AMIS-30621 LIN Micro-stepping Motor Driver
Data Sheet
output current to an internal reference, and features a digital regulation generating the PWM signal that drives the output switches. The
zoom over one micro-step in the Figure 21 shows how the PWM circuit performs this regulation.
14.3.3. Motor Starting Phase
At motion start, the currents in the coils are directly switched from Iholdto Irunwith a new sine/cosine ratio corresponding to the first
half (or micro) step of the motion.
14.3.4. Motor Stopping Phase
At the end of the deceleration phase, the currents are maintained in the coils at their actual DC level (hence keeping the sine/cosine
ratio between coils) during the stabilization time tstab equal to 1/4th of an electrical period at the Vminvelocity. The currents are then set
to the hold values, respectively Iholdx sin(TagPos)and Iholdx cos(TagPos) as illustrated below. A new positioning order can then
be executed.
Ix
Iy
t
tstab
PC20070303.6
Figure 21: Motor Stopping Phase
14.3.5. Charge Pump Monitoring
If the charge pump voltage is not sufficient for driving the high side transistors (due to a failure), an internal HardStop command is
issued. This is acknowledged to the master by raising flag <CPFail> (available with command GetFullStatus). In case this failure
occurs while a motion is ongoing, the flag <StepLoss> is also raised.
14.3.6. Electrical Defect on Coils, Detection and Confirmation
The principle relies on the detection of a voltage drop on at least one transistor of the H-bridge. Then the decision is taken to open the
transistors of the defective bridge. This allows detecting the following short circuits:
• External coil short circuit
• Short between one terminal of the coil and Vbat or Gnd
• One cannot detect internal short in the motor
Open circuits are detected by 100 percent PWM duty cycle value during a long time.
AMI Semiconductor – Sept. 2007, Rev 1.5
33
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