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BQ32000: BQ32000

jayashree
Intellectual 680 points
Part Number: BQ32000

Hi Team,

I am using the BQ32000DR RTC with FC-135 32.7680KA-A5 crystal , I had not mounted tuning capacitors as already there are 24pf internal capacitors. I am getting below mentioned error .

bq32k 0-0068: Oscillator Failure. Check RTC battery.
bq32k 0-0068: rtc core: registered bq32k as rtc0

I had connected CR-2032 battery as a VBACK supply,

I had powered on the board and set the time to the RTC IC and observed that time is incrementing and working as expected. Once when I power off the board and wait for while and power on the time observed is not appropriate (not updating as expected).

Why is this oscillator used? and Does this oscillator effect the timing?

With regards,

Jayashree.

  • 0
    TI__Genius 16845 points

    Hi Jayashree.

    Oscillator Failure is described under datasheet table 5.The device has an OF flag (oscillator fail) that is always initialized to high after power up. The flag should be cleared when you are initializing the RTC (setting the time). Then, you can monitor the bit in case there is oscillator fail event during operation. 

    If you power off the board, BQ32000 must have VBACK to keep counting time. After VCC is reapplied, you could read the time from the device again. 

    How long do you power off the system? What time is observed after VCC is reapplied?

    Kind regards,
    Lane

  • 0 in reply to Lane Boyd
    Intellectual 680 points

    Hi Lane,

    Thanks for the reply.

    Is the oscillator failure flag is set each time when we power off and on the board?

    When I am powering off, a battery of 3V is connected to VBACK to keep counting the time. Now actually we had made some changes in the code regarding oscillator and we are observing proper time now once I power off and on after some time.

    I have a question whether we need to stop oscillator and start every time during power on, or only for initial power on?

    With regards,

    Jayashree.

  • 0 in reply to jayashree
    TI__Genius 16845 points

    Hi Jayashree,

    Yes, OF flag is set each time BQ32000 powers up after total power loss. However, if you still have VBACK provided, OF flag should not when VCC is reapplied.

    The OF bit does not stop or start the oscillator, it only reports when the oscillator drops 4 consecutive pulses. You do not need to stop the oscillator. 

    Kind regards,
    Lane

  • 0 in reply to Lane Boyd
    Intellectual 680 points

    Hi Lane,

    In the design I had provided external tuning capacitors for the crystal. Once I removed the external crystal it is working as expected.

    Thanks for your support.

    With regards,

    Jayashree.