• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 30 subscribers
  • Views 584 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.

DRV8871: Does not limit in-rush current

Paul_Marco
Prodigy 165 points
Part Number: DRV8871
Other Parts Discussed in Thread: DRV8870

Hi there,

Our motor has steady state current of about 0.6A, but large start-up current >4A.

After reading the datasheet, we had assumed the DRV8871 would limit the in-rush current to the ITRIP current:

"The ability to limit current to a known level can significantly reduce the system power requirements and bulk capacitance needed to maintain stable voltage, especially for motor startup and stall conditions."

We are instead tripping the OCP and seeing a 3ms pulse wave form.

Is the DRV8871 only used for applications where the start-up current is less than Iocp ~3.6A?

  • 0
    TI__Guru** 114905 points
    Hi Paul,

    The device has overcurrent protection that can activate when the current is above 3.7A for more than the OCP deglitch time.

    Itrip is a separate circuit intended to limit the current during startup and stall conditions. Itrip is controlled by VREF and a sense resistor from ISEN to ground.

    What are the values of the sense resistor and VREF used in your application?
  • 0 in reply to Rick Duncan
    TI__Guru** 114905 points
    Hi Paul,

    Sorry, I answered for the DRV8870 above. Please allow me to correct myself.

    For the DRV8871:

    Itrip is a separate circuit intended to limit the current during startup and stall conditions. Itrip is controlled by the ILIM resistor.

    What is the value of the ILIM resistor used in your application? Ideally it should be less than approximately 20k to account for the variation of Vlim.
  • 0 in reply to Rick Duncan
    Prodigy 165 points
    Hi Rick,

    We set it to 18k and still tripping off the start.
  • 0 in reply to Paul_Marco
    TI__Guru** 114905 points

    Hi Paul,

    Using an 18k resistor with a max Vlim of 69 works out to 3.83A, above the 3.7A OCP limit.

    Please raise the Vlim resistor to 23k, or 3A as a test to avoid the OCP activation.

    If you are still seeing OCP activate, please provide a scope capture of the current.

  • 0 in reply to Rick Duncan
    TI__Guru** 114905 points
    Hi Paul,

    We have not heard from you in some time, and are assuming your issue has been resolved. If it has not, please reply to this thread. If the thread is locked, please select "+Ask a related question".