DRV8251: Current regulation gain

Hi Pablo:

But our end customer use 24V and 48V, the Itrip has difference results.

They will provide the waveform for us tomorrow.

Would you please let us know how you get the figure 7-9 of datasheet?

Can you let us know the measurement processes?

I think will can ask our customer to do the same processes when Vvm=24V and 48V then compare with datasheet.

Please let me know your recommendations.

Thanks a lot.

Hi Statham,

Will look forward to viewing the waveforms. 

Statham Su said:

Would you please let us know how you get the figure 7-9 of datasheet?

Let me talk with our test team to get the details.

Regard,

Pablo

Hi Pablo:

Please refer customer measure results as below.

We did another test Vref = 1.13 and Rsense = 0.62 with 48V, the expected motor current is 1.13/10/0.62=182mA but the measured value is still over 500mA.

Use 24V and Rsense 0.43 (we don’t have 0.375) and this indeed can control the motor current to 228mA.

Is it possible we set a maximum Vref for the motor current (for example: 1.5A) and change to use PWM for (IN1/IN2) to control the motor current?

Please let us know your recommendations.

Thanks a lot.

Hi Statham,

Can you provided a zoomed in waveform of the top waveform. 

Regards,

Pablo

Hi Pablo:

Please refer below waveform.

1-1_DRV8251 48V AVG Current_4ms

1-2_DRV8251 48V Peak Current_4ms

1-3_DRV8251 48V AVG Current zoom_4ms

1-4_DRV8251 48V Peak Current-zoom_4ms

Pablo Armet said:

Let me talk with our test team to get the details.

Did you get the feedback from your teammate?

Please let us know your recommendations.

Thanks a lot.

Hello!

Pablo is out one additional day today, but back tomorrow.  He will respond then.

Regards,

Ryan

Hi Statham,

the current waveform is quite noise. This also means that the output voltage and SENSE voltage is noisy as well. If the SENSE voltage is noisy, it can cause the regulation loop to not work as intended. Can you try to add a small capacitor in parallel to the SENSE resistor. about a 10nF capacitor should be fine. 

Regards,

Pablo Armet

Hi Statham,

Any updates from your side?

Regards,

Pablo Armet

Hi Pablo:

About your recommend, "add a 10nF capacitor in parallel to the sense resistor".

Please refer below figure.

I re-summary our questions again.

Our end product is printer, we have recycle motor and provider motor.

When the motor rolling without paper, the current is around 250mA, when the motor rolling without paper, the current is around 1000mA,

Below is our schematic.

We change R1001 and R1002 to 0.43R, VM voltage use 24V and 48V.

And follow below formula to calculate the current regulation.

When using 24V, the real current meets the current regulation spec of datasheet, which is around 230mA.

When using 48V, change R1001 and R1002 to 0.62R, the real current is around 500mA, which didn't meet the spec.

When using 48V, change R1001 and R1002 to 0.27R, the real current is around 500mA, which didn't meet the spec.

That above issues are what we want to know.

It's why we want to know how to get it.

Pablo Armet said:

Statham Su said:

Would you please let us know how you get the figure 7-9 of datasheet?

Let me talk with our test team to get the details.

Would you please try it on EVM at your side??

We real want to know the results.

Looking forward your feedback.

Thanks a lot.

Hi Statham,

I will run some experiments in the lab to confirm the results and understand the root cause. I will provide my report within 24 hours.

Regards,

Pablo Armet

Hi Pablo:

How about the tested results?

Looking forward your feedback.

Thanks a lot.

Hi Statham,

Apologies for late reply. I didn't have the chance to go to the lab and test this yet. The past three day we had an ice storm in Dallas making driving to the office dangerous. I will get the results by Monday of next week.

Thank you in advance for your patience.

Regards,

Pablo Armet 

Hi Statham,

I confirmed the results in the lab. I'm reaching out to our design team for more information on how the VM voltage affects the current regulation.

Regards,

Pablo Armet

Hi Pablo:

Did you get the feedback from your design team?

We need your update for us.

Thanks a lot

Hi Statham,

Apologies for late reply.

I have not resolved this issue yet. I will work to have a final answer by Monday of next week.

Regards,

Pablo Armet