Dual DMOS Full-Bridge Motor Driver

AMT49702

7

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

FUNCTIONAL DESCRIPTION

Device Operation

The AMT49702 is a dual full-bridge motor driver capable of

operating one stepper motor, two DC motors, or one high-current

DC motor. MOSFET output stages substantially reduce the volt-

age drop and the power dissipation of the AMT49702 outputs,

compared to typical drivers with bipolar transistors.

Output current can be regulated by pulse-width modulating

(PWM) the inputs. In addition to supporting external PWM of

the driver, the AMT49702 limits the peak current by internally

PWMing the source driver when the current in the winding

exceeds the peak current, as determined by a sense resistor. If

internal current limiting is not needed, the sense pin should be

shorted to ground.

Internal circuit protection includes thermal shutdown with hys-

teresis, undervoltage lockout, internal clamp diodes, crossover

current protection, and overcurrent protection.

External PWM

Output current regulation can be achieved by pulse-width modu-

lating the inputs. Slow decay mode is selected by holding one

input high while PWMing the other input. Holding one input low

and PWMing the other input results in fast decay.

Blanking

This function blanks the output of the current sense comparator

when the outputs are switched. The comparator output is blanked

to prevent false overcurrent detections due to reverse recovery

currents of the clamp diodes or to switching transients related to

mately 3 μs.

Sleep Mode

An active-low control input used to minimize power consump-

tion when the AMT49702 is not in use. This disables much of the

internal circuitry including the output drivers, internal regulator,

and charge pump. A logic high allows normal operation. When

coming out of sleep mode, wait 1.5 ms before issuing a command

to allow the internal regulator and charge pump to stabilize.

Enable

When all logic inputs are pulled to logic low, the outputs of the

bridges are disabled. The charge pump and internal circuitry

continue to run when the outputs are disabled.

Thermal Shutdown

The AMT49702 will disable the outputs if the junction tempera-

ture reaches 165°C. When the junction temperature drops 20°C,

the outputs will be enabled.

Brake Mode

When driving DC motors, the AMT49702 goes into brake mode

(turns on both sink drivers) when both of its inputs are high (IN1

and IN2, or IN3 and IN4). There is no current limiting during

braking, so care must be taken to ensure that the peak current dur-

ing braking does not exceed the absolute maximum current.

Internal PWM Current Control

Each full-bridge is controlled by a fixed off-time PWM current

Initially, a diagonal pair of source and sink DMOS outputs are

enabled and current flows through the motor winding and the

equals the internal reference voltage, the current sense compara-

tor resets the PWM latch, which turns off the source driver.

transconductance function:

It is critical to ensure the maximum rating on SENSEx pins

(0.5 V) is not exceeded.

Synchronous Rectification

When a PWM off-cycle is triggered by an internal fixed off-time

cycle, load current recirculates in slow decay SR mode. During

slow decay, current recirculates through the sink-side FET and

the sink-side body diode. The SR feature enables the sink-side

FET, effectively shorting out the body diode. The sink driver is