DRV8841: DRV8841: No OCP function

Cherry Zhou

Part Number: DRV8841

Customer purchased DRV8841 on ti.com and it looks like it has no OCP function:
1. The current probe reads the current at the OUT terminal;
2. VM=24V, RsensA=RsensB=gnd, Vref=3.3V, AIN1=3.3V, AIN2==BIN1=BIN2=AI1=AI2=BI1=BI2=gnd, AOUT1 and AOUT2 serials potentiometer
3. The measured current in Iout is more than 4A, and the output is turned off after 350ms. Adjust the potentiometer, when Iout=3.7A, the OCP is not entered after 2s, after a while, OUT will be turned off and then turned on again, and the cycle is like this, and the time to turn on is also shortened.
He guesses it is to be TSD, he would like to know how long is the time to enter OCP? Why didn't he enter the OCP, and what' s wrong with the settings?

Best Regards,
Cherry Zhou

over 2 years ago

0 Pablo Armet over 2 years ago

TI__Mastermind 37683 points

Hi Cherry,

Can you share a waveform showing AOUT1, AOUT2, and nFAULT. Take one zoomed in near where the output is first turned off and one zoomed out showing a few cycles of the outputs enabling and disabling.

0 Cherry Zhou over 2 years ago in reply to Pablo Armet

TI__Mastermind 22235 points

The first two images are captured with the AIN1 trigger at the same time by two oscilloscopes, and the third is the second image of the waveform when zoomed in. (Note: Current probe 1mV=1mA)

Below are specific information. Thank you so much!

Best Regards,

Cherry Zhou

0 Pablo Armet over 2 years ago in reply to Cherry Zhou

TI__Mastermind 37683 points

Hi Cherry,

Thank you for the waveforms.

It doesn't seem to be an OCP fault since the outputs are re-enabled after some time. During an OCP fault, the fault will latch low until nRESET is toggled or VM power is cycled. I believe this is an overtemperature shutdown fault. As the device is disabled, the temperature decreases once it drops below the OTS threshold which will re-enable the outputs causing the temperature to increase again until OTS is triggered once again. This process will continue to repeat which can be seen on the waveforms.

I am checking with our team internally to confirm the OCP deglitch time and max OCP threshold. Expect a reply from me with this information by 24 hours.

0 Pablo Armet over 2 years ago in reply to Pablo Armet

TI__Mastermind 37683 points

Hi Cherry,

Apologies for the late reply.

I'm still working on finding the OCP deglitch time and max OCP threshold. However, I don't think what you are experiencing is an OCP event. The OCP deglitch time is typically in the µs range which is not the case here. As I mentioned in my previous reply, whenever an OCP fault is detected, the fault is latched and the device needs to be reset to resume normal operation.

This is an over-temperature shutdown fault. Due to the very high current and power dissipation, the device temperature can very well exceed the OTS threshold temperature. If you intend to drive the load at 4-A continuous, you will need to select another driver with higher current rating or setting the current regulation limit below 3A to reduce the device temperature.

0 Cherry Zhou over 2 years ago in reply to Pablo Armet

TI__Mastermind 22235 points

Hi Pablo,

Thanks for your response.

Customer also thinks this is over temperature protection rather than OCP, because this phenomenon is different from the OCP phenomenon described in the manual. During use, the maximum power supply current can reach 4.5A. When the load is close to 4.5A, there is no OCP phenomenon described in the manual.

Thanks,

Cherry