DRV8462: Stepper motor driving cannot be performed under high frequency pulses

Hi Annie,

This is typical behavior of the stepper motors. You can also refer to the speed vs. torque plots from the motor vendor. Torque reduces rapidly at higher speeds and the motor will not run but will generate audible noise. This is because at higher step rates the VM will not be sufficient to overcome the BEMF and push the current through the motor coils. I think you had a similar question about 3-months ago. See these E2E.

1. https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1307969/drv8462-it-can-drive-the-motor-at-low-frequency-but-cannot-make-the-motor-run-at-high-frequency?tisearch=e2e-sitesearch&keymatch=drv8462# 

2. https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1272947/drv8462-loses-step-and-stalls-in-proximity-to-the-stepper-motor 

3. https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1286472/drv8462-achieving-a-current-sine-wave-approaching-2000rpm/4902252?tisearch=e2e-sitesearch&keymatch=drv8462#4902252 

Regards, Murugavel

Hi Murugavel,

The customer's understanding is that when the motor is no-load, the torque demand should not be large. The same motor can achieve higher speeds using another driver chip. Isn't it possible that DRV8462 can drive this motor above 300rpm?

The relationship between motor torque and speed is as follows:

Regards,

Annie

Hi Annie,

"The same motor can achieve higher speeds using another driver chip. Isn't it possible that DRV8462 can drive this motor above 300rpm?". Under the same conditions another chip and DRV8462 should behave in a similar fashion. What is the VM, IFS and microstep setting and what current decay mode is used? 

Can we get the stepper current waveform at 300rpm from both DRV8462 and another driver chip for comparison? Thanks.

Regards, Murugavel 

Hi Murugavel,

The customer uses Oriental Motor's driver and AMi's tmc5240 chip. This model also has a 24V voltage, a maximum operating current of 2.02A, and a microstep setting of 256 subdivisions. It can already drive a motor with the same load at high frequency.

Customers are temporarily unable to capture the current waveform generated by the 8462 chip, but another chip can. 

With 128 subdivisions and a speed setting of 300rpm, the drv8462 chip itself is easily protected from overheating, and adding a heat sink cannot avoid this problem. What could be the cause?

Regards,

Annie

Hi Annie,

Can we get the datasheet of the stepper motor used? If I have a similar motor with us I can try it with a DRV8462EVM with 24V and 2A current setting with 256 uSteps.

"Customers are temporarily unable to capture the current waveform generated by the 8462 chip, but another chip can. ". Can you share the other chip's waveform for now and share DRV8462 waveform as soon as the customer captures it.

"With 128 subdivisions and a speed setting of 300rpm, the drv8462 chip itself is easily protected from overheating, and adding a heat sink cannot avoid this problem. What could be the cause?". I am unable to understand this statement. Does it mean with 128 uSteps DRv8462 was able to perform 300RPM without overheating and with 256 uSteps 300RPM DRV8462 was having a OTSD? thermal shutdown. 

With the DRV8462 how did the customer run the stepper at 300RPM with 256 uSteps? Did they use auto microstepping? What was the STEP input frequency used? 

Regards, Murugavel 

Hi Murugavel,

In HW mode, adjust the voltage of VREF to 3.3V. When the subdivision 128ustep runs the motor at a speed exceeding 300rpm, the chip will quickly overheat for protection. When automatic micro-stepping is not turned on and there is no silent current saving, setting the maximum operating current to 0xB0, VREF2.2V, and running at 300rpm in SPI mode will prevent overheating. But the situation is the same when VREF is 3.3V. 

The stepper motor model is Lesai Motor 60CME22X. 雷赛闭环刹车电机60CME22X-BZ 60CME30X-BZ1.5M线加点可开13%增票 (1688.com)

Customer does not have the tool to capture the DRV8462 waveform. The current waveform of another chip when running above 300rpm is as follows:

Regards,

Annie

Hi Annie,

Thanks for the additional details. In HW mode when VREF = 3.3V the IFS current will be set to 5A. This is the maximum current rating of the DRV8462 and resulting in high power dissipation. If the customer wants to use IFS 5A with 24V they should consider the DRV8462 in DDV package with external heatsink.

The below snapshot shows the customer's stepper motor specifications. Note, the current rating per phase is 5A. So the DRV8462 DDV can generate maximum torque output from the motor while supporting 5A continuous without overtemperature issues.

