DRV8876: MAXIMUM LOAD 2.2A

Hi Rodolfo,

With the values provided above, the current regulation threshold is set to ITRIP = 3.05A. This current regulation threshold is the maximum allowable current the load should draw. The current doesn't seem to be exceeding this value, which means the device is behaving as expected. The motor current doesn't have to reach the ITRIP value. The maximum motor current will depend on the resistance of the motor and voltage applied.

What's the stall current of the motor being used for testing?

Is the motor not able to spin?

Best,

David

Hi David

Thanks for the answer.
Sorry I was not precise enough in formulating the question.
1) DRV8876 works in "Fixed Off-Time Current Chopping" mode
2) the Ripropi has a 10nF capacitor in parallel
2) applying a variable load to the motor without limiting the current, this goes from about 0.5A to about 4.5A and beyond.
3) applying the same variable load to the motor but through the DRV8876 and with the Itrip at 3.05A the current rises to the maximum up to about 2.3A and then drops to about 1.0A due to the intervention of the protection.
4) but what I do not understand is why the Vpropi does not reach 2.5V but stops at about 1.9V. (1.9V/820ohm=0.0023mA * 1000= 2.3A)

The motor starts normally but does not have enough torque.
I cannot measure the stall current but it will be about 5A

Best regards

Rodolfo

Hi Rodolfo,

The current regulation should be set such that, VIPROPI doesn't reach or exceed VREF. If possible, could you try increasing VREF and reducing RIPROPI to reach the same ITRIP threshold?

Best,

David

Hi David

I tried these configurations

Vref=4,17V Ripropi 1500ohm =  2,0A instead of 2,8

Vref=2,50V Ripropi=0 = (remove the current regulation and only the OCP work) 2,2A

Best regards

Rodolfo

Hi Rodolfo,

How many units have you tested? Has this issue been seen with multiple devices? 

If you haven't already, I would also run these tests with a different power supply. Sometimes the power supply can limit the current. Be sure to set the current limit higher then desired current, in this case, around 4A to 5A. 

Best,

David

Hi David

ok I will test other devices and I will use another power supply on monday. I will reply asap

Best regards

Rodolfo

Thanks Rodolfo, Please comment once you have the waveforms.

Thanks,

Ibinu

Hi Ibinu

What kind of waveforms do you want to see ?

Best regards

Rodolfo

Hello Rodolfo,

It will be good to look at the waveforms including OUT, Vm Current  waveforms to understand the issue better.

Thanks,

Ibinu