PBD3517-1 Datasheet, PDF (9/10 Pages) Ericsson – Stepper Motor Drive Circuit

PBD 3517/1
R_Ext
i
R
V_Z
Figure 21. Diode turn-off circuit.
Figure 22. Resistance turn-off circuit.
Figure 23. Zener diode turn-off circuit.
V₁
0V
C_S V₂
Power supply
Figure 24. Power return turn-off circuit.
Figure 25. Power return turn-off circuit for
bilevel .
User Hints
necessary to connect in series with
center tap. This changes the L/R
1. Never disconnect ICs or PC-boards
time constant.
when power is supplied.
5. Never use L_A or L_B for continuous
2. If second supply is not used, discon-
output at high currents. L and L on-
A
B
nect and leave open V , L , L , and
SS A B
RC. Preferably replace the V_MM
time can be altered by changing the
RC net. An alternative is to trigger
supply diodes (D1, D2) with a straight
the mono-flip-flop by taking a STEP
connection.
and then externally pulling the RC
3. Remember that excessive voltages
pin (12) low (0V) for the desired on-
might be generated by the motor,
time.
even though clamping diodes are
used.
4. Choice of motor. Choose a motor
that is rated for the current you need
to establish desired torque. A high
supply voltage will gain better
stepping performance. If the motor is
not specified for the V_MM voltage, a
current limiting resistor will be
6. Avoid V_MM and V_SS power supplies
with serial diodes (without filter
capacitor) and/or common ground
with V_CC. The common place for
ground should be as close as
possible to the IC’s ground pin (pin
3).
7. To change actual motor rotation
direction, exchange motor connec-
tions at P_A1 and P_A2 (or P_B1 and P_B2).
8. Half-stepping. in the half-step mode,
the power input to the motor alter-
nates between one or two phase
windings. In half-step mode, motor
resonances are reduced. In a two-
phase motor, the electrical phase
shift between the windings is 90
degrees. The torque developed is the
vector sum of the two windings
energized. Therefore, when only one
winding is energized, which is the
case in half-step mode for every
second step, the torque of the motor
is reduced by approximately 30%.
This causes a torque ripple.
9. Ramping. Every drive system has
inertia which must be considered in
the drive scheme. The rotor and load
inertia plays a big role at higher
speeds. Unlike the DC motor, the
stepper motor is a synchronous
motor and does not change speed
due to load variations. Examination of
typical stepper motors’ torque versus
speed curves indicates a sharp
torque drop-off for the start-stop
without error curve. The reason for
this is that the torque requirements
increase by the cube of the speed
change. As it can be seen, for good
motor performance, controlled
acceleration and deceleration should
be considered.
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