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BQ32000: RTC Time Drift During VBAT & VCC switchover time

Mohammed Azlum
Intellectual 835 points
Part Number: BQ32000

We are using BQ32000DR in our custom design board. We have connected Super Capacitor as VBAT supply. We are facing below issue while testing the RTC during the power cycle.

Issue description - RTC Time drift.
There is time drift while testing the RTC during couple of power cycle (immediate power cycle). This delay (or drift) observed as inconsistent pattern. Example, sometime delay is 5 sec, sometime delay is 10 minutes... so and so. Other-words, There is random delay in the RTC time during couple of power cycle.

Also please confirm, whether it is correct test case if we do the Power cycle continuously within 1 second switchover time between VBAT and VCC?

Wiring diagram is attached for your reference.

Regards,

Azlum

  • 0
    TI__Mastermind 28960 points

    Hello Azlum,

    First, are you waiting at least 1s after transitioning from backup power to VCC power? The time registers do not update for up to 1s after the switchover event. You mention something like this in your post, but it's not totally clear to me.

    Is there any relationship between the time drift and the error measured? For instance, if you cut VCC power for 10s and then restore it, do you see time drift ≤10s? Or does it seem random?

    Regards,

  • 0 in reply to Derek Payne
    Intellectual 835 points

    Dear Derek,

    Thank you for your reply. Let me explain more clearly.

    We are doing the multiple power cycling test (cut the VCC and restore it) continuously within 1 sec as mentioned in the diagram below. Below image is 1 power cycle diagram. I,e 1 sec is the time taken between each power cycle. When we did such multiple power cycling tests, we found that there is drift in the RTC time. Example, when we did power cycling 10 times (each power cycling time less than 1 second), then we found 10 second drift in the time.

     

    Since each power cycling time is less than 1 second and which is not meeting VBAT and VCC switchover time (1 second) criteria. Hence this time drift behavior occurred? Please confirm...

  • 0 in reply to Mohammed Azlum
    TI__Mastermind 28960 points

    Azlum,

    Thanks for the clarification. You understand correctly: since the switchover occurs for less than a second, the device never updates the value of the timer with the time passed during the duration on the backup supply.

    Regards,