I did the first pre-production with K60 micro.
some boards are ok.
In some other I have this problem:
I set date/time at the first power up. All ok.
I power down board.
At the next power up date/time remains with values i set at the first power up (RTC module stopped).
- 32K oscillator is ok
- Battery voltage ok (3V)
- Board Vcc 3.3V
- Vbat pin voltage is ok
- tested board with 100nF and 10uF between Vbat pin and GND
- 2 BAT54 diodes to decouple 3V from battery and 3.3V from board regulator
- If I supply RTC module with external 3.3V supply instead of 3V battery it's all ok
- K60P144M100SF2 doc gives 1.71V as min. RTC battery supply voltage. Using battery I have 3V-(BAT54 drop)=2.8V
- On K60P144M100SF2 I found the min. value of VRFVBAT (VBAT voltage required to retain the VBAT register file) as TBD
Any ideas on how to solve the problem?