Brushed DC Motor Driver IC With PWM Control

STA6940M

6

Basic Motor Control Functions

There are four states of motor output: free (coast), forward,

reverse, and brake. This section describes the inputs and the

MOSFET outputs that set these states.

Free (Coast)

This state is set by low signals on both the IN1 and

the IN2 logic inputs. All MOSFETs are turned off, and no current

flows through the device to the motor. The motor is totally free to

spin. The MOSFET states are shown in figure 1(A).

Forward

This state is set by a high signal on the IN1 input and

a low signal on the IN2 input. The high-side MOSFET on the

OA side is turned on, and the low-side MOSFET on the OB side

is turned on. Current flows through the device to drive motor

rotation (the terms "forward" and "reverse" only serve to indicate

opposite relative directions). The MOSFET states are shown in

figure 1(B).

Reverse

This state is set by a low signal on the IN1 input and a

high signal on the IN2 input. The low-side MOSFET on the OA

side is turned on, and the high-side MOSFET on the OB side is

turned on. Current flows through the device to drive motor rota-

tion (the terms "forward" and "reverse" only serve to indicate

opposite relative directions). The MOSFET states are shown in

figure 1(C).

Brake

This state is set by high signals on both the IN1 and the

IN2 logic inputs. Both high-side MOSFETs are turned off, and

both low-side MOSFETs are turned on. The motor coils are

shorted together providing resistance to rotation. The MOSFET

states are shown in figure 1(D).

Motor

VM

OA

OB

OFF

OFF

OFF

OFF

Rs

Motor

VM

OA

OB

ON

OFF

OFF

ON

IM

Rs

Motor

VM

OA

OB

OFF

ON

ON

OFF

IM

Rs

Motor

VM

OA

OB

OFF

OFF

ON

ON

Rs

Figure 1. The panels demonstrate the MOSFET switching

conditions and the resulting current flow for each of the

four motor control states.

(A) Free (coast)

(B) Forward

(C) Reverse

(D) Brake

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com