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Compiler/TMS320F28035: BQ32002 oscillation not work normally

Wen-Gou Lin
Prodigy 220 points
Part Number: TMS320F28035
Other Parts Discussed in Thread: BQ32002

Tool/software: TI C/C++ Compiler

Here is my cricuit of BQ32002

A 32.768kHz osicllator（CM7V-T1A_12.5pF） whose capacitance is 12.5pF is connected between pin1 and pin2 of BQ32002. But it seems the  osicllator is not 

oscillating perfectky. Below is the waveform between pin1 and pin2 of BQ3200. Any suggestions?

  • 0
    TI__Mastermind 18070 points

    Hi Wengou,

    My coworker will get back to you tomorrow.

    Regards,

    Hao

  • 0 in reply to Hao Z
    TI__Genius 16845 points

    This oscillator has the correct capacitance, is it meeting the other specifications in datasheet table 6.3? Connection to the oscilloscope does appear to indicate that oscillations are occurring, thus it is unlikely there is some issue with the crystal oscillator. 

    Probing a crystal oscillator may not always match your expectations due to several reasons. The capacitance of the scope probe will impact the oscillation. Too much probe capacitance will stop the oscillations. In this measurement, we can see the frequency is too low.

    Alternatively, you might use the OF bit (oscillator fail) to check for stopped oscillation. Remember to clear OF after power-up because it will initialize to true

    Kind regards,
    Lane

  • 0 in reply to Lane Boyd
    Prodigy 220 points

    Below the link to my oscillator(Micro Crystal /CM7V-T1A-32.768kHz-12.5pF-20PPM-TA-QC)

    Do it meet the requirement of BQ32002?

    cm7v-t1a-1085727.pdf

    May you show me the block diagram of the internal 32kHz Oscillator as shown below?

    What will happen if we don't clear OF bit during initialization stage?

  • 0 in reply to Wen-Gou Lin
    TI__Genius 16845 points

    The XTAL is meeting the datasheet requirements.

    I cannot share the block diagram. This an older device with limited design support.

    If OF is not cleared during initialization, the value will remain at 1, and you will not be able to detect subsequent oscillator failures

    Kind regards,
    Lane