User Manual

AND8399/D

http://onsemi.com

Timer Overflow ?

Power Up

Initialize microcontroller

Set Coil Current

Set Stepping Mode

Enable Motor Driver

Transparent Mode

Send NXT Pulse

Start Timer

If MSP =

(0 OR 32 OR 64

Delay

Sample SLA−pin

Read Microstep

Position

Figure 24. Sample SLA voltage in Transparent Mode

OR 96)

Stall Detection

The flowchart in Figure 25 gives a simple implementation

of stall detection (based on Figure 24). The sampled SLA

voltage will be compared to a threshold value. If the sampled

SLA voltage is below the threshold, motion will be stopped.

The threshold has to be set in such a way that the sampled

SLA voltage is higher than the threshold when the motor is

free running. If the motor gets blocked, the BEMF will drop

and by this also the SLA voltage resulting in a stall detected.

Motion will be stopped.

Implementing the flowchart as given in Figure 25 will

most probably fail. This because the SLA voltage is already

sampled at the first coil current zero crossing. During start

of the rotation oscillations will be seen in the BEMF

(acceleration of the rotor) and by this also in the SLA

voltage. It’s possible that these oscillations trigger the stall

detection although no stall is present. It’s best to skip the stall

detection for the first full steps. This is however out of the

scope of this document.