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

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.