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DRV8825: Could you tell me about DRV8825?

Pokkun
Genius 4695 points
Part Number: DRV8825
Other Parts Discussed in Thread: DRV8886AT, DRV8886

Hi,

I have some questions about DRV8825.

On the customer’s application, STEP frequency is changed during operation.

The current is distorted while low STEP frequency, but no problem while high STEP frequency.

To improve above, the decay mode need to be changed between mixed and fast.

Following current waveform shows same STEP frequency(500Hz) and different decay mode.

To change decay mode from mixed to fast, the current distortion will be disappear.

＜Question＞

(1)Can I change decay mode between mixed and fast without RESET during operation?

(2) Can I change decay mode between mixed and fast with RESET during operation?

(3) Do you have suggested schematic for changing decay mode between mixed(DECAY=open) and fast(DECAY=high)?

Best regards,

Masumi Sekiguchi

  • 0
    TI__Genius 14485 points
    Hi Pokkun,

    You should be able to change the decay setting at any time. The decay setting is selected by the state of the DECAY pin. You can set it to low, high, or Hi-Z states. Typically, you can change between these states by using a microcontroller GPIO pin. To set the pin to Hi-Z, just change the GPIO to an input.

    You may also want to check out our DRV8886AT, which has some smart tuning features called dynamic decay and ripple control. With these settings, your stepper should stay tuned over the whole range of speeds. Here's the link to a blog I wrote on this topic:

    e2e.ti.com/.../getting-smart-about-stepper-tuning
  • 0
    TI__Guru 56650 points
    Sekiguchi-san,

    According to the datasheet description, "when a motor winding current has hit the current chopping threshold (ITRIP), the DRV8825 will place the
    winding in one of the three decay modes until the PWM cycle has expired. Afterward, a new drive phase starts."
    I would think I can change decay mode between mixed and fast during operation. But, the new decay mode is applied on next PWM switching cycle. You may add a switching between 3.3V and Decay pin to switch mixed decay to fast decay.

    Also, you DRV8825 mixed decay uses a fixed period of time (75% of the PWM cycle) to do the fast decay. DRV8886 mixed decay uses the winding current to decide the fast decay timing. So, I would think DRV8886 doesn't need frequently switch the decay mode.