Power Good Signal

[Bluestreak66]

How is a power good signal implemented in a circuit design? Can it be tied to a reset pin on a micro with a pull-up resistor? This would hold the micro in reset until power is stable then let the micro power up, assuming active low. Is this good practice? How is it usually done?

[Bluestreak66]

Ok so this is commonly done I found my answer in another post on the forum. If I have multiple regulators can I tie all the power good signals together and have a single reset line on the board to start everything at the same time once power is good? Would there be an issue with this? I could cascade the regulator also so one turns on the other and so on and the final lifts the reset to turn everything on.

[digsys]

I rarely bother with power good these days. Many micros have their own voltage monitor / inhibit / reset circuits built in with flags set from
a POR telling you what caused the Reset. Plus I usually always monitor V_in and any other DC Supply so the micro can inform / store
problems with DC levels. No good getting stuck in a endless PG / POR loop that you can never control or know anything about.
Whatever is happening out there !! I want my micro to make the decisions.

[Bluestreak66]

I have 16 asics I want to reset together and I think this would be a good way to do it. I probably will not tie the micro reset in with them. Thats a good point about having an endless loop.

[madires]

Ok so this is commonly done I found my answer in another post on the forum. If I have multiple regulators can I tie all the power good signals together and have a single reset line on the board to start everything at the same time once power is good? Would there be an issue with this? I could cascade the regulator also so one turns on the other and so on and the final lifts the reset to turn everything on.

You could use a common pulled up signal line. Any unhappy regulator would pull down the line and you'll know :-) There are also some power/battery management ICs which monitor several power sources.

[digsys]

  I have 16 asics I want to reset together and I think this would be a good way to do it. 

Sure, but IF the micro doesn't start up, or finds other fatal conditions during its POR routine, you'd want it to override any auto-start
or be able to control a new start ? I'd always let the micro decide that stuff. Maybe feed the PG to the micro as an Input?

  I probably will not tie the micro reset in with them. 

Oh yeah, no way :-)

[Bluestreak66]

The only reason I was considering this is the voltage regulator I'm using has a power good signal coming out of it. The reference design uses a rc reset for each Asic. I figured I'd just use the power good signal as the POR. That would knock out 32 components from the original design without adding additional components. Yea Ideally It would be great to have the micro control the reset, but all pins are being used and I plan on using the firmware from the original design without much modification. So I don't want to go and reinvent the entire wheel here. The original design seems to have a lot of redundancy and I'm trying to thin it down and make it more efficient. If I were to use the micro to control the reset how would I do that? Tie one pin to the resets with a pull down resistor then use the pin as a pull up to lift the reset? I may do this in rev2 once I'm comfortable with the changes I've already made. Thanks for the input.

[digsys]

... I plan on using the firmware from the original design without much modification. So I don't want to go and reinvent the entire wheel here.

Fair enough. I didn't know your situation.

If I were to use the micro to control the reset how would I do that? Tie one pin to the resets with a pull down resistor then use the pin as a pull up to lift the reset? 

I always have RST HELD-ON (on peripheral devices) in the non-startup condition. If the micro fails to Initialize, everyone stays DEAD :-)
Most micros IO start up in high-impedance, so all you need to do is work out the active high/low sequence.

I may do this in rev2 once I'm comfortable with the changes I've already made. Thanks for the input. 

Welcome. Hope it helps