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DRV8842: DRV8842 about the OCP issues

Mickey Zhang
Genius 12080 points
Part Number: DRV8842
Other Parts Discussed in Thread: DRV8832, DRV8830

Hi Team,

The customer is using DRV8842. When OCP occurs, the nFAULT outputs a low level. The customer would like to use this low level signal as a detection

signal in his design when the motor stalls. But he sets the ICHOP value. He made the mistake of ICHOP as the overcurrent value.

When he set ICHOP is 3.3A, then the motor stall current is test 2A.  When he set ICHOP is 0.66A, then the motor stall current is test 0.5A.

I would like to confirm the following information:

Q1: The OCP value is 6A. This value cannot be changed. Is my understanding correct?

Q2: What is ICHOP? Is ICHOP the output current for DRV8842?

Q3: Is the customer's idea correct? I don't think the customer use this low level signal as a detection signal.

Q4: Why is the motor stall current less than the ICHOP set value?

Best Wishes,
Mickey Zhang
Asia Customer Support Center
Texas Instruments

  • 0
    TI__Guru** 114905 points
    Hi Mickey,

    Q1: The OCP value is 6A. This value cannot be changed. Is my understanding correct?

    Yes, the OCP value cannot be changed.

    Q2: What is ICHOP? Is ICHOP the output current for DRV8842?

    ICHOP is used to limit the current through the load.

    Q3: Is the customer's idea correct? I don't think the customer use this low level signal as a detection signal.

    The customer may be able to use the concept in this application report: www.ti.com/.../slva858.pdf
    Current chopping should occur during starting the motor and stalls. Monitoring the outputs can be used to detect when the current is being regulated.

    Q4: Why is the motor stall current less than the ICHOP set value?

    How is the stall current measured? If using a meter, this is an average current. The ICHOP uses a peak current.
  • 0 in reply to Rick Duncan
    TI__Genius 12080 points

    Hi Rick,

    I would like to explain my words. I said the motor stalled. That is the motor is locked rotor.

    The customer uses a brush motor. The rated current is 1.5A for the motor. The rated voltage is 12V for the motor.

    He would like to detect the motor stall phenomenon and then the IC can output a FAULT signal to indicate that the motor stall phenomenon

    has been occurred.

    Can DRV8842 meet the customer's requirement? If it can, would you explain more about detecting the motor stall ?

    If it cannot, would you recommend a suitable IC?

  • 0 in reply to Mickey Zhang
    TI__Guru** 114905 points
    Hi Mickey,

    The DRV8842 does not have the ability to output a FAULT signal on motor stall.

    There are two devices in the portfolio that can detect stall, the DRV8830 and DRV8832. The operating voltage is too low. The stall detection method is similar to the reference design www.ti.com/.../slva858.pdf