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DRV8833C: Fast Decay/Slow Decay

Dylan You
Intellectual 2630 points
Part Number: DRV8833C

Dear Teams,

Have a nice day! I am helping my customer test DRV8833CEVM.

Could I ask the whether the "Stop" button is used for Fast Decay Mode or Slow Decay Mode?

Secondly, how could I obtain driven current waveform shown in the following picture?

Lastly, what is the purpose of the "Slow Down" feature for the EVM? It is only for adjust the motor speed, but not the decay mode?

Thanks!

Dylan

  • 0
    TI__Guru 56650 points

    Dylan,

    1. According to my test, the winding current ramp-up rate almost same as the ramp-down rate at low speed operation, I would think DRV8833CEVM uses fast decay.

    After click "stop" button, the winding current goes to zero.

    2. "Secondly, how could I obtain driven current waveform shown in the following picture?"

    I didn't see the picture. Please use "Insert file" and select your picture to upload.

    3. When the motor spins at high speed, you may not want to stop it hardly. So, you can slow it down first, and then stop it.

  • 0 in reply to Wang5577
    TI__Intellectual 2630 points

    Hi Wang,

    Thanks for your prompt reply!

    1. Because not matter it is fast decay or slow decay, the winding current will eventually drop to zero. Then how could I prove it is fast decay or slow decay by using the "Stop" button?

    2. I found there is a driven current waveform in the DRV8833C datasheet. Do you know how to test it with DRV8833C EVM?

    3. Based on my DRV8833C testing, the frequency of AIN1/AIN2 is 25Hz for Full Stepping with the starting speed. However, I have checked the DRV8833C EVM User Guide, and it states the motor starting speed is 100pps=100Hz at full micro-step. Am I testing incorrectly?

    Thanks!

    Dylan

  • 0 in reply to Dylan You
    TI__Guru 56650 points

    Dylan,

    1. Check the current ramp-down rate can confirm the fast decay. If it is slow decay, the voltage on winding terminal is zero. For an inductor, ideally, the current won't change if the terminal voltage is zero.

    2. Do you mean Figure 12? Put a few mH inductance load or a motor winding between OUT1 and OUT2. And then, use a current probe to measure the inductor current or winding current.

    3. Each STEP means each motor movement. A step motor has two windings. Any winding current changing could result a motor movement. How many AIN1 and AIN2 combination changes are in one AIN1 cycle time? According to your test waveform, one AIN1 cycle, AIN1 and AIN2 changes 4 times: Step 1: AIN1=1 AIN2=1; Step 2: AIN1=1, AIN2=0; Step 3: AIN1=0, AIN2=0; Step 4: AIN1=0, AIN2=1.

    So, STEP frequency is 4 times higher than AIN1 frequency.

  • 0 in reply to Wang5577
    TI__Intellectual 2630 points

    Hi Wang Li,

    Thanks for your support!

    For the second questions, I am asking Figure 8 on the DRV8833C datasheet showing in my last reply. Is that actually an expand version of xOUT1 (Output current waveform)?

    Thanks!

    Dylan