DRV8825: DRV8825 over current protection

Hi Elyasaf,

Thanks to your answer

Further to our correspondence

I plan the "I chop" to 4A, I work in full step mode so the real current is 2.8A.

Setting the Ichop to 4A in full step will set the current limit to 2.8A. 

In high temperature sometimes the driver stop to work and I got nfault.

Only reset resume the driver working. So I understand that I got OCP (over current protecaiotn).

In our  correspondence I understood from you that I can work with 4A "I chop" because that in full step mode its 2.8A. And it shouldn't be a problem with OCP.

Did I plan correct?

You did plan correctly, and this does appear to be an OCP event.

Can you provide your schematic? Ideally we would like to see all the circuitry connected to the DRV8825 (resistors, capacitors, mcu, etc.).

If necessary, we can make arrangements to share it privately.

Have you measured the current to confirm the device is regulating properly?
Are you using mixed or fast decay? If using slow decay, the current may exceed the desired Ichop and create an OCP event.

Have you measured the current to confirm the device is regulating properly?

Yes. The current is 2.8A.

Are you using mixed or fast decay? If using slow decay, the current may exceed the desired Ichop and create an OCP event

Mixed decay.

The problem increase in high temperature.

Hi Elyasaf,

Can you provide your schematic? Ideally we would like to see all the circuitry connected to the DRV8825 (resistors, capacitors, mcu, etc.).

If necessary, we can make arrangements to share it privately.

Hi rick

• I send you the periphery of the driver schematic.
• DRIVER POWER=40V
• The control signals are stable with filters:.

DIR-: R=1K with 1nF

ENABLn : R=1K with 1nF
STEP : 1K with 10nF

STEP :My profile operation is 1.5 sec: 0.1 sec at 500 Hz. 0.3 sec from 500 Hz to 4 kHz , 1.1 sec at 4 kHz. (150~ RPM to ~1200 RPM)
mixed decay.

• also you wrote

" If using slow decay, the current may exceed the desired Ichop and create an OCP event."

i used mixed decay with the profile  mentioned above. Could it be the reason for the OCP?

Hi Elyasaf,

Thank you for the information.

Please try the following and report if this has any effect.

Please examine the nSLEEP pin looking for small negative pulses dropping below 2V prior to the nFAULT assertion. If the device drops below 2.2V, this could be interpreted as a logic low.

If you see this, please lower the 10k nSLEEP pullup resistor to 1k. There will be little effect on the overall current consumption, but lowering the nSLEEP pullup resistor can prevent the drop of the nSLEEP pin below a valid Vih level.

Hi Rick

Yes' there is negative pulses on the nsleep leg.

Can it stick the driver after the nsleep return to valid level?

thanks

Elyasaf

Hi Elyasaf,

Yes' there is negative pulses on the nsleep leg.

Can it stick the driver after the nsleep return to valid level?

Yes, a small negative pulse may cause the DRV8825 to incorrectly enter the overcurrent state.

It is important to maintain a logic high voltage on the nSLEEP pin. Lowering the value of the nSLEEP pullup resistor (1kOhm is recommended) should help maintain the nSLEEP voltage above the Vih level. 

Hi Rick

I put 1k pull up on the nsleep and it resolve the problem.

I still saw little negative pulse to 2.5V.

I put 0.5K pull up . The negative pulse drops to 2.8V.

I think that this resolve the problems.

1. Thank you !!!!

2. Is there any problem with 0.5K pullup?

3. Could  Ti write somewhere that there is connection between nsleep and OCP (over current protection) and also to put 1K pullup to the nsllep. I didn't see such a recommendation.

Thanks

Elyasaf