DRV8711: DRV8711DPC FAULT PIN ENABLE

Hi,

Have you tried reading the SPI registers to see what type of fault is occurring? 

Do you think you can share with me your schematic?

Hi,

     The register shows over current error. Below are the schematics. DRV8711 DRIVER REV3.pdfDRV8711 DRIVER REV4.pdf

Hi,

Thank you for sending the schematic. I have a couple questions.

• Are you seeing the OCP fault being triggered on all four IC's or just on certain ones?
• Can you send me your SPI register settings?

Hi,

     All 4 motors occurs fault signal. Motor1>>5%, Motor2>>10 %, Motor3>>25%, Motor4>>>60%. Below are the motor spec:

Motor 1: 2.4VDC, 2A/PHASE, 1.2ohm

Motor2,3,4:2.6VDC, 4A/PHASE, 0.65ohm, 2.4mH

CTRL Resister: 0x0C34

TORQUE Resister: 0x07FF

OFF Resister: 0x0030

BLANK Resister: 0x00FF

Decay Resister: 0x0410

STALL Resister: 0x0040

 DRIVE Resister: 0x006A

Regards

Jason

Hi Jason,

Pablo is not available today, so I am responding for him. Thank you for the additional information.

There are a few register settings to address.

First, please change the DECAY register to either 0x0510 (auto mixed decay) or 0x0310 (mixed decay) as a starting point.

Then please change the BLANK register to 0x0180 (adaptive blanking and 2us TBLANK)

The TORQUE register should be set to either 0x075D (.05Ohm resistor) or 0x0782 (.07 Ohm resistor). This should limit the current to 4A full scale

These changes should help get you closer to your goal and hopefully remove the overcurrent faults. The overcurrent faults were probably due to a combination of setting the TBLANK too long and the TOFF too short.

For more information, please see the Decay Mode Setting Optimization  and DRV8711 Quick Spin and Tuning Guide www.ti.com/.../SLVA632

Hi  Rick,

               Thank you for your reply. I will let our engineer to do more test when change the register. And we also notice a interesting thing. We change the MOSFET CSD88539ND to CSD88537ND. Suddenly the issue are solved without adjusting the register setting. Do you think any possibility the issue comes  from the MOSFET? And do TI have the recommended MOSFET list or how can we to select a suitable one? Thank you for your support.

Jason

Hi Rick,

             We tried to adjust the register you told us. But it's the same result. Is there any other solution?

Regards

Jason 

Hi Jason,

Do you have a current probe? If so, please provide a scope capture of the current through the windings just prior to the nFAULT signal asserting.

This will help provide information on the cause.

If you do not have a current probe, please provide a scope capture of the voltage across the sense resistor to GND prior to nFAULT asserting. This can be more difficult to interpret.

Has the firmware engineer confirmed the registers writes?

If the motor is not connected, do you get the OCP fault? If so, please check the layout.

Hi Jason,

Do you have any updates?

Hi Rick,

              Please refer to the attached file.

DRV8711 MOTOR CURRENT MEASUREMENT.pdfDRV8711 SHUNT RESISTOR VOLTAGE MEASUREMENT.pdf

Jason

Hi Jason,

If you still have problem there are some my suggestions

1. Use gate resistor (47 - 100 Ohm) for low side MOSFETS

2. Try to eliminate RC filters for AISENN/AISENP (differential pair from sense resistor to AISENN/AISENP placed over PCB ground layer could be sufficient) 

Less important:

3. Instead of polymer caps decoupling 24V, better choice might be 10-100nF MLCC for each high side MOSFET (placed as close as possible to these mosfets and GND) + 1uF- 2,2uF MLCC for each

H-bridge + single 1000uF - 4700 uF electrolytic cap to store energy from vibrations and breaking.

4. Use 4 layer PCB with 1-2 ground layers if possible.

5. 0,022 - 0,033 Ohm resistor might be a better choice for 4A (less power losses and still good current control)

Grzegorz

Hi Jason,

Do you have a current probe? If so, please provide a scope capture of the current through the windings just prior to the nFAULT signal asserting.

This will help provide information on the cause.

If you do not have a current probe, please provide a scope capture of the voltage across the sense resistor to GND prior to nFAULT asserting. This can be more difficult to interpret.

Thank you for the scope captures. Can you answer a few questions about them?

1) What is the scale in the current captures? 10mV = ?A
2) Is the motor accelerating (STEP frequency increasing) in the PHASE A and PHASE B image?
        What is the STEP frequency range?
3) When did the fault occur in 2. Motor Current Waveform (Fault pin enabled)
4) What fault was reported by the DRV8711?
5) What is the STEP frequency in Image 1 of the shunt resistor images?

Has the firmware engineer confirmed the registers writes?

If the motor is not connected, do you get the OCP fault? If so, please check the layout.

Hi Rick,

             I need more time to do test. Will update later. Thank you for your support.

Jason

Hi Jason,

Thank you for the update. For now we will close the thread.

Please reply to it when you have an update. If the thread is locked, please select "Ask a related question" at the top of the thread.