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DRV8886: About the use of DRV8886

Takanari Nishikawa
Prodigy 80 points
Part Number: DRV8886

I am thinking of using DRV 8868 with noncircular 1/2 step.

However, the output waveform does not rise when using noncircular 1/2 step. (See Attachments)
The rise time varies depending on the Alumi Capacitor . Is the capacity of the electrolytic capacitor considered as a factor?

Please let me know if you have any other concerns.

Iout: 1.3 A
mod: noncircular 1/2 step
Decay mode: Mixed decay: 30% fast

Iout_waveforms.xlsx

  • 0
    TI__Guru 56650 points

    Nishikawa-san,

    In normal case, the Non-Circular 1/2-Stepping Current is either 0 or 100%. But, with 100uF input capacitor, the current ramping edge is broken in the middle.

    1. Please also monitor the input voltage and xOUT to see the current drop due to the input voltage drop or the xOUT channel's FET is off.

    2. If the motor is in stall condition (hold the motor not move), is the current waveform changed? I want to know the motor's back EMF affects the output or not.

    Overall, the system wants a stable input. If the motor operation changes the input voltage too much, we should have more input capacitance to hold input stable.

  • 0 in reply to Wang5577
    Prodigy 80 points

    Mr.Wang Li

    Thank you for your reply.


    (1. Please also monitor the input voltage and xOUT to see the current drop due to the input voltage drop or the xOUT channel's FET is off.)
    →Please refer to the attached Excel (Difference in power supply).
    　I onfirmed that the waveform rises by using a Regulated DC power supply.

    (2. If the motor is in stall condition (hold the motor not move), is the current waveform changed? I want to know the motor's back EMF affects the output or not.)
    →Please refer to the attached Excel (Iout waveforms at motor is in stall condition).

    (Overall, the system wants a stable input. If the motor operation changes the input voltage too much, we should have more input capacitance to hold input stable.)
    →Due to the size of the board, a large capacitor cannot be inserted.
        I would like advice if there are other measures.


    Best Regards.waveforms_0212.xlsx

  • 0 in reply to Takanari Nishikawa
    TI__Guru 56650 points

    Nishikawa-san,

    Thank you for sharing the waveforms.

    1. Would you use zero ohm for decay mode setting? In this application, when the current amplitude goes up, it is slow to switch to the full current. So, I think we can use slow decay when the current from 0% to +100% or -100%. The slow decay can reduce the current ripple doesn't bring down the current too much in the middle.

    2. 300uF input capacitor has less input ripple than 100uF input capacitor. Also, the Itrip level is almost stable (same peak current point) with 330uF. The board layout is done and the schematic's component value is correct. I don't think we can update the layout to reducing the noise. I want to make RREF resistor and AVDD capacitor is very close to the IC and the power ground current doesn't flow on it.

    2. The last test, "Iout waveforms at motor is in stall condition (hold the motor not move)", does those two waveforms use the same input power supply?