How to brownout op amp

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Henry Parr Contact options for registered users 's Avatar (by Gravatar) posted on
February 20, 2005, 12:36 pm
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I am designing an Atmel-based circuit with an associated single supply
op amp. I do not want the op amp Iq to deplete batteries any further
than down to about 1V after the programmed micro brownout.

Note that the batteries are not to be manually switched off.

What is the simplest way of doing this?

Thank you,

Henry

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Markus Mandl Contact options for registered users 's Avatar (by Gravatar) posted on
February 20, 2005, 3:49 pm
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Re: How to brownout op amp
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Hallo Henry,

you could use an OpAmp with shutdown - like TLV2375 from TI. Another possibility
is to cut off power from your analog circuitry with a small FET like IRLML6302.

Regards
Markus

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Luhan Monat Contact options for registered users 's Avatar (by Gravatar) posted on
February 20, 2005, 8:53 pm
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Re: How to brownout op amp
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Hi,

If its any help here, what I do with PIC's (25 ma for each output) is
use them for a power feed for op-amps, eeproms, and other such.  No
muss, no fuss, just shut down anything drawing less than 25 ma. on their
VCC.  Also, float or drive low any data lines feeding them.

As an example...

http://members.cox.net/berniekm/toycar1.gif

Here, RB5 is used to power an LM324 and associated circuit.

--
Luhan Monat (luhanis 'at' yahoo 'dot' com)
"The future is not what it used to be..."
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Spehro Pefhany Contact options for registered users 's Avatar (by Gravatar) posted on
February 20, 2005, 9:26 pm
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Re: How to brownout op amp

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If there are external inputs to the op-amp (suppose the op-amp is a
CMOS type forming a 1:1 buffer on an input to an ADC, for example) you
might want to make sure the input current is limited and/or tristate
the output powering the op-amp rather than driving it low. Otherwise
you could have a large current flowing from the input, through a
protection diode, to the microcontroller output, to ground.


Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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Steve at fivetrees Contact options for registered users 's Avatar (by Gravatar) posted on
February 21, 2005, 4:43 am
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Re: How to brownout op amp
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Heh - the venerable LM324. You're as much of a dinosaur as I am ;). I
*still* specify these in certain cases; it's almost embarrassing...

Steve
http://www.fivetrees.com



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Joerg Contact options for registered users 's Avatar (by Gravatar) posted on
February 21, 2005, 5:44 pm
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Re: How to brownout op amp
Hello Steve,

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So do I. It's not embarrassing but just plain common sense. After all,
where can you get a comparable quad opamp where each amp costs less than
a nickel?

Then, look at stuff that's even older. I can't count how many times I
designed in a 2N2907 or its SMT sibling and there is no end in sight.

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Hah, we've got six trees here on the lot....

Regards, Joerg

http://www.analogconsultants.com

Nicholas O. Lindan Contact options for registered users 's Avatar (by Gravatar) posted on
February 21, 2005, 6:25 pm
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Re: How to brownout op amp
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The LM324 was the most frequent mention in the recent "Name your
favorite analog IC's" thread in s.e.d.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer:  Electronics; Informatics; Photonics.


Spehro Pefhany Contact options for registered users 's Avatar (by Gravatar) posted on
February 21, 2005, 9:14 pm
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Re: How to brownout op amp
On Mon, 21 Feb 2005 18:25:19 GMT, the renowned "Nicholas O. Lindan"

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Four amplifiers for less than a dime. What's not to like?


Best regards,
Spehro Pefhany
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