DRV8840: OCP doesn’t work at the condition of 6A and 8ms

Shinichi Inoue

Guru 20496 points

Part Number: DRV8840

Dear Specialists,

My customer is encountering the same situation.

I would be grateful if you could advise.

---

According to the related thread, the conditions for an overcurrent event are commented as current >6A 3.75us±30%.

When the current is 6A or more for 4.875μs or more, overcurrent protection should operate

Could you please see the waveforms below.

(1) There is an 8ms time period exceeding 6A with slow decay(8Apeak), but the FET is not disabled and nFAULT remains high.
Overcurrent protection is not working.
Is this correct behavior?

(2) Or, if I use the DRV8840 brake function (Slow Decay), will the OCP (Overcurrent Protection) circuit not work?

(3) At this condition, is there a risk of device damage?

(4) "6.1 Absolute Maximum Ratings" states "Peak motor drive output current, t < 1 μS　Internally limited".
Is there a possibility that this condition will be violated?

---

I appreciate your great help in advance.

Best regards,

Shinichi

over 1 year ago

0 Jacob Thompson over 1 year ago

TI__Mastermind 22790 points

Hey Shinichi,

Give me another day to look into this and analyze the related threads:

DRV8840: DRV8840 motor drive IC OCP conditions
DRV8840: maximum OCP current and OCP decision timing - Variation ± 30%, the OCP could assert in as little as 2.6us. (Or as much as 4.875 us?)
DRV8840 OCP detection time - Worst case OCP time should be 3.75usec

Regards,

Jacob

0 Shinya Morita over 1 year ago

TI__Mastermind 34745 points

Hi,

Our expert is reviewing your questions. His feedback will be posted in a day or two.

regards

Shinya

0 Jacob Thompson over 1 year ago in reply to Shinya Morita

TI__Mastermind 22790 points

Hey Shinichi,

What is the state of the device inputs (PHASE/ENBL and DECAY) and nFAULT at the time of the OCP event? So we can see the state of the motor driver when this event occurs. The screenshot looks like the device might be in Hi-Z after the peak, and want to see state of nFAULT.

And can you post a new screenshot with the cursors showing the delta time where the current is above 6.0A?

Shinichi Inoue said:
(2) Or, if I use the DRV8840 brake function (Slow Decay), will the OCP (Overcurrent Protection) circuit not work?

OCP should work as long as the device is not already in Hi-Z:

Regards,

Jacob

0 Shinichi Inoue over 1 year ago in reply to Jacob Thompson

Guru 20496 points

Hi Jacob,

Thank you for your reply.

Could you please see attached file.

Slow Decay Waveform.pdf

The time for 6A is about 800μs.
However, nFAULT does not occur in the attached waveform.
Therefore, no error has occurred.

I'm guessing 6A is the lowest threshould, and the actual OCP threshold is much higher.

I appreciate your great help and cooperation.

Best regards,

Shinichi

0 Jacob Thompson over 1 year ago in reply to Shinichi Inoue

TI__Mastermind 22790 points

Hey Shinichi,

It looks like this event is happening AFTER the motor driver is done driving the outputs and has entered Coast/Hi-Z mode. The device wouldn't detect OCP during this time. This event is normal excess current from the inertial load of the motor after device outputs go Hi-Z.

Can you post an oscilloscope capture showing the states of PHASE and ENBL as well?

Regards,

Jacob

Motor drivers

Motor drivers forum

DRV8840: OCP doesn’t work at the condition of 6A and 8ms