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DRV401: Probe Frequency

ttd
Mastermind 8110 points
Part Number: DRV401

Dear Technical Support Team,

I have some questions about the field probe oscillation frequency.

1.

The datasheet describes 310ns(max) for "Minimum Probe Loop Half-Cycle".

So is is correct that  one cycle means 610ns(1.6MHz)?

2.

The datasheet describes that the recommend  field probe oscillation frequency is from 250kHz to 500kHz.

 Is it possible to use over 500kHz? 

3. What specification does  increasing  field probe oscillation frequency changes getting worse? 

4. Apart from 3 , could you show the demerit to increase field probe oscillation frequency?

5. Could you show how do the  field probe oscillation frequency  and PWM frequency be decided?

    Is it related with L value of probe coil?

    

Best Regards,

ttd

  • 0
    TI__Mastermind 29710 points

    ttd,

    Thanks for asking your questions on the forum.  I will get back to in a day or two as I need to confirm with colleges.

  • 0 in reply to Javier Contreras4
    TI__Mastermind 29710 points

    TDD,

    Please see my replies below.

    Before reading on to my replies to your questions please consider the following. You may be getting a large frequency because the control loop could be connected in a positive feedback loop. To fix this simply reverse the connection of your compensation coil. If you do not have a feedback system (compensation coil) you could also get this large frequency.

    1) This is correct in that the probe excitation will oscillate at a frequency of 1.6MHZ typically when it is saturated. This is the minimum for the DRV401 to make the decision if the field probe is saturated. During normal operation the probe should take longer than this time in order to not hit the maximum oscillating frequency.

    2) Yes. This has to do with the determination of when the probe has saturated and the DRV401 determines (with internal comparator) it must change the polarity.

    3) There will be increase in the offset and offset drift of the sensor, because small internal timing errors and noise in the duty cycle processing of the probe will play larger role. This will also limit the correct decision if the field is too high causing the output to saturate. If you are close to max oscillation frequency the DRV401 can assume the probe is saturated with an external field and cannot recover. The issue is you need to design around all variation of a field probe. With inductance and resistance of probe changing with temperatures you do not want to be close to max frequency.

    4) I am not sure I think Item #3 with saturation detection is major concern for robustness over possible temperature and process variation. Incorrect saturation detection may cause a latch-up (phase-reversal) of the feedback loop and at the output.

    5) Yes, but the L-value is significantly dependent of the saturation of the core and how it behaves along with the field probe resistance. See this section of the datasheet

  • 0 in reply to Javier Contreras4
    Mastermind 8110 points
    Hi Javier,

    Thank you for your reply.

    I think that increasing around 1.6MHz is not recommend.
    If I have an enough margin(temperature characteristics of probe coil ) of frequency such as 800kHz , Do you think that the function work well? Of course, I need to pay attention to increase the offset and drift. I need to enough evaluation to work it.

    Best Regards,
    ttd
  • 0 in reply to ttd
    TI__Mastermind 29710 points

    Hello TTD,

    Yes, I should all work.  Like I mentioned you need to pay attention of the saturation at extreme conditions to make sure the feedback system is still working. There are a few parameters that change with temperature and the saturation of the core and its parasitic values will change.