DRV8889-Q1: Stall detection issues

Hi Daniel,

The register configurations look like they are set up properly for stall detection. 

What type of motor are you using (winding resistance, torque rating)?

What's the step rate?

Please see the following FAQ on some common issues that can cause unreliable stall detection:

(+) [FAQ] How to troubleshoot common Stepper Stall Detect Issues - Motor drivers forum - Motor drivers - TI E2E support forums 

Best,

David

Hello Medis,

Thanks for sharing.

Pls see the customer check result according to link:

1. Stall Detection function requires Smart Tune Ripple Control decay mode. This is the default decay mode of the devices with Stall Detection feature.

Answer: I have configured it to ‘Smart Tune Ripple Control decay mode’, CTRL1 [bit0:2]=111b;

1. In order for the stall detection to work properly not only the STALL THRESHOLD value must be defined correctly but also the back emf amplitude should satisfy the SNR required by the stall detector to compute the TORQUE COUNT The higher the phase winding resistance of the stepper motor, the lower the amplitude of the back emf. Hence stepper motors with high winding resistance of the order of several 10’s of ohms may not work well with the stall detector.

Answer: The motor coil resistance is about 8.2Ω. Stall threshold is 100;

1. Small form factor and/or low torque stepper motors likely have weak permanent magnets and may not provide enough SNR with the back emf generated and may not work well with the stall detector.

Answer: Motor parameters are shown in here: PL35L-A24_zh.pdf (minebeamitsumi.com.cn), motor is same as TI document “Sensorless Stall Detection With the DRV8889-Q1”.

1. At very low step rates the back emf amplitude may not be high enough to be in the detectable range of the stall detector. Stall detection may not work well at low step rates. The lowest step rate usable for stall detection can be determined by evaluating different motors at various VM and current settings using a device specific TI EVM.

Answer:

1. Previously learned STALL THRESHOLD values at one speed may NOT be suitable to detect stall at another speed. A new learning procedure must be done every time stepper speed is changed.

Answer: I didn’t use stall learn mode, filled a const value(100) in CTRL6.

1. Similarly, manually input STALL THRESHOLD value at one speed may not be suitable to detect stall at another speed. A new STALL THRESHOLD value must be input every time stepper speed is changed.

Answer: In general, 100 is bigger than TRQ_COUNT, at least in my case.

1. Stall detection using STALL THRESHOLD learning may not be reliable during acceleration phase if implemented in an application. In such scenario an appropriate STALL THRESHOLD value must be manually set.

Answer: Yes, I manually set it.

1. TORQUE COUNT computation for stall detection relies on observing finite TOFF duration during every current regulation chopper cycle. If the motor drive supply voltage VM is not sufficient to push enough current through the phase winding inductance to sustain regulation at a given stepping rate, not only the current regulation will be lost but also the stall detection will not work. A sudden jump in the TORQUE COUNT value to an unusually higher value while the stepping speed is increased suggests both loss of current regulation and loss of stall detection capability at that speed. The motor may or may not stall when current regulation is lost depending on the inertia and the acceleration profile of the system.

Answer: VM is 13V, coil current is 500mA, wave is as picture.

Can you help share your insights for the issue?

Hi Daniel,

The DRV8889-Q1 is known to work well with PL35L stepper actuator for stall detection and currently in production for headlight level control application for a while now. The stall threshold value of 100 mentioned by you seems a bit high. 

Was it 1/16 uSteps? Did you also try 1/8 uSteps setting? What was the torque count with no stall and count during stall, what was the PPS step input? Thank you.

Regards, Murugavel 

Hello Murugavel,

Now it is 1/8 step. TRQ_Count is about 100-120 without stall, 0-10 with stall. PPS I am not sure, I can show you my config:

Thanks!

Hi Daniel,

In this scenario a stall threshold of 40 to 50 should be able to detect a stall condition consistently. Thanks.

Regards, Murugavel