7
Dual Full Bridge Low Voltage Motor Driver
A3901
7
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Functional Description
Device Operation. The A3901 is a dual full-bridge
low voltage motor driver capable of operating one
stepper motor or up to two DC motors. MOSFET
output stages substantially reduce the voltage drop
and the power dissipation of the outputs of the A3901
compared to typical drivers with bipolar transistors.
Internal circuit protection includes thermal shutdown
with hysteresis, clamp diodes, and crossover current
protection.
The A3901 is designed for portable applications with a
power-off (Sleep mode) current of 50 nA typical, and
an operating voltage of 2.5 to 5.5 V. The A3901 logic
inputs are 3 to 5 V logic compatible.
Output current can be regulated by pulse width modu-
lating (PWM) the inputs. The full-bridge outputs
can be paralleled for higher-current applications (see
figure 6).
In conditions where the logic supply voltage drops
below 2.5 V, both the sink and the source R
DS(on)
will
increase beyond the specified values. In extreme cases,
no power will be delivered to the motor(s). However,
the device will not be damaged.
In stepping operation, the device can drive in either
full- or half-step mode. The stepping mode is set by
the signal pattern on the INx terminals, as shown in
the stepping timing diagrams.
External PWM. Pulse width modulating the inputs
allows the output current to be regulated. Slow decay
mode is achieved by holding one input high while
PWMing the other input. Holding one input low and
PWMing the other input results in fast decay. See the
External PWM diagram.
Sleep Mode. Pulling all inputs to 0.5 V or less, sends
the A3901 into Sleep mode, during which it draws
50 nA typical.
Thermal Shutdown. The A3901 will disable the
outputs if the junction temperature reaches 165°C.
When thermal shutdown is entered, after the junction
temperature drops 15°C, the outputs will be re-en-
abled.
Brake Mode. When driving DC motors, the A3901
will go into Brake mode (turn on both sink drivers)
when all inputs, INx, are logic 1. There is no protec-
tion during braking, so care must be taken to ensure
that the peak current during braking does not exceed
the absolute maximum current.
