Comments on VBAT source switching circuit
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VBAT source switching circuit
This is VBAT switching circuit installed in one of my PCB for Timekeeping when VCC is not present.
The switching circuit is working as expected - when VCC is present, the current flows from D3 to VBAT and when VCC is not present, the current flows from J2 to Q6 to VBAT. After a month, we randomly checked the RTC coin cell battery (3V) and it was discharged to 1.6V and that's not normal because these batteries are supposed to work for years without changing.
Then I measured the current VBAT with VCC present = 3.117 and current is -2.251mA Without VCC, the VBAT is 2.8927V and current is 0.015mA (16uA)
In my observation, the negative current is flowing back to the RTC battery and hence degrading it. May be Q6 is not turned OFF properly.
I am not sure if that's what causing the issue. I tried simulating another circuit online. Can I use this circuit and replace the existing one ?
**Update - **
Here is the new circuit which is on the PCB and this circuit is causing battery drain.(ignore the top circuit)
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