AnsweredAssumed Answered

Vbat & RTC problems

Question asked by corrado carini on Jun 21, 2012
Latest reply on Jul 17, 2012 by EARL GOODRICH

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).


Some considerations:

- 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?