• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 30 subscribers
  • Views 700 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.

DRV8874-Q1: DRV8874 Cycle-By-Cycle Current Chopping problem

Ziqi Yang
Prodigy 90 points
Part Number: DRV8874-Q1
Other Parts Discussed in Thread: DRV8874

Hey there

I am using DRV8874 for testing, about the function of Cycle-By-Cycle Current Chopping (7.3.3.2.2), datasheet mentioned  'This allows for additional control of the current chopping scheme by the external controller', I wonder how should I involve external controller inside of this to make current provided by chip be a stable value regardless of load added on shaft is always changing, as I want it to work in current control mode. 

I am now using fixed off time Current Chopping function to limit the maximum current, but I cannot achieve current control.

Thanks

  • 0
    TI__Expert 8985 points

    Hi Ziqi,

    The benefit of this cycle by cycle mode in terms of an external controller is the ability to re-enable the load drive after a positive control input edge change after the current regulation has been entered.

    An example to providing a stable current value, say Itrip is 1 A, is that, when the Iout > Itrip, cycle by cycle current regulation is entered and the nFAULT flag will assert low. The controller can use this nFAULT change as an interrupt and change the duty cycle of the control inputs so they reset it back to positive when the current reaches a desired value. You can can acquire the di/dt of the current through testing when in slow decay after Itrip is reached. Note that a study of current magnitude and the di/dt must be done to correctly do such an implementation

  • 0 in reply to Hector Hernandez Luque
    Prodigy 90 points

    Hey Hector

    Thanks for replying, if I understand it right, this is how I implement this cycle by cycle function: use fault signal edge changing as an external interrupt input to MCU, as in this mode the nFault signal will not affect the other functions, and the reason for acquiring di/dt is to according to it and adjust system response time, am I right?

    Regards

    Ziqi

  • 0 in reply to Ziqi Yang
    TI__Expert 8985 points

    Hi Ziqi,

    That is correct.