Re: Diodes for Li coin cell protection

From: rickman (spamgoeshere4_at_yahoo.com)
Date: 02/23/05 

Date: Wed, 23 Feb 2005 17:36:05 -0500

Guy Macon wrote:
> rickman wrote:
>
>
>>Diodes are the right idea, but primary Li cells have a very low
>>tolerance for reverse current (charging). It seems that reverse
>>current builds up a layer inside that reduces the capacity of the cell.
>
>
> Do you have any numbers for this very low tolerance?

Panasonic CR/BR types are rated by the capacity of the battery; Within
3% for coin-type batteries and within 1% for cylindrical type batteries.

With my conditions, I get

120 mAHr * 0.03 / (24 * 365.25 * 5) = 82 nA

I have found some very small, very low reverse current parts at Central
Semiconductor. They seem to specialize in very compact parts. I can
get dual diodes in SOT563 packages which are less than 2 mm square and
are rated for under 1 nA at 25C. Or I can get dual transistors with
Icbo of 10 nA max at 25C. The advantage of the transistors is that I
don't have to stock a separate part. But may I need to do some tests to
make sure the Icbo does not increase too much at higher temps.

Rick "rickman" Collins

rick.collins@XYarius.com
Ignore the reply address. To email me use the above address with the XY
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Arius - A Signal Processing Solutions Company
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