• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 30 subscribers
  • Views 660 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.

DRV8412/8432: how to control rotation direction and rotation speed?

fang circle
Prodigy 210 points

Hi all,

I'm a little confused by datasheet and some example code.

for motor control, I want to know,

1. under mode 1 (or mode 2), does one pwm control left bridge while the other pwm control right bridge? do i need do some special to avoid shoot-through? and how is direction controlled? and how is speed controlled?

2. under mode 4, does the motor rotate in one direction with duty cycle greater than 50%, and in the reverse direction with duty cycle less than 50%? and more deviation from 50%, greater speed?

3. when is mode 3 recommended? 

Any reply is greatly appreciated.

  • 0
    TI__Expert 8885 points

    Fang,

    Mode 1 and 2 are related to current limit functionality and difference between two is very well explained in over-current protection section of data-sheet. In summary mode-1 or CBC (cycle by cycle limit) protect the device by disabling the PWM for each switching cycle and get resets during every next PWM cycle. This mode is used to protect device during transient condition (such as starting, sudden load changes) whereas over-current shutdown does permanent shutdown of H-bridges.

     In both the above mode PWM logic of device control each half bridge independently i.e. PWM_A control both top and bottom switches of half-bridge A, if PWM_A is high top switch is on and OUT_A goes high and if PWM_A is low, OUT_A is low. Similar logic is applicable to remaining 3-hlaf bridges. Since device is controlling both TOP and Bottom switches, dead-time is build in device and it is in order of 5nsec sufficient to protect shoot-through  condition therefore there is no need for external shoot through protection.

     In both of above mode, you can drive two DC motor using two full-bridges. One full bridge can be constructed using Half-bridge A and B and other full bridge using Half-bridge C and D. For speed and direction control, you can opt either bipolar or unipolar PWM switching scheme. I do not know good on-line reference on this topic, but this is very well explained at chapter 7 sections 7.7 of textbook of “Power electronics-Converters Application and Design” by Ned Mohan, Udeland and Robbins. In summary Uni-polar PWM gives you 0 to 100 % PWM resolution for speed control in both directions whereas bi-polar PWM gives you 50% to 100% resolution because in this scheme at 50% duty cycle average output voltage applied to motor is zero and from 50% to 100% duty cycle motor rotates in one direction whereas from 50% to 0, motor rotates in other direction.

    Mode 1 and 2 gives you flexibility to choose either of above mode whereas mode 4 gives you fixed bi-polar switching pattern.

    In Mode 3 both the full-bridges can be paralleled to achieve higher current rating.

    Best Regards

    Milan

    Motor Application Team