
January 2013L010132
Step Motor Confi gurations
The output current on the MBC25081 is set by the onboard potentiometer. This potentiometer determines
the per phase peak output current of the driver. The relationship between the output current and the po-
tentiometer value is as follows:
WARNING! Step motors will run hot even when confi gured correctly. Damage may occur to the motor if
a higher than specifi ed current is used. Most specifi ed motor currents are maximum values. Care should
be taken to not exceed these ratings.
MBC25081 Potentiometer Settings
Peak
Current
Potentiometer
Setting
Peak
Current
Potentiometer
Setting
0.50A 0% 1.70A 60%
0.70A 10% 1.90A 70%
0.90A 20% 2.10A 80%
1.10A 30% 2.30A 90%
1.30A 40% 2.50A 100%
1.50A 50% -- --
Reducing Output Current
Reducing the output current is accomplished automatically and occurs approximately 20mSec after the
last of the clock input has been received. The amount of current per phase in the reduction mode is ap-
proximately 70% of the set current. When the current reduction circuit is activated, the current reduction
resistor is paralleled with the current adjustment potentiometer. This lowers the total resistance value,
and thus lowers the per phase output current.
Connecting the Step Motor
Phase 1 and Phase 3 of the step motor are connected to pins 1 and 2 on connector P2. Phase 2 and
Phase 4 of the step motor are connected to pins 3 and 4 on connector P2. Please refer to the fi gure for
a typical APPLICATION HOOK-UP.
Note: the physical direction of the motor with respect to the direction input will depend on the connection
of the motor windings. To reverse the direction of the motor with respect to the direction input, switch the
wires on Phase 1 and Phase 3.
WARNING: DO NOT CONNECT OR DISCONNECT MOTOR WIRES WHILE POWER IS APPLIED!
Motor Selection
The MBC25081 is a Bipolar Microstep Driver that is compatible with both Bipolar and Unipolar Motor
Confi gurations, (i.e. 8 and 4 lead motors, and 6 lead center tapped motors).
Step motors with low current ratings and high inductance will perform better at low speeds, providing
higher low-end torque. Motors with high current ratings and low inductance will perform better at higher
speeds, providing more high-end torque.
Since the MBC25081 uses a constant current source drive technique, it is not necessary to use a motor
that is rated at the same voltage as the supply voltage. What is important is that the potentiometer is set
to the appropriate current level based on the motor being used. Higher voltages will cause the current to
fl ow faster through the motor coils. This in turn means higher step rates can be achieved. Care should
be taken not exceed the maximum voltage of the driver.
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