DRV8701: Reverse Direction performance

Eugene Estok

Part Number: DRV8701

I am using the DRV8701E motor controller to drive a brushed 24VDC motor. The circuit design is the same as the full bridge circuit referenced in the data sheet. We have been using this design in our application for a year without any issues. We now seem to be experiencing behavior where the reverse drive direction is performing poorly compared to the forward drive direction (as if we were using the DRV8701P by mistake). We eliminated the possibility of the load being different. Any suggestions on performance with regards to direction?

over 5 years ago

0 Rick Duncan over 5 years ago

TI__Guru** 114905 points

Hi Eugene,

How many devices show this behavior? How many devices do not?

Can you provide:

Scope captures of the inputs (PH/EN) and outputs (SH1 and SH2) in both directions?
A snippet of the schematic showing the components connected to the DRV8701?

The markings on the top of the device (or a photo showing the markings)?

0 Eugene Estok over 5 years ago in reply to Rick Duncan

Prodigy 65 points

Rick,

Let me first mention that the only way I was able to match forward and reverse performance was to remove all current regulation, as per the data sheet.

We were hoping to use the SO output to monitor pump current

With the following tests/images, I set the EN pin to 5V (No PWM) and the PH pin to either 0V or 5V. (Note that current regulation is enabled).

With PH=0V, Gate drives are full ON. With PH=1, Gate drives are PWM.

(Attached word doc with requested captures)

1780.Motor.docx

0 Hector Hernandez Luque over 5 years ago in reply to Eugene Estok

TI__Expert 8985 points

Hi Eugene,

Can you provide the layout of this design?

If it needs to be shared privately, I have opened communication to do so.

0 Eugene Estok over 5 years ago in reply to Hector Hernandez Luque

Prodigy 65 points

Do you have a preferred format? Can provide Altium Designer PCB or gerber data.

0 Hector Hernandez Luque over 5 years ago in reply to Eugene Estok

TI__Expert 8985 points

Hi Eugene,

Altium is perfect. Thank you.

0 Eugene Estok over 5 years ago in reply to Hector Hernandez Luque

Prodigy 65 points

PCB File attached. I can provide project files if needed. Also note that the previous revision of the board did not exhibit this behavior.

Marking on motor Driver:

8701E

TI 7AI

CL 7DXFLO_MAIN_PCB_REV_6.zip

0 Hector Hernandez Luque over 5 years ago in reply to Eugene Estok

TI__Expert 8985 points

Hi Eugene,

Please share the current project files if possible.

Can you indicate the differences between the current board and this board? If you need to share the previous design files, I am willing to do a comparative analysis.

0 Eugene Estok over 5 years ago in reply to Hector Hernandez Luque

Prodigy 65 points

Hector,

The circuit for the motor driver circuit did not change "schematically" but the layout changed.

I have attached the previous rev PCB.

XFLO_MAIN_Rev_5.zip

Gene

0 Hector Hernandez Luque over 5 years ago in reply to Eugene Estok

TI__Expert 8985 points

Hi Eugene,

Q5's SP trace has a larger voltage delta than Q6's SP trace to the sense resistor. Both pin traces need to have a common point, the SP node of the sense resistor before they come back to the DRVs SP pin. Please, see section 7 Current Sense Amplifier Routing of the following doc for more information

http://www.ti.com/lit/an/slva959a/slva959a.pdf

I recommend you do that change and also, please review the document above before your next revision to follow our best practices.

Let me know if you have any questions.

0 Hector Hernandez Luque over 5 years ago in reply to Hector Hernandez Luque

TI__Expert 8985 points

Hi Eugene,

The previous layout is actually a great example of how to layout SP as well as SN. Also, consider the trace width to be 20mil.

I will suggest you use that layout as a great example.

0 Eugene Estok over 5 years ago in reply to Hector Hernandez Luque

Prodigy 65 points

Thanks Hector,

I noticed the newer rev being less than ideal. I reworked the circuit to comply with recommendations and the motor worked perfectly.

Gene

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DRV8701: Reverse Direction performance