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DRV8825: Setting DECAY for DRV8825

user6116743
Prodigy 10 points
Part Number: DRV8825

Hi,

We are using stepper motor driver DRV8825 in our project.

Stepper motor type we are using in our project is 4 lead bipolar type.

When DECAY is set to Lo (low speed) and the reference voltage is gradually increased to reach a specific voltage (about 180 mV),

the holding force (motor drive current) during excitation immediately increases.

After that, even if the reference voltage is changed, the excitation holding force does not change.

In order to make the holding power of excitation variable, it is necessary to once set the voltage to 0V and set DECAY to Hi (high speed).

We have probed DIR, STEP, FAULT pin of driver IC but no issues were observed.

When DECAY is set to Hi, the holding power changes as the Ref level changes as expected.

Are there any restrictions on when to set DECAY?

Please let us know what is causing the DRV8825 to behave like this. 

Thanks,

Seiya

Hi,
We are using stepper motor driver DRV8825 in our project.
Stepper motor type we are using in our project is 4 lead bipolar type.
　
When DECAY is set to Lo (low speed) and the reference voltage is gradually increased to reach a specific voltage (about 180 mV), the holding force (motor drive current) during excitation immediately increases.
After that, even if the reference voltage is changed, the excitation holding force does not change.
In order to make the holding power of excitation variable, it is necessary to once set the voltage to 0V and set DECAY to Hi (high speed).
We have probed DIR, STEP, FAULT pin of driver IC but no issues were observed.
　
When DECAY is set to Hi, the holding power changes as the Ref level changes as expected.
Are there any restrictions on when to set DECAY?
Please let us know what is causing the DRV8825 to behave like this. 
　
Thanks,
Seiya
  • 0
    TI__Guru 56650 points

    Seiya,

    "After that, even if the reference voltage is changed, the excitation holding force does not change."

    The holding force is related the winding current. In slow decay mode, the winding current drops very slow because only a small switching FET's I*R drop voltage is applied to the winding to reduce the winding current. Ldi/dt=I*Rds_on

    To get a quick current drop, please try mix decay and fast decay to see it can meet your requirement.