26184.30A
A3984
DMOS Microstepping Driver with Translator
The A3984 is a complete microstepping motor driver with built-in
translator for easy operation. It is designed to operate bipolar stepper
motors in full-, half-, quarter-, and sixteenth-step modes, with an output
drive capacity of up to 35 V and 2 A. The A3984 includes a fixed off-
time current regulator which has the ability to operate in Slow or Mixed
decay modes.
The translator is the key to the easy implementation of the A3984.
Simply inputting one pulse on the STEP input drives the motor one
microstep. There are no phase sequence tables, high frequency control
lines, or complex interfaces to program. The A3984 interface is an ideal
fit for applications where a complex microprocessor is unavailable or is
overburdened.
The chopping control in the A3984 automatically selects the current
decay mode (Slow or Mixed). When a signal occurs at the STEP input
pin, the A3984 determines if that step results in a higher or lower
current in each of the motor phases. If the change is to a higher current,
then the decay mode is set to Slow decay. If the change is to a lower
current, then the current decay is set to Mixed (set initially to a fast
decay for a period amounting to 31.25% of the fixed off-time, then
to a slow decay for the remainder of the off-time). This current decay
control scheme results in reduced audible motor noise, increased step
accuracy, and reduced power dissipation.
Internal synchronous rectification control circuitry is provided to
improve power dissipation during PWM operation.
Internal circuit protection includes: thermal shutdown with hysteresis,
undervoltage lockout (UVLO), and crossover-current protection.
Special power-on sequencing is not required.
The A3984 is supplied in a low-profile (1.2 mm maximum), 24-pin
TSSOP with exposed thermal pad (package LP). It is also available
in a lead (Pb) free version (suffix T), with 100% matte tin plated
leadframes.
Low R
DS(ON)
outputs
Automatic current decay mode detection/selection
Mixed and Slow current decay modes
Synchronous rectification for low power dissipation
Internal UVLO and thermal shutdown circuitry
Crossover-current protection
Use the following complete part number when ordering:
AB SO LUTE MAX I MUM RAT INGS
Part Number
Pb-free
Package
Description
A3984SLP
24-pin, TSSOP
Exposed thermal pad
A3984SLP-T
Yes
Load Supply Voltage,V
BB
...................................35 V
Output Current, I
OUT
......................................... 2 A
*
Logic Input Voltage, V
IN
..................... 0.3 V to 7 V
Sense Voltage, V
SENSE
.......................................0.5 V
Reference Voltage, V
REF
...................................4 V
Operating Temperature Range
Ambient,
T
A
................................. 20C to 85C
Junction Temperature, T
J(MAX)
.....................150C
Storage Temperature, T
S
.................... 55C to 150C
*
Output current rating may be limited by duty cycle,
ambient temperature, and heat sinking. Under any
set of conditions, do not exceed the specified current
rating or a junction temperature of 150C.
Package LP
FEATURES
24
23
22
21
20
19
18
17
16
15
14
13
1
2
3
4
5
6
7
8
9
10
11
12
Transl
at
or
CP1
CP2
VCP
VREG
MS1
MS2
RESET
ROSC
SLEEP
VDD
STEP
REF
GND
ENABLE
OUT2B
VBB2
SENSE2
GND
OUT2A
OUT1A
SENSE1
VBB1
OUT1B
DIR
Ch
a
r
g
e
Pu
m
p
Re
g
OSC
&
C
ontrol
Logi
c
Approximate Scale 1:1
2
26184.30A
Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
A3984
DMOS Microstepping Driver with Translator
Functional Block Diagram
SENSE1
SENSE2
VREG
VCP
CP2
Control
Logic
DAC
VDD
PWM Latch
Blanking
Mixed Decay
DAC
STEP
DIR
RESET
MS1
PWM Latch
Blanking
Mixed Decay
Current
Regulator
CP1
Charge
Pump
R
S2
R
S1
VBB1
OUT1A
OUT1B
VBB2
OUT2A
OUT2B
0.1 uF
V
REF
Translator
Gate
Drive
DMOS Full Bridge
DMOS Full Bridge
0.1 uF
0.22 uF
OSC
ROSC
MS2
REF
ENABLE
SLEEP
3
26184.30A
Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
A3984
DMOS Microstepping Driver with Translator
ELECTRICAL CHARACTERISTICS
1
at T
A
= 25C, V
BB
= 35 V (unless otherwise noted)
1
Negative current is defined as coming out of (sourcing from) the specified device pin.
