Internal vs external BOR and WDT

[C-H Wu]

Dear friends:

In case of power glitch, my 18F4620 sometimes stucked in RESET and sometimes jumped to wrong locations and of course ... crashed my project

My question is, if I enable internal WDT and BOR, would it be necessary to add external system supervisor like MCP130 (MCU Voltage Supervisor) or TC32M (System Supervisor with Power Supply Monitor and Watchdog) to get more reliability ?

Thanks a lot for your suggestion and comments

C-H Wu

[ckielstra]

I'm not an expert in these things, but my guess is the internal circuits of the PIC are just as good as any external power monitoring devices you can add externally. I just use the internal circuits.

Running a serious project without any of these protective features enabled is asking for troubles.

If your power-up time can spare a few miliseconds I recommend to enable the Power Up Timer (PUT) as well.

[Ttelmah]

Realistically, the internal circuits are fine, if they do what you want. The advantage of external circuits, is that you can sometimes do more, with different voltages, detection at different points in the supply, and more accurate watchdog timings, as 'examples').
Generally, I'd say that the oscillator startup timer is your friend, if you are using a crystal oscillator, where many units can display 'spurious' behaviour as the oscillation starts and stabilises (you don't mention this one). BOR, is essential, unless you are providing some other form of protection (watchdog, or an external 'power fail' based on an incoming rail). Designing good watchdog code, is important if you use this (remember that the watchdog being reset, should depend on the chip actually being in a 'good' running state, just putting lots of resets throughout the code, can partially invalidate the usefulness of this circuit). The WDT on it's own, if properly implemented, can recover from a 'brownout', but the two together are a 'safer' solution.

Best Wishes

[C-H Wu]

I do have PUT, however, I never realized that BOR can be so important

Thanks a lot for your comments.

Best regards

C-H Wu