monitoring IC (Power on Reset IC) for microcontroller?

[myatham]

Hello,
I have seen in few designs, even the microcontroller has internal power on reset, external power on reset IC are used? Do the internal feature is not reliable?
When we use external power on reset?

 

[FoxyRick]

It might be due to:

1. There are other devices to reset besides the MCU
2. The power supply start up might be (possibly) slow, so a configurable external POR chip makes sure of things; the MCU's POR might not handle a slow power ramp-up.
3. Other, dependent on the MCU in question.

P.s. should this post be in the Microcontroller forum, not analog design?

 

[keith1200rs]

A lot of microcontrollers now have the necessary reset and brownout detection circuitry so it shouldn't be necessary to use an external chip.

Keith