• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 30 subscribers
  • Views 135 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV8834EVM: overshoot and undershoot on AOUTX pins, M0 pin internal pulldown

Ken Zhang
Expert 3595 points
Part Number: DRV8834EVM
Other Parts Discussed in Thread: DRV8834

Tool/software:

Hi,

Customers have encountered some questions while testing the DRV8834, please help them.

1.During the motor rotation, there will be an overshoot and undershoot on Aoutx or Boutx pins, their peak voltage is depend on the current periods. The waveforms in next slide are tested with Vbus = 3.3 volts.The overshoot is up to 4 volts and undershoot is down to -0.7V.

Note: “Tip and Barrel” approach is already used to measure SW voltage waveform.

Question 1: Why there is such a phenomenon, whether it will cause IC anomalies and how it should be eliminated.

2.In DRV8834 datasheet, M0 and M1 Pins have nominal pull-downs internally, when M0 pin is floating and MO pin voltage is measured  at 1.4 volts instead of being internally pulled low.

Question 2: Is this abnormal?

overshoot and undershoot voltage on Aoutx _Boutx Pin.pptx

  • 0
    TI__Mastermind 45445 points

    Hi Ken,

    Thank for the post. 

    Ken Zhang said:
    1.During the motor rotation, there will be an overshoot and undershoot on Aoutx or Boutx pins, their peak voltage is depend on the current periods. The waveforms in next slide are tested with Vbus = 3.3 volts.The overshoot is up to 4 volts and undershoot is down to -0.7V.
    Ken Zhang said:
    Question 1: Why there is such a phenomenon, whether it will cause IC anomalies and how it should be eliminated.

    This is due to the inductance of the windings and back EMF of the motor which could generate a positive voltage above VM and a negative voltage below 0V. This will be evident during the dead-time during HS and LS FET conduction transition. During dead-time the FETs will not conduct, however their body diodes will conduct to VM or GND hence the diode drop of +0.7V or -0.7V. The device is designed to withstand these spikes, there should be no issues. 

    Ken Zhang said:

    2.In DRV8834 datasheet, M0 and M1 Pins have nominal pull-downs internally, when M0 pin is floating and MO pin voltage is measured  at 1.4 volts instead of being internally pulled low.

    Question 2: Is this abnormal?

    Yes, this is normal. The M0 pin design is different because it is a tri-level input. For the Z level setting 1.4 V is detected as an open pin to set the mode. Thank you.

    Regards, Murugavel