Dual DMOS Full-Bridge

Microstepping PWM Motor Driver

A3973

6

Allegro MicroSystems, Inc.

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Serial Interface.

The A3973SB/SLB is controlled via a

3-wire (clock, data, strobe) serial port. The programmable func-

tions allow maximum flexibility in configuring the PWM to the

motor drive requirements. The serial data is written as two

19-bit words: 1 bit to select the word and 18 bits of data. The

serial data is clocked in starting with D18.

Word 0 Bit Assignments

Bit

Function

D0

Word select = 0

D1

Bridge 1, DAC, LSB

D2

Bridge 1, DAC, bit 2

D3

Bridge 1, DAC, bit 3

D4

Bridge 1, DAC, bit 4

D5

Bridge 1, DAC, bit 5

D6

Bridge 1, DAC, MSB

D7

Bridge 2, DAC, LSB

D8

Bridge 2, DAC, bit 2

D9

Bridge 2, DAC, bit 3

D10

Bridge 2, DAC, bit 4

D11

Bridge 2, DAC, bit 5

D12

Bridge 2, DAC, MSB

D13

Bridge 1 phase

D14

Bridge 2 phase

D15

Bridge 1 mode

D16

Bridge 2 mode

D17

REF select

D18

Range select

D1 – D6 Bridge 1 Linear DAC.

Six-bit word sets desired

current level for Bridge 1. Setting all six bits to zero disables

Bridge 1, with all drivers off (See current regulation section of

functional description).

D7 – D12 Bridge 2 Linear DAC.

Six-bit word sets desired

current level for Bridge 2. Setting all six bits to zero disables

Bridge 2, with all drivers off (See current regulation section of

functional description).

FUNCTIONAL DESCRIPTION

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D13 Bridge 1 Phase.

This bit controls the direction of output

current for Load 1.

D13

0

L

H

1

H

L

D14 Bridge 2 Phase.

This bit controls the direction of output

current for Load 2.

D14

0

L

H

1

H

L

D15 Bridge 1 Mode.

D15

Mode

0

Mixed-decay

1

Slow-decay

D16 Bridge 2 Mode.

D16

Mode

0

Mixed-decay

1

Slow-decay

D17 REF Select.

This bit determines the reference input for

the 6-bit linear DACs.

D17

Reference Voltage

0

Internal 2 V

1

External (3 V max)

(4 or 8) used.

D18

Divider

Load Current

0

1/8

1

1/4