3973
DUAL DMOS FULL-BRIDGE
MICROSTEPPING PWM MOTOR DRIVER
FUNCTIONAL DESCRIPTION
Serial Interface.
The A3973SB/SLB is controlled via a
3-wire (clock, data, strobe) serial port. The programmable
functions 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
D0
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D12
D13
D14
D15
D16
D17
D18
Function
Word select = 0
Bridge 1, DAC, LSB
Bridge 1, DAC, bit 2
Bridge 1, DAC, bit 3
Bridge 1, DAC, bit 4
Bridge 1, DAC, bit 5
Bridge 1, DAC, MSB
Bridge 2, DAC, LSB
Bridge 2, DAC, bit 2
Bridge 2, DAC, bit 3
Bridge 2, DAC, bit 4
Bridge 2, DAC, bit 5
Bridge 2, DAC, MSB
Bridge 1 phase
Bridge 2 phase
Bridge 1 mode
Bridge 2 mode
REF select
Range select
D13 Bridge 1 Phase.
This bit controls the direction of
output current for Load 1.
D13
OUT
1A
OUT
1B
0
1
L
H
H
L
D14 Bridge 2 Phase.
This bit controls the direction of
output current for Load 2.
OUT
2B
D14
OUT
2A
0
1
D15 Bridge 1 Mode.
D15
0
1
D16 Bridge 2 Mode.
D16
0
1
Mode
Mixed-decay
Slow-decay
Mode
Mixed-decay
Slow-decay
L
H
H
L
D17 REF Select.
This bit determines the reference input for
the 6-bit linear DACs.
D17
0
1
Reference Voltage
Internal 2 V
External (3 V max)
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).
D18 G
m
Range Select.
This bit determines the scaling factor
(4 or 8) used.
D18
0
1
Divider
1/8
1/4
Load Current
I
TRIP
= V
DAC
/8R
S
I
TRIP
= V
DAC
/4R
S
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