RTC Battery Drain

Added by Thomas Catalino almost 10 years ago

(posted on behalf of a customer)

A quick question for you, or perhaps someone else on your team, regarding
the RTC on the L138 modules and the profibus development kit battery:

We have noticed that the RTC batteries have been running low quickly. For
example, we installed two batteries last night that were reading around 3.5
V. We checked them this morning and they are now around 2.7 V.

We might have bad/old batteries. However, all of our profibus development
boards have a low RTC battery on them, so we are curious if there is some
other root cause.

I noticed today that the linux driver we were using was clearing a "split
power supply" bit in the RTC control register on boot, which might account
for an increase in the leakage current and thus low battery life (see page
24 of, the SPLITPOWER bit of
the RTC control reg). I hope that will fix the issue -- time will tell.

So, I am simply curious -- have you seen the RTC battery running low before?
Any recommendations? Perhaps even a part number/supplier of "known good"
batteries? Any advice or suggestions would be greatly appreciated!

Replies (2)

RE: RTC Battery Drain - Added by Michael Williamson almost 10 years ago


Wanted to follow up on this. We have seen RTC battery drainage, but at the time we looked at it we were using Revision A silicon OMAP-L138 parts, which had some errata about power leakage that was fixed in the Revision B (standard populated parts). So we had set aside the testing. I have also seen the issue with the SPLITPOWER bit you mentioned. Have you tried this since your post?

We'll be looking at this again here, shortly.


RE: RTC Battery Drain - Added by Michael Williamson over 9 years ago


There has been an Errata published for the MityDSP-L138 SOMs that includes a higher than expected RTC battery current consumption.

We have implemented a fix for the MityDSP-L138 module family and are currently testing it at Critical Link. The design modification should reduce the current consumption to approximately 10 micro-amps while the unit is unpowered (i.e., 3.3 VIN is disconnected). This fix, following test, will be moving into our next production cycle (the Errata and PCN information will be published once the design has been released from engineering).


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