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DRV8886: Full-Scale Current over RREF Selection

Takashi Onawa
Genius 13200 points
Part Number: DRV8886
Other Parts Discussed in Thread: DRV8884

Hi Team,

I want to know how large Rref we can select for current regulation in DRV8886. Possibly, I want to set 70mA Ifs but 432kohm Rref didn't wok on DRV8886 EVM, Ifs was 180mA min.

Do you have "Full-Scale Current over RREF Selection" as following? I can find that in DRV8884 datasheet but not in DRV8886.

Regards,

Takashi Onawa

  • 0
    TI__Guru 56650 points

    Onawa-san,

    "Do you have "Full-Scale Current over RREF Selection" as following? I can find that in DRV8884 datasheet but not in DRV8886"

    Please check the latest datasheet:https://www.ti.com/lit/ds/symlink/drv8886.pdf  and https://www.ti.com/lit/ds/symlink/drv8884.pdf

    You actually post the DRV8886's "Full-Scale Current over RREF Selection" figure 11. DRV8884's Figure 11 is slight different than DRV8886's.

     "but 432kohm Rref didn't wok on DRV8886 EVM, Ifs was 180mA min."

    You put a higher Rref and get higher output current than Full-Scale Current over RREF Selection chart. That could be caused by the tblanking (PWM blanking time) limitation. When the high side FET is turned on, it will keep on at least tblanking time. If the motor inductance can not limit the winding current below the current setting, you will get a higher output current than the setting. There is one trick that we use to help regulate at lower currents. Setting TRQ to 1 (50%) changes the blank time to 1us instead of 1.5us, which can help regulation. BTW, accuracy is less because of the lower currents.