DRV8889-Q1EVM: Stall detection

Hey Yuki,

You can monitor the TRQ_COUNT bit, see 7.3.11.5 Stall Detection in the datasheet for more explanation.

"The algorithm compares the back-EMF between the rising and falling current quadrants by monitoring PWM off time and generates a value represented by the 8-bit register TRQ_COUNT. The comparison is done in such a way that the TRQ_COUNT value is practically independent of motor current, motor winding resistance, ambient temperature and supply voltage."

For a "waveform" you can probe the Torque Count pin on the EVM, the MCU on the EVM reads the value of the TRQ_COUNT register and uses a DAC to put this on the test point as an analog voltage I believe.  Check the EVM user guide for more info on that conversion. 

Here's our app note with a lot more information about stall detection with this device: Sensorless Stall Detection With the DRV8889-Q1

Best,

Jacob

Hi Jacob.
My understanding is that the torque count pin converts the internally calculated torque count value into voltage by DAQ and outputs it.
Is it possible to visualize or numerically observe reverse electromotive voltage and Toff(PWM?) in waveforms?

Hey Yuki,

Correct, but it is the MSP430 MCU on the EVM that is doing that after each SPI read.  The DRV8889 does not have a Torque Count output pin itself.

You can do the same thing with your microcontroller if you externally control and communicate with the DRV8889.  Just read the SPI register and then use a DAC to output the waveform of what you want.  

The firmware for the EVM is available online on the EVM page under software downloads, you could modify that to output something different than torque count.  

Best,

Jacob