2
Typical data are for initial design estimations only, and assume optimum manufacturing and application conditions. Performance may vary for
individual units, within the specified maximum and minimum limits.
3
err
I
= (I
Trip
I
Prog
) / I
Prog
, where I
Prog
= %I
TripMAX
I
TripMAX
.
Characteristics
Symbol
Test Conditions
Min.
Typ.
2
Max.
Units
Output Drivers
Load Supply Voltage Range
V
BB
Operating
8
35
V
During Sleep Mode
0
35
V
Logic Supply Voltage Range
V
DD
Operating
3.0
5.5
V
Output On Resistance
R
DSON
Source Driver, I
OUT
= 1.5 A
0.350
0.450
Sink Driver, I
OUT
= 1.5 A
0.300
0.370
Body Diode Forward Voltage
V
F
Source Diode, I
F
= 1.5 A
1.2
V
Sink Diode, I
F
= 1.5 A
1.2
V
Motor Supply Current
I
BB
f
PWM
< 50 kHz
4
mA
Operating, outputs disabled
2
mA
Sleep Mode
10
A
Logic Supply Current
I
DD
f
PWM
< 50 kHz
8
mA
Outputs off
5
mA
Sleep Mode
10
A
Control Logic
Logic Input Voltage
V
IN(1)
V
DD
0.7
V
V
IN(0)
V
DD
0.3
V
Logic Input Current
I
IN(1)
V
IN
= V
DD
0.7
20
<1.0
20
A
I
IN(0)
V
IN
=
V
DD
0.3
20
<1.0
20
A
Microstep Select 2
MS2
50
k
Input Hysteresis
V
HYS(IN)
150
300
500
mV
Blank Time
t
BLANK
0.7
1
1.3
s
Fixed Off-Time
t
OFF
OSC > 3 V
20
30
40
s
R
OSC
= 25 k
23
30
37
s
Reference Input Voltage Range
V
REF
0
4
V
Reference Input Current
I
REF
3
0
3
A
Current Trip-Level Error
3
err
I
V
REF
= 2 V,
%I
TripMAX
=
38.27%
15
%
V
REF
= 2 V,
%I
TripMAX
= 70.71%
5
%
V
REF
= 2 V,
%I
TripMAX
= 100.00%
5
%
Crossover Dead Time
t
DT
100
475
800
ns
Protection
Thermal Shutdown Temperature
T
J
165
C
Thermal Shutdown Hysteresis
T
JHYS
15
C
UVLO Enable Threshold
UV
LO
V
DD
rising
2.35
2.7
3
V
UVLO Hysteresis
UV
HYS
0.05
0.10
V
4
26184.30A
Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
A3984
DMOS Microstepping Driver with Translator
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
20
40
60
80
100
120
140
160
180
Temperature (C)
Power D
i
s
s
i
p
a
t
i
o
n, P
D
(W)
0.0
0.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
1.0
1.5
Maximum Power Dissipation, P
D(max)
(R
JA
= 32 C/W)
Low-K PCB
(R
JA
= 100
C/W)
Minimum-K PCB
(R
JA
= 28
C/W)
High-K PCB
Characteristic
Symbol
Test Conditions*
Value Units
Package Thermal Resistance
R
JA
One-layer PCB, one-sided with copper limited to solder pads
100 C/W
One layer PCB, two-sided with copper limited to solder pads and
3.8 in.
2
of copper area on each side, connected to GND pins
32
C/W
High-K PCB (multilayer with significant copper areas, based on
JEDEC standard)
28
C/W
*In still air. Additional thermal information available on Allegro Web site.
5
26184.30A
Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
A3984
DMOS Microstepping Driver with Translator
Figure 1. Logic Interface Timing Diagram
STEP
t
A
t
D
t
C
MS1, MS2,
RESET, or DIR
t
B
Table 1. Microstep Resolution Truth Table
MS1
MS2 Microstep Resolution
Excitation Mode
L
L
Full Step
2 Phase
H
L
Half Step
1-2 Phase
L
H
Quarter Step
W1-2 Phase
H
H
Sixteenth Step
4W1-2 Phase
Time Duration
Symbol
Typ.
Unit
STEP minimum, HIGH pulse width
t
A
1
s
STEP minimum, LOW pulse width
t
B
1
s
Setup time, input change to STEP
t
C
200
ns
Hold time, input change to STEP
t
D
200
ns
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