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DRV8955: Spread Spectrum

Part Number: DRV8955
Other Parts Discussed in Thread: DRV8962,

Tool/software:

Can you describe the spread spectrum behavior of the DRV89xx series?  I am looking at controlling a proportional valve for a pressure controller, but I think the spread spectrum, if I am seeing it right on the oscope,, might make the valve "hunt", because the valve is going to response to the 'beat" of the spread spectrum.

Are there any similar current sense drivers that do not have spread spectrum or can have it defeated?

Thanks

Glen

  • Hello Glen,

    Spread spectrum modulates internal digital clock around +/- 10% to spread the peak fundamental frequency energy over a wider spectrum and bring down the peak significantly without any external mitigation components. This would affect the switch on/off edges at the output by a few 100ns. See below example output waveform from another H-bridge driver DRV8962 with a PWM 50% duty cycle. The dithering on the edges is constant regardless of the PWM frequency. If there is not PWM driver, i.e output on with 100% duty cycle then there won't be any edges for dithering. 

    See below capture from OUT1 with 20KHz PWM 50%. 

    See below capture from OUT1 with 200KHz PWM 50%. Like I mentioned before dither is constant and does not change with PWM frequency.

    When driving a BDC motor or a solenoid we've never seen this dithering make them "hunt" or produce any audible artifacts. Many of the hardware control H-bridge drivers have this feature permanently enabled. 

    If you are using current regulation feature of the DRV8955, the tOFF values also would be dithered because of spread spectrum. We've never seen this modulation affect a solenoid operation because tOFF is between 7 to 32 us and the dithering few 100ns. Spread spectrum also modulates charge pump switching frequency to reduce EMI peak from charge pump switching.

    I am looking at controlling a proportional valve for a pressure controller

    How is the proportional valve position controlled? Would it be by current regulation? or PWM on/off duty cycle? or by driving a motor with position feedback? 

    Regards, Murugavel

  • Hello

    Thank you for the information.  I agree, dithering in the 100's of nS should be fine.

    In answer to your question, we like to regulate the valve position with current, in response to pressure/flow changes.

    Thanks

    Glen