SNAPHAT battery/xtal problem

Nov 15, 2005 2 Replies
G

We have an 'old' product that uses the STMicroelectronics M48T86 RTC, with a "SNAPHAT" battery/xtal backpack that plugs into (4) sockets on the chip itself. The idea was that you could plug the battery in after going through solder.



Until recently, this has worked fine. Now, we're seeing a significant number of units where the oscillator (32.768 Khz) stops when 5v power is removed from the chip. Battery voltage appears to be OK. The oscillator runs when the chip is powered.



If anyone has any experience with this, I'd appreciate hearing it. Brilliant insight also welcome.



TIA, George


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P

"George"

** The battery voltage may seem OK - but what about the battery's internal resistance.

Old cells go high "ESR" before the voltage drops.

Try paralleling the battery with a 47uF electro.

........... Phil

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G

For google-completeness: once I got to actually look at one of the offending units, I found that the 48T86s' internal connections between Vss and batt V- were open. Probably, reflow needs to be tuned.

G
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