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DRV8818: Stepper motor suffer from low position accuracy

Danilo A.
Mastermind 28880 points
Part Number: DRV8818

Hi Team,

We would like to ask your your help regarding our customer's inquiry below.

We have use the stepper motor driver chip to drive a unipolar stepper motor with following specification,

Part number: PJB42S33D16

Step Angle: 1.8 degree

Rated Current: 1.2

Resistance 2.4 ohm

Inductance: 2.3mH 

We will run the stepper motor with 6.7rps with driving voltage set at 25V and Max current trip at 1.2A.

We have place a infrared light sensor to measure the rotation speed of the stepper motor.

I have used the oscilloscope to measure the HOME and step signal with respect to the DHOME signal (signal from the infrared light sensor. We will notice the HOME and step signals are oscillating as shown in the figure below.

I have measure the phase current across, AOUT1 and AOUT2 and BOUT1 and BOUT2 as shown in the figure below,

 As from the measurement, the current waveform is incorrect and unlike the ideal current waveform for 2 phase full step 

Here is the schematic diagram

Regards,

Danilo

  • +1
    TI__Guru 56650 points

    Hello, Danilo,

    The output current waveform is correct to me. Since the output is an inductive load, the current change follows the inductor basic law: di=(Vcc * dt) / L. If the VCC is not very high or L inductance is high, the output current cannot be changed immediately. So, the output  takes some time from one level to another level.

    Regards,

    Wang Li