• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 30 subscribers
  • Views 1134 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.

DRV8870: DRV8870 OCP question

Minqi Zhao
Intellectual 1660 points
Part Number: DRV8870

Dear experts,

My customer is testing OCP function of DRV8870. They applied PWM signal to IN1 and set IN2 to high, when short OUT1 to OUT2 they find OUT1 and OUT2 remain high. It's strange because it seems that high side FETs are conducted but all FETs should be disabled based on datasheet. And it didn't resume or repeat fault cycle. Could you help to explain the question, or maybe it triggered another protection?

CH2:current of OUT1 terminal; CH3:OUT1; CH4: OUT2. CH4:OUT2

  • 0
    TI__Guru** 114905 points

    Hi Minqi,

    What is the VM voltage?

    What is the PWM frequency and Duty Cycle of the IN1 input?

    Can you provide scope captures of the second image zoomed in to 1ms/div and 5ms/div after the short?

  • 0 in reply to Rick Duncan
    TI__Intellectual 1660 points

    Hi Rick,

    VM voltage is 16.6V.

    PWM frequency is 15K，Duty Cycle is 46.34%.

    Besides, my customer found their boards now has OCP protection described in datasheet (p1 as below) under the same testing condition and solder method, but another board still has the same problem before that OUT1&OUT2 set high after short.

    Scope captures of the OUT1&OUT2 set high problem image zoomed in to 4ms/div (p2) and 800us/div(p3) after the short is attached as below.

    I attached the schematic before. Thanks for your answering!

  • 0 in reply to Minqi Zhao
    TI__Guru** 114905 points

    Hi Minqi, (NOTE: updated response due to hitting reply too soon. Updated information is in italics)

    The outputs are being PWMed, then appear to enter Hi-Z

    The image p2 shows what appears to be the outputs entering Hi-Z for ~160us, then driving for ~80us, and entering Hi-Z for many ms.

    The image could be overtemperature. 

    Would you ask the customer to:

    1) Recapture the images with a 1kOhm resistor to GND connected to one of the two outputs. This should cause both OUT1 and OUT2 to approach GND, confirming the outputs are Hi-Z.

    2) change the scale from 4ms/div to 100ms/div. Does the output begin driving again after hundreds of ms? This would indicate a possible overtemperature condition.

    3) Does the customer have the ability to measure the current in the motor during the PWM time? This will help determine if there is a possible overtemperature also. If possible please provide scope captures of the motor current.

  • 0 in reply to Rick Duncan
    TI__Intellectual 1660 points

    Hi Rick,

    Thanks for your reply, but there's some information I want to confirm.

    1)It is said in datasheet that if the die temperature exceeds safe limits, all FETs in the H-bridge are disabled. Since all FETs are disabled, so outputs should be low. But now outputs appear to enter Hi-Z, so what's the reason?

    Or the reason we need to recapture the images with a 1kOhm resistor to GND connected to one of the two outputs is to confirm whether the outputs are Hi-Z or just floating after  all FETs are disabled.

    2)It looks like outputs are still high after hundreds of ms.

    3)What's the exact meaning current in the motor during the PWM time?  Are you referring to current through output (CH2) but need to be zoomed in to 1ms/div and 5ms/div during the PWM time?

    Thanks a lot!

  • 0 in reply to Minqi Zhao
    TI__Guru** 114905 points

    Hi Minqi,

    Minqi Zhao said:

    1)It is said in datasheet that if the die temperature exceeds safe limits, all FETs in the H-bridge are disabled. Since all FETs are disabled, so outputs should be low. But now outputs appear to enter Hi-Z, so what's the reason?

    Or the reason we need to recapture the images with a 1kOhm resistor to GND connected to one of the two outputs is to confirm whether the outputs are Hi-Z or just floating after  all FETs are disabled.

    When the FETs are Hi-Z and the current no longer flows through the motor winding, the voltage at the outputs can be at any level. Adding the 1kOhm resistor to GND allows confirmation that the outputs are Hi-Z.

    Minqi Zhao said:
    2)It looks like outputs are still high after hundreds of ms.

    Thank you for the scope shot. We will have to investigate this further, and may have some additional questions.
    Can you provide the markings on the top of the package?

    Minqi Zhao said:
    3)What's the exact meaning current in the motor during the PWM time?  Are you referring to current through output (CH2) but need to be zoomed in to 1ms/div and 5ms/div during the PWM time?

    Yes, I am referring to the current through the outputs. There appears to be a current spike of ~8A at the time the event occurs. Can you zoom in to this area to determine what is occurring? Please show the outputs plus current.