AMIS-30622_13 Datasheet, PDF (33/50 Pages) ON Semiconductor – I2C Micro-Stepping Motor Driver

AMIS−30622
Motor Starting Phase
At motion start, the currents in the coils are directly
switched from <Ihold> to <Irun> with a new
sine/cosine ratio corresponding to the first half (or micro−)
step of the motion.
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 t_stab (see AC Table). The currents are then
set to the hold values, respectively Ihold x sin(TagPos)
and Ihold x cos(TagPos), as illustrated below. A new
positioning order can then be executed.
Iy
Ix
t
Figure 20. Motor Stopping Phase
t _stab
Charge Pump Monitoring
If the charge pump voltage is not sufficient for driving the
high side transistors (due to failure), an internal HardStop
command is issued. This is acknowledged to the master by
raising flag <CPFail> (available with command
GetFullStatus1).
In case this failure occurs while a motion is ongoing, the
flag <StepLoss> is also raised.
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 the detection the following short circuits:
• External coil short circuit
• Short between one terminal of the coil and Vbat or GND
One cannot detect an internal short in the motor.
Open circuits are detected by 100% PWM duty cycle
value during one electrical period with duration, determined
by Vmin.
Table 22. ELECTRICAL DEFECT DETECTION
Pins
Fault Mode
Yi or Xi
Short−circuit to GND
Yi or Xi
Short−circuit to Vbat
Yi or Xi
Open
Y1 and Y2
Short circuited
X1 and X2
Short circuited
Xi and Yi
Short circuited
Motor Shutdown Mode
A motor shutdown occurs when:
• The chip temperature rises above the thermal shutdown
threshold Ttsd (see Thermal Shutdown Mode).
• The battery voltage goes below UV2 for longer than 15
seconds (see Battery Voltage Management).
• The charge pump voltage goes below the charge pump
comparator level for more than 15 seconds.
• Flag <ElDef> = ‘1’, meaning an electrical problem is
detected on one or both coils, e.g. a short circuit.
A motor shutdown leads to the following:
• H−bridges in high impedance mode.
• The <TagPos> register is loaded with the <ActPos>,
except in autarkic states.
The conditions to get out of a motor shutdown mode are:
• Reception of a GetFullStatus1 command AND
• The four above causes are no longer detected
This leads to H−bridges going in Ihold mode. Hence, the
circuit is ready to execute any positioning command.
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