AVR (FLASH) unable to reset if supply voltage falls to 1V...

Log in or register to post comments
Go To Last Post
4 posts / 0 new
Author
Message
pieterc
pieterc's picture
Level: Wannabe
Joined: Mon. Mar 5, 2001
Posts: 58 View posts
Location: Cape Town, South Africa
#1
Posted by pieterc: Tue. Aug 29, 2006 - 01:31 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I have a circuit where the AVR's supply voltage is kept at 1V (when switched off) by drawing parasitic power from an external source (+5V to 1k resistor, through protection diode of AVR input pin).

When power is restored (VCC = 5V), the AVR fails to return out of reset. The BOD or external reset has no effect. The issue was solved by using a 10k resistor, which limited the parasitic power voltage to 0.2V.

Has anyone had a similar experience? Is this a known issue with FLASH?

Regards,
Pieter
http://www.piconomic.co.za

Tags:

AVR Microcontrollers, megaAVR and tinyAVR
Top
Bronze Marktheusch
theusch's picture
Level: 10k+ Postman
Joined: Mon. Feb 19, 2001
Posts: 40538 View posts
Location: Wisconsin USA
Posted by theusch: Tue. Aug 29, 2006 - 01:58 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

This can be a tricky situation. First, which AVR model are you using? Those with AVcc need to have both Vcc and AVcc drop below the BOD hysteresis level before a restart will be done. This can be a problem in systems with lightly-loaded analog supplies.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Top
MegaUSBFreak
MegaUSBFreak's picture
Level: Raving Lunatic
Joined: Sat. Aug 21, 2004
Posts: 2223 View posts
Location: germany
Posted by MegaUSBFreak: Wed. Aug 30, 2006 - 08:43 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi,

maybe this is some kind of latch up effect.

I had a similar(?) problem with a simple mosfet. Once powered in reverse the gate was not high ohmic anymore.
(The fet was not dead, but it needed some 100microamperes to the gate to get low impedance. This effect was reproducible.
Driving the FET with >100kOhms failed while driving the gate with <100Ohms worked fine)

The solution to avoid this effect was to place an external schottky diode in parallel with the internal body diode.

Maybe in your application an external schottky diode in parallel to the AVR internal protection diode helps....

Klaus
********************************
Look at: www.megausb.de (German)
********************************

Top
sgomes
sgomes's picture
Level: Resident
Joined: Wed. Feb 19, 2003
Posts: 919 View posts
Posted by sgomes: Wed. Aug 30, 2006 - 01:22 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Yep, Klaus got it. We had a similar problem in one of our products. Same solution. Turns out that if you don't have enought current (which it sounds like you won't) you won't develop the full 0.2V so this will result in an even better situation for your reset!

Go electric!
Happy electric car owner / builder

Top