xOUT1

xOUT2

1

2

3

Forward drive

Slow decay

Fast decay

VM

1

2

1

2

3

Reverse drive

Slow decay

Fast decay

xOUT1

xOUT2

3

VM

1

2

3

FORWARD

REVERSE

DRV8843

SLVSAS8A

– APRIL 2011 – REVISED MAY 2011

www.ti.com

Bridge Control

The AIN1 and AIN2 input pins directly control the state of the AOUT1 and AOUT2 outputs; similarly, the BIN1

and BIN2 input pins directly control the state of the BOUT1 and BOUT2 outputs. Either input can also be used

for PWM control of the load. Table 2 shows the logic.

Table 2. H-Bridge Logic

xIN1

xIN2

xOUT1

xOUT2

0

0

Z

Z

0

1

L

H

1

0

H

L

1

1

L

L

The inputs can also be used for PWM control of the motor speed. When controlling a winding with PWM, when

the drive current is interrupted, the inductive nature of the motor requires that the current must continue to flow.

This is called recirculation current. To handle this recirculation current, the H-bridge can operate in two different

states, fast decay or slow decay. In fast decay mode, the H-bridge is disabled and recirculation current flows

through the body diodes; in slow decay, the motor winding is shorted.

To PWM using fast decay, the PWM signal is applied to one xIN pin while the other is held low; to use slow

decay, one xIN pin is held high.

The control inputs have internal pulldown resistors of approximately 100 k

Ω.

Table 3. PWM Function

xIN1

xIN2

FUNCTION

PWM

0

Forward PWM, fast decay

1

PWM

Forward PWM, slow decay

0

PWM

Reverse PWM, fast decay

PWM

1

Reverse PWM, slow decay

The drawings below show the current paths in different drive and decay modes:

Figure 2. Current Paths

8

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