Automotive Full Bridge MOSFET Driver

A3941

9

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Table 1. Phase Control Truth Table

Inputs

Outputs

Bridge

Mode of Operation

PWMH

PWML

PHASE

SR

GHA GLA GHB GLB

SA

SB

1

1

1

X

H

L

L

H

HS

LS

Bridge driven with A high and B low

1

1

0

X

L

H

H

L

LS

HS

Bridge driven with B high and A low

0

1

X

1

L

H

L

H

LS

LS

Slow decay, both low-side on or low-side brake

1

0

X

1

H

L

H

L

HS

HS

Slow decay, both high-side on or high-side brake

0

1

1

0

L

L

L

H

Z

LS

Slow decay, current flow A to B, low-side diode rectification

0

1

0

0

L

H

L

L

LS

Z

Slow decay, current flow B to A, low-side diode rectification

1

0

1

0

H

L

L

L

HS

Z

Slow decay, current flow A to B, high-side diode rectification

1

0

0

0

L

L

H

L

Z

HS

Slow decay, current flow B to A, high-side diode rectification

0

0

X

X

LLLL

Z

Z

Fast decay, diode rectification/coast

X = don’t care (same for input 1 or input 0), HS = high-side FET active, LS = low-side FET active, Z = high impedance, both FETs off

Table 2. PWM Options

Decay

Mode of Operation

SR

PWMH

PWML

PHASE

100%

0%

X

1

1

PWM

A to B

B to A

Fast

Full four-quadrant control, zero average load current at 50% PWM

0

PWM

PWM

1

A to B

Coast

Fast

Fast decay, diode recirculation or coast

0

B to A

1

PWM

1

1

A to B

Brake

Slow

High-side PWM, low-side MOSFET recirculation

0

B to A

1

1

PWM

1

A to B

Brake

Slow

Low-side PWM, high-side MOSFET recirculation

0

B to A

0

PWM

1

1

A to B

Slow

High-side PWM, low-side diode recirculation

0

B to A

0

1

PWM

1

A to B

Slow

Low-side PWM, high-side diode recirculation

0

B to A

X

0

0

X

Coast

Coast

Fast

Coast, all MOSFETs off