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DRV8832: That big differences in PWM Frequency depend on part?

user5131039
Prodigy 60 points
Part Number: DRV8832
Other Parts Discussed in Thread: DRV8214

Hi

We designed an electronic for driving an electromechanical actuator with a DC-Motor, driven by a DRV8832. On about 5% of our electronics, we measured a surprisingly high deviation of the PWM-Frequency.

Nominal Frequency written on datasheet is 44.5 kHz, but the measured Frequency of three of our deviating samples are:

  • 38.2 kHz (Sample 02)
  • 49.6 kHz (Sample 05)
  • 49.4 kHz (Sample 06)

If needed, I can post the measurements-pictures of the above samples.

Measurement Details and Explanations:

  • The duration of an Opening- and Closing-Sequence are 60 ms.
  • We measured the frequency at 10ms, 30ms and 50ms after start of a Sequence.
  • Labor Temperature is 22 °C.
  • No heating of electronic parts, because of less than 1 Sequence per Minute.
  • V_MOT is supplied over a stable Power supply with 4.50V

Results / Facts:

  • The measured Frequency is stable during the whole Sequence and is independent of Opening- or Closing-Sequence (independent of drive-direction)
  • Retries of measurement shows the same results (replicable)
  • The measured Frequency is not dependent on the load on OUT1 and OUT2.
  • The difference of PWM Frequency is caused by the DRV8832 itself (changing the DRV8832 to another electronic, shows the same results as on the electronic before).

Questions:

  • Are those big differences normal?
  • How can you explain a such great range of the parts characteristics?
  • What is the tolerance of frequency at 25°C?

Thanks for your help and explanations.

Joel

  • 0
    TI__Mastermind 19860 points

    Hi Joel,

    With V_MOT = 5 V, the tolerance of frequency at 25°C is a standard deviation of 1.49kHz with a typical of 44.5kHz.

    • 38.2 kHz (Sample 02) --> ~ 4 standard deviations 
    • 49.6 kHz (Sample 05) --> ~ 3 standard deviations
    • 49.4 kHz (Sample 06) --> ~ 3 standard deviations

    Does your application work with this spread of frequency?

    Best,

    David

  • 0
    Prodigy 60 points

    Hi David

    I don't undestand. What is the meaning of "standard deviation"? Have you documentation about this topic?

    What is the reason, why about 90% of our electronics are within the standard deviation (43.01...45.99 kHz)?

    Best regards

    Joel

  • 0 in reply to user5131039
    TI__Mastermind 19860 points

    Hi Joel,

    Yes, meaning a standard deviation (1.49kHz) from the typical internal PWM frequency of 44.5 kHz. 

    As you mentioned in your initial post 95% of the electronics are within the expected frequency range and only 5% (samples: 02,05,06) are considered outliers falling a few standard deviations outside of the expected PWM frequency. 

    This is expected behavior. If this is not suitable for your design might I suggest a newer family of drivers with the same functionality.

    Best,

    David

  • 0
    Prodigy 60 points

    Hi David

    Is there any official document of DRV8832, which is describing such an amount of percentage outliers with up to 4 standard deviations?

    Best regards

    Joel

  • 0 in reply to user5131039
    TI__Mastermind 19860 points

    Hi Joel,

    We unfortunately don't have any public documentation regarding this specific issue. 

    Is there a spec in particular you are looking for?

    Best,

    David

  • 0 in reply to David Medis
    Prodigy 60 points

    Hi David

    I would expect it in the datasheet, in chapter "Electrical Characteristics", where the "Internal PWM Frequency, fSW" is described (min and max).

    Or in a part-specific technical note, where the behavior of internal frequency is described. There you can also explain the frequency drift depending on temperature... for example...

    But the decision is up to you or the respective TI Tech Team.

    Best regards

    Joel

  • 0 in reply to user5131039
    TI__Mastermind 23431 points

    Hey Joel,

    Agreed that it would be nice if our datasheet had this data.  Unfortunately the best I can give you is another E2E post answered by someone more familiar with this part - https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1015206/drv8832-pwm-frequency-tolerance This part is very old so we don't have any plans to update the datasheet at this time, though I will look into it.  

    You mention this is a new design - the DRV8832 is a very old part, and we have many newer devices with updated features (and improved datasheets) that might better fit your application.  Can you take a look at the DRV8214? It works up to 11V / 4A (compared to DRV8832 7V / 1A), has internal PWM generation at selectable 25kHz or 50kHz, and is in a much smaller package size than DRV8832.  DRV8213 is a similar, cheaper alternative if you don't need the advanced features in DRV8214 such as speed/voltage regulation, position control, or internal PWM generation.

    Best,

    Jacob

  • 0 in reply to Jacob Thompson
    Prodigy 60 points

    Hi Jacob

    Thanks for your comments and proposals. As soon a redesign will be necessary, I then change to an newer driver type.

    Although my question is not completely answered, I will close this ticket.

    Thank you guys for supporting me.

    Best regards

    Joel