3957
FULL-BRIDGE PWM
MICROSTEPPING
MOTOR DRIVER
FUNCTIONAL BLOCK DIAGRAM (A3957SLB shown)
PHASE
10
GROUND
6
7
18
19
UVLO
& TSD
9
15
22
23
VCC
VBB
PFD 2
MIXED-DECAY
COMPARATOR
+
–
BLANKING
VCC
PWM LATCH
R
Q
S
BLANKING
GATE
CURRENT-SENSE
COMPARATOR
+
–
÷3
D/A
+–
RC
5
VTH 3
8 11 13 20
SENSE
17
DISABLE
RS
A3957SA
CT
RT
Dwg. FP-042-1
GROUND 1
D0 2
OUTB 3
LOAD
SUPPLY
4
PFD 5
REF 6
RC 7
GROUND 8
LOGIC
VBB
NC
16
NO
CONNECT
15 SENSE
14 OUTA
13 D 1
12 D 2
11 PHASE
VCC
10
LOGIC
SUPPLY
9 D3
Dwg. PP-056-3
For the ‘A’ package, pins 1 and 8 must
be externally connected together.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Copyright © 1998 Allegro MicroSystems, Inc.