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nxp pca2129t oscillator stops when switching form power supply to battery

Question asked by Thomas Erb on Aug 13, 2018
Latest reply on Aug 15, 2018 by Jose Alberto Reyes Morales


I have a clock device PCA2129T in use. In general the divice works fine. It is powered with 3.3V on Vdd and additionally connected to a battery voltage of 3.1V at Vbat.


Not always but in many cases after switch-off of the power supply at Vdd the oscillator stops. When I measure the battery voltage at Vbat it is constantly about 3V, so the clock should work. But the BBS pin shows a power breakdown to 0V and after a restart with normal power supply the readout of the OSF bit is set and the time within the device is lost.


Sometimes the device neither does stop oscillation nor BBS breaks down nor OSFbit is iset.


What could be reason(s) for this behaviour of the PCA2129T?


Thanks and regards