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Sensing ITRIP event

James Lim1
Prodigy 40 points
Other Parts Discussed in Thread: DRV8834

I have look through the DRV8834 and family, and will like to know if there's any method to know (feedback to mcu) whenever an ITRIP condition occurs.

It seems to me that the SENSE resistors + amp is in place to detect a voltage > VREF to signal an ITRIP condition and stop the Hbridge, but there don't seem to be an output to signal that ITRIP occurs.

If there's no such functionality built in, I am thinking of sampling the Rsense with an external amplifer to tell the MCU about the ITRIP condition. Do you think that will work? When an ITRIP event occurs, does the ITRIP actually stop current flowing through the Rsense resistors? 

  • 0
    TI__Guru 55605 points

    James,

    You may be confusing Overcurrent Protection (OCP) with Current Control.

    For current control, the trip point is set by equation 1 on page 9 of the datasheet.  To understand how this current chopping technique works and the various decay modes, it is best to start reading on the bottom of page 8.  There is quite a bit of flexibility on how the H-bridge behaves when the trip point is exceeded and this depends on decay modes.  This detail can be found in the datasheet.  Under current control, there is NO method to detect when the device is chopping current.  This would need to be down by externally monitoring the voltage across the sense resistor as you mentioned.

    For over-current protection that works with a fixed minimum trip point of 2A, this operation is described under protection circuits on page 16.  If this protection is tripped on output shorts, etc....the nFAULT pin will cycle low indicating an over-current event has ocurred and the device will go into a 1.2ms retry period.  Normal operation will automatically resume if the short is removed. 

     

  • 0 in reply to Ryan Kehr
    Prodigy 40 points

    Thanks Ryan. 

    My main concern is the OCP fixed limit of 2A maybe too high for my application., considering the motor I am using has a max peak current of 0.25A. Assuming I use only full step, I'm looking into using the ITRIP as an indicator. do you see a possible solution for this? :)

    James

  • 0 in reply to James Lim1
    TI__Guru 55605 points

    James,

    Understand.  You can ratio VREF and Rsense per the equation in the datasheet to achieve 0.25A of current regulation in full step.  As an added precaution, you can monitor the voltage drop across Rsense with a comparator set to a higher trip point as you orginally noted.

     

  • 0 in reply to Ryan Kehr
    Prodigy 40 points

    OK, thanks for confirming!