Other Parts Discussed in Thread: DRV8711
Hi all
Would you mind if we ask DRV8889-Q1?
We would like to know the differece of stall detection between DRV8889-Q1's one and DRV8711's one.
We confirmed these using the document slvaei3.(www.ti.com/.../slvaei3.pdf)
<DRV8711's stall detection>
1. Back EMF is only monitored during zero crossing.
2. The measurement window needs to ensure that the coil current has really reached zero. Ringing in the coil voltage waveform around the zero crossing can shorten the measurement window and extra blanking time might be needed.
3. For high motor speeds, this method needs complicated circuitry for fast measurement. So, this method does not work above moderately high motor speeds.
4. This method does not work in Full Step mode - coil current switches between 71% and –71% of full- scale setting in full-step mode; therefore, zero-cross detection is not possible. Some algorithms force a zero-cross period even in full-step mode - but that approach has its own issues.
5. When the motor is spinning slowly, the change in back EMF can be hard to detect.
->We assume that DRV8711 uses this normal Back EMF method. Is it correct?
<DRV8889-Q1's stall detection>
By detecting back-EMF phase shift between rising and falling current quadrants of the motor current, the DRV8889-Q1 device can detect a motor overload stall condition or an end-of-line travel.
For a lightly loaded motor, the TRQ_COUNT is a non-zero value - call it steady count.
As the motor approaches stall condition, TRQ_COUNT approaches zero (call it stall count) and can be used to detect the stall condition.
If at anytime TRQ_COUNT falls below the stall threshold (represented by the 8-bit STALL_TH register), the device will detect stall.
->So, we got that DRV8889-Q1's stall detection uses phase shift between motor current and BEMF.
We would like to know the benefit of DRV8889-Q1's stall deteciton.
We recognize followings;
1. It is possible to use any step mode which includes full step mode.
2. It is possible to detect low power and low speed.
3. Using TORQUE_COUNT, it is possible to show the stall condition clearly.Especially, it shows motor load and starting of stall.
Is our recognition correct?
Kind regards,
Hirotaka Matsumoto
