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DRV8832: PWM Frequency Tolerance

Danilo A.
Mastermind 25585 points
Part Number: DRV8832

Hi Team,

Can you please help us regarding the customer's inquiry below.

As described in datasheet, the internal PWM Frequency is 44.5 kHz. How stable should this frequency be and what is the expected tolerance-range? We drive brushed DC motors with a driving-time of about 60ms. Some Drivers (DRV8832) are producing only about 39.1...39.4 kHz (during the driving time) others are much closer to 44.5 kHz. My investigation shows, that the frequency is not depend on connected motor and is also not depend if no motor is not connected at all.  I have to define the testing parameters for the endtest system. Have you any recommendation?

I understand from the E2E thread below that the internal PWM frequency of DRV8832-Q1 (automotive grade) will vary from 30.4kHz at +90C degrees (using 2.9V at 85C) to 58.9kHz at -40C (using 6V). Is this also applies to the catalog device, DRV8832? 

e2e.ti.com/.../drv8832-q1-pwm-transient-period

Thank you for your support!

Regards,

Danilo

  • 0
    TI__Guru 54695 points

    Danilo,

    Good find on e2e!  Yes, this information will also apply to the standard catalog device.  

    Regards,

    Ryan

  • 0 in reply to Ryan Kehr
    TI__Mastermind 25585 points

    Hi Ryan,

    Thank you for the confirmation. We have received this feedback from our customer.

    I did my investigations at 25°C with a driving time of 60ms (the Tj of DRV8832 does never heating up that much).
    Inbetween same environmental condition, there are DRV8832 driving PWM at 44.5 kHz, others on 39.2kHz. This is more than 10% deviation. Is that common?
    Have you any documents, description or characteristics about PWM drift? Where can I find it?

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Guru 54695 points

    Danilo,

    I am not following above.  

    , there are DRV8832 driving PWM at 44.5 kHz, others on 39.2kHz. This is more than 10% deviation. Is that common?

    Maybe a typo in there or something.  Is he saying some devices are at 44.5kHz and others are at 39.2kHz?  Or does the PWM drift during operation?  

    Regards,

    Ryan

  • 0 in reply to Ryan Kehr
    Prodigy 50 points

    Hi all

    I try to clarify:

    We use the DRV8832 on our PCB's. I measured and compared the PWM Frequency on different PCB's with:

    - same schematic and same layout. 
    - same ambient temperature
    - same Voltage
    - same Motordriving time (60ms)
    - same amount of Motordriving cycles (about 5 cycles inbetween 30 seconds), therefore no relevant heating-up

    The PWM Frequency (generated from DRV8832) on the most of our PCB's is around 44.5kHz during the whole Motordriving time. But there are  a few PCB's which are creating more than 10% lower PWM Frequency than 44.5kHz. Some of them are creating only 39.2kHz also during the whole Motordriving time.

    I changed the load from the different PCB's, but this is not affecting the PWM Frequency.

    I am amazed that there is such a large deviation.

    In the datasheet I did not find any information about the tolerance of the DRV8832 internal PWM Frequency Generator. If you have any information about that it would be helpful.

    Best regards

  • 0 in reply to user5131039
    TI__Guru 54695 points

    Hello,

    5V, 25C data shows a standard deviation of 1.49kHz with a typical of 44.7kHz.  

    The 39.2kHz value you are measuring is within ~3 standard deviations.  If you add in some small temperature variation, I believe what you are seeing is the realm of possibility across the distribution.

    Does your application work with this spread of frequency?

    Regards,

    Ryan