A3981
Automotive, Programmable Stepper Driver
Features and Benefits
• Peak motor current up to ±1.4 A, 28 V
• Low R
DS(on)
outputs, 0.5
Ω
source and sink, typical
• Automatic current decay mode detection/selection
• Mixed, Fast, and Slow current decay modes
• Synchronous rectification for low power dissipation
• Internal OVLO, UVLO, and Thermal Shutdown circuitry
• Crossover-current protection
• Short circuit and open load diagnostics
• Hot and cold thermal warning
• Stall detect features
• SPI-compatible or simple Step and Direction motion control
• Highly configurable via SPI-compatible serial interface
Description
The A3981 is a flexible microstepping motor driver with built-in
translator for easy operation. It is a single-chip solution, designed
to operate bipolar stepper motors in full-, half-, quarter- and
sixteenth-step modes, at up to 28 V and ±1.4 A. The A3981
can be controlled by simple Step and Direction inputs, or
through the SPI-compatible serial interface that also can be
used to program many of the integrated features and to read
diagnostic information.
The current regulator can be programmed to operate in fixed
off-time or fixed frequency PWM, with several decay modes
to reduce audible motor noise and increase step accuracy.
In addition the phase current tables can be programmed via
the serial interface to create unique microstep current
profiles to further improve motor performance for
specific applications.
The current in each phase of the motor is controlled through a
DMOS full bridge, using synchronous rectification to improve
power dissipation. Internal circuits and timers prevent cross-
conduction and shoot-through, when switching between high-
side and low-side drives.
The outputs are protected from short circuits, and features
for low load current and stalled rotor detection are included.
Chip-level protection includes: hot and cold thermal warnings,
overtemperature shutdown, and overvoltage and undervoltage
lockout.
The A3981 is supplied in a 28-pin TSSOP power package with
an exposed thermal pad (package type LP). This package is
lead (Pb) free with 100% matte-tin leadframe plating.
Applications
• Automotive stepper motors
• Engine management
• Headlamp positioning
Package: 28-pin TSSOP with exposed
thermal pad (suffix LP)
Not to scale
Typical Applications
Logic
Supply
CP1 CP2 VCP VBB
VDD
STEP
OAP
DIR
MS0
MS1
OAM
ENABLE
RESETn
DIAG
REF
OBP
Automotive
12V Power Net
Logic
Supply
CP1 CP2 VCP VBB
VDD
STEP
OAP
DIR
MS0
MS1
OAM
ENABLE
RESETn
DIAG
REF
OBP
SDI
SDO
OBM
SCK
STRn
VREG
SENSA
SENSB
OSC
AGND PGND
Automotive
12V Power Net
Micro-
controller
or
ECU
Stepper
Motor
Micro-
controller
or
ECU
Stepper
Motor
SDI
SDO
OBM
SCK
STRn
VREG
SENSA