Searching \ for '[PIC:] Antibrownout circuit for pin limited proces' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/microchip/devices.htm?key=pic
Search entire site for: 'Antibrownout circuit for pin limited proces'.

Exact match. Not showing close matches.
PICList Thread
'[PIC:] Antibrownout circuit for pin limited proces'
2004\07\16@092443 by Russell McMahon

face
flavicon
face
SUMMARY    Anyone have thoughts on brownout protection for low pin count
processors where reset line is not available?


I note that several of the reduced pin count processors have onboard Reset
BUT do not have anti-brownout circuitry. I am surprised at this (stupid?)
omission in a modern processor, especially so when the reset pin will
usually not be available due to the need to utilise every available pin as
I/O

Both Attiny11 (6 I/O) and the PIC10Fxxx (4 I/O) suffer from this defect.
If one does not feel lead to use prayer as the primary means of brownout
protection then a hardware solution is needed.

One approach is to use the reset pin (lose 1 I/O) and use an external
brownout control chip/cct. IC versions probably exceed the cost of the
ATtiny11.

With no reset pin one can drop the whole Vdd when brownout is detected
externally to trigger POR. Running either IC from the output of an idle-high
/ active low reset generator IC would work.

A simple 1 transistor cct may suffice.
Word art should do.
PNP
emitter to Vcc
Collector to processor Vdd
resistor r1 base to Vcc
resistor R2 base to Gnd.
Cap C1 electro base to Vcc.

Base is biased to slightly on by r1/R2.
Negative spikes on Vcc drop Vcc while base is held by C1.
Transistor turns off.

A more complex form may be needed for stretching time off.

Thoughts on the whole subject?


       RM

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

2004\07\16@112205 by Matt Pobursky

flavicon
face
On Sat, 17 Jul 2004 01:01:37 +1200, Russell McMahon wrote:
> SUMMARY    Anyone have thoughts on brownout protection for low pin
> count
> processors where reset line is not available?

One solution I've used is to drive (switch) the VDD line of the PIC
with the output of your external brownout circuit if ultimate
reliability is required. Make sure all your I/O lines default to the
state you want when powered down, possibly gate any external drive
circuitry with the "power good" signal.

You know the real problem with internal brownout circuits (and the
reason I hardly ever use them any more) is that they are rarely level
programmable which means you have to run the MCU at whatever voltage
the designers set the brownout level at. Most brownout circuits also
have not been nearly as low powered as external circuits and usually
the accuracy is much poorer than external circuits.

This is one area I've hit up Microchip (and others) for improvement on
their MCUs.

Matt Pobursky
Maximum Performance Systems

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

2004\07\16@162550 by Robert Monsen

picon face
part 1 1855 bytes content-type:text/plain; (decoded 7bit)


----- Original Message -----
From: "Russell McMahon" <spam_OUTapptechTakeThisOuTspamPARADISE.NET.NZ>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Friday, July 16, 2004 6:01 AM
Subject: [PIC:] Antibrownout circuit for pin limited processors.


{Quote hidden}

idle-high
> / active low reset generator IC would work.
>
[brownout scheme deleted]

One simple way to do this is with an adjustable shunt regulator like a
TL431. No power to Rpic unless Vcc > 2.5*(1+R1/R2)

For lower voltages, the LMV431 goes down to 1.24V, so the Vbo will be

 Vbo = 1.24*(1+R1/R2)

This part may be more appropriate, since you can use it to specify any
voltage in the PIC's voltage range.

Regards,
Bob Monsen

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics




part 2 3161 bytes content-type:image/gif; (decode)

More... (looser matching)
- Last day of these posts
- In 2004 , 2005 only
- Today
- New search...