The screen capture from competition is not the current waveform but has the current value I was looking for. The competition chip supports only up to 3A peak and up to 2A continuous coil current. So the customer test with VREF = 3.3V was not apples-to-apples comparison done by the customer. 

Based on the screen capture you shared the current setting in the competition setup used by the customer was 2.121A. For this current in the DRV8462 HW mode the VREF must be set to VREF = Kv * IFS = 0.66 * 2.121 = 1.4V. The DRV8462 in DDW should be able to support much higher current than the competition 2.12A without over temperature.

I have a similar motor with me and tested with the DRV8462EVM in HW mode. I was able to get over temperature protection with VREF = 3.3V or 5A with 24V drive as expected. If I reduced the VM to 12V then the DRV8462 support this 5A, however the device temperature was around 130C with Ta = 25C. Like I mentioned before 24V and 5A will be a non-issue with the DDV package. 

Now after setting VREF = 1.4V the DRV8462 ran the stepper with no over temperature protection kicking in. The device temperature was 106C with Ta = 25C. The Rdson of the DRV8462 is 100mΩ whereas the TMC5240 is 230mΩ which is 2.3x higher resistance than the DRV8462. So for 2.121A it will run hotter than the DRV8462.

I did additional tests with higher currents than the competition device can support. 24V with IFS = 3A, the DRV8462 had no issues supporting this current. The device temperature at Ta = 25C was 132C. The DRV8462 drove the motor for long periods of time with no over temperature. This is a safe drive level for an application.

24V with IFS = 4A, the DRV8462 had no issues supporting this current. The device temperature at Ta = 25C was 152C. The DRV8462 drove the motor for long periods of time with no over temperature. Note, this is at the top end of the operating temperature and not recommended in an application. 

Conclusion: The DRV8462 supported IFS = 4A with 24V with no thermal overcurrent. The competition device can support only up to 3A peak and 2A continuous according to its datasheet. The customer was testing it at 2.121A. The customer was testing DRV8462 in HW mode with IFS = 5A ad 24V VM and encountered thermal protection which is expected behavior. 

Regards, Murugavel

Hi Murugavel,

Lowering the IFS and Vref voltages can indeed lower the chip temperature without overheating under motor rotation. But after setting Vref=1.4V, the motor cannot move at 300rpm. There was a situation where it was stuck by the reverse electromotive force before. What is the range of segmentation and frequency settings you set during testing?

Regards,

Annie

Hi Annie,

Perhaps the customer may have to try a different current decay mode setting such as the Smart Tune dynamic decay instead of the default STRC. This also should be matched between competition and TI. How did the customer run the DRV8462 at 300RPM and 256microstepping? What was the input STEP frequency?

I ran the stepper motor with 300RPM speed. Both with STRC decay and STDD decay settings. STDD decay settings torque output was lot better. 

If the customer still experiences issues, the best way to debug this issue would be to capture the current waveforms from the two drivers under the same settings. Thanks.

Regards, Murugavel

Hi Murugavel,

In SPI mode, intelligent tuning dynamic attenuation and static power saving mode are adopted. Driving the motor at 300rpm at 64 divisions will no longer overheat. May I know how to lock the motor in static power-saving mode and prevent it from being rotated manually? Is it by adjusting the holding current value? Currently, in the stationary power-saving mode, the motor shaft can be manually rotated.

What is the highest precision that can be achieved for the DRV8462 drive motor? Can it support a driving capability with a resolution of 1um accuracy?

Regards,

Annie

Hi Annie,

With standstill power saving mode the HOLD current can be configured in a register between 1% and 100% of the IFS. Customer can choose a suitable value of the hold current that will provide the required hold torque without overheating the motor at standstill.

The DRV8462 supports up to 256 microsteps. It depends on the customer's mechanical design and system accuracy including backlash whether they can achieve 1um resolution or not. 

Regards, Murugavel

Reduce the operating current to a safe level that the motor and the DRV8462 can handle without overheating.Consider adding subdivision to improve microstepping resolution, which can enhance motor smoothness and reduce audible noise. provide proper cooling for the DRV8462. You can see this motor driver board for your reference.

www.pcbway.com/.../ESP_12F_DRV88xx_Motor_Driver_Development_Board_bc4e7391.html

This is a  DRV8848 Motor Driver Development Board, not DRV8462. But  this may give some guideline. 

Hi,

Thank you for your questions. Friday is national holiday in US. Our expert will reply to you when back to office.

regards

Shinya