DRV8881: Under VREF=0.3V

Hello David,

Thank you for your answer.

I have an additional question.

Normally, formula (1) is used to calculate Itrip. But I found past E2E.
Here, it is written to calculate Itrip from Fig9 if VREF is not 3.3V.

https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/805649/drv8881-vtrip-on-figure9-and-the-chopping-current/2983689#2983689　

However, when Itrip is actually measured, it is close to the value calculated using equation (1).
Did you modify any devices?
When VREF is 3.3V or less, which calculation formula is correct for Itrip, formula (1) or Fig9?

Best Regards,
Ishiwata

Hi Ishiwata-san,

The device has not been modified. 

You are correct to use equation (1) to calculate ITRIP. Figure 9 provides estimated values of Vtrip vs Vref with varying TRQ(%) settings. Depending on the settings of TRQ(%) and sense resistor these values should be similar but the formula is more accurate. 

Best,

David

Hello David-san,

Thank you for your answer.
I have an additional question. If I want to set the motor current to 0, is it okay to set VREF=0V?
Is VREF=0 prohibited because it is outside the recommended range?
If I want to set the motor current to 0, is it correct to control it with another terminal?

Also, if VREF is 0.3V or less, please tell me how much it varies.
I think it's difficult to give a clear answer. Please let me know, even if it's just a rough estimate.

Best Regards,
Ishiwata

Hi Ishiwata-san,

Setting VREF = 0 will set the full scale chopping current in the H-bridge to 0. This will allow no motor current, however it is recommended to put the device into sleep mode by setting nSLEEP pin low. 

It is difficult to say for sure how much VREF will vary when it is less than 0.3V. It is recommended to test for such conditions using one of our DRV8881EVMs.

Best,

David

Hello David-san,

Thank you for your wonderful support.

Thanks for the answer about motor current 0.

Regarding the change when VREF is less than 0.3V, since there is no EVM here, can you check it yourself?
I know this is an impossible request, but I appreciate your cooperation.

Best Regards,
Ishiwata

Hi Ishiwata-san,

I will track down an EVM to test in the lab and reach out next week with my results. 

Best,

David

Hi Ishiwata-san,

Please allow another 24 hours for lab testing.

Best,

David

Hello David-san,

Thank you very much for your support.

Best Regards,
Ishiwata

Hey Shuji,

David has done some bench testing and just needs to write up the response. 

Is this a new design?  The DRV8881 is a very old device, I highly recommend looking at a newer device instead such as DRV8434E.  It is cheaper, higher current, smaller package size.  

Best,

Jacob

Hello David-san,　and Jacob-san,

Thank you very much for your wonderful support.
We will pass this information on to our customers.

The customer is not a new design. I continue to use DRV8881.
Therefore, DRV8434 cannot be used. I would also like to suggest DRV8434 for new designs.

Best Regards,
Ishiwata

Hi Ishiwata-san,

Sounds good!

I will close this post for now but please reach out for any other questions. 

Best,

David