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DRV8908-Q1: Flyback, EMI/EMC, 2kHz audible noise, free-wheeling

Matteo
Prodigy 80 points
Part Number: DRV8908-Q1

Tool/software:

 Hello, I need your advice on a few points:

1. I have connected a solenoid valve to an output of the driver in this configuration (see image). Is it recommended to add a flyback diode and a capacitor between output and ground?
2. What do you recommend to improve performance regarding EMI/EMC?
3. How can I solve the problem that the PWM (2 kHz) generates audible noise?
4. Currently, free-wheeling is active. Do you recommend leaving it like that?
5. In the case of a PC fan connected in the same way, do you suggest gradually increasing the duty cycle instead of starting it at maximum?



Thank you. Best regards

  • 0
    TI__Mastermind 24440 points

    Hi Matteo,

    Matteo said:
    I have connected a solenoid valve to an output of the driver in this configuration (see image). Is it recommended to add a flyback diode and a capacitor between output and ground?

    how fast does the energy in the solenoid need to decay? If you have some timing requirements a flyback diode will help to dissipate the energy quickly so that the timing requirements can be met otherwise simply using a slow decay by turning on the low side FET will work.

    Matteo said:
    What do you recommend to improve performance regarding EMI/EMC?

    Is there a frequency that you are targeting to improve? This document has some suggestions you can look through for general tips: TIPL_motor drivers_EMI design_tips

    Matteo said:
    How can I solve the problem that the PWM (2 kHz) generates audible noise

    This is likely caused by the coil in the solenoid itself. Using a PWM frequency above 20kHz will be the best solution so that the noise generated is not audible.

    Matteo said:
    Currently, free-wheeling is active. Do you recommend leaving it like that

    The suggestion depends on how you want the half bride to act during the PWM low periods. If you want the non-driven FET to remain off during the low periods, then disable freewheeling otherwise leave freewheeling enabled so the non-driven FET will enable during the PWM low period.

    Matteo said:
    In the case of a PC fan connected in the same way, do you suggest gradually increasing the duty cycle instead of starting it at maximum

    I would recommend gradually increasing the duty cycle. While setting the duty cycle to max can work the fan will have smoother startup if the duty cycle is ramped.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Prodigy 80 points

    Hi Joshua,

    Thank you for your reply.

    1. I have no requirements yet, I evaluate the driver. The actuation frequency I think is slow enough. I think a slow decay is a better solution. With an external diode I have seen more noise with PWM active.

    3. Isn't 2 kHz maximum frequency for the DRV89xx-Q1?

    4. Can you explain the pros and cons to me?

    2. and 5. Thank you for the link and tipp.

    Thank you for your support.

    Best regards,
    Matteo