I have been troubleshooting a circuit involving a Maxim DS1306 real-time clock (RTC) with battery back-up. I connected Vcc of the RTC to the same 3.3 V supply as required by the micro that talks to it. The battery is a Panasonic BR2330 (allegedly a 3 V part): -
The RTCs appeared to be failing in droves, in that I could program them once, but after a single power cycle they refused to respond to the micro any more. Replacing the chip always worked, but only for another power cycle.
After barking up a lot of wrong trees, I found postings on other forums indicating that the DS1306 switches from normal mode to battery-backup when Vcc drops below Vbat, but it doesn't switch back to normal until Vcc rises above VBat + 0.2 V.
The Maxim data sheet: -
says that a device in battery mode cannot be written (page
9, last sentence of paragraph under "POWER CONTROL"). On-line user comments indicate that it cannot be read in this mode either. At this point I realized that if the second statement is true, a DS1306 in battery mode cannot be distinguished from a dead chip.I measured the battery voltage and found the 3 V battery supplied 3.22 V, and my 3.3 V supply is unlikely to rise
0.2 V above this--ever. I pulled 7 more boards off the shelf to compare battery voltages:#1: 2.9995 V #5: 2.9887 V #2: 3.1975 V #6: 2.9919 V #3: 3.0579 V #7: 2.9919 V #4: 2.9894 V
The expected load on the battery of the DS1306 is 550 nA @
3 V (pg 16).If you look over the BR2330 data sheet you find no indication it can rise above 3 V, unless you hike up the ambient temp well above 20 °C (which I don't).
I was wondering what range of voltages other members of this forum have observed from this battery. ============================================================ Gary Lynch | To send mail, change my | domain name from "no$pam" gary.lynch@no$pam.org | to "ieee". ============================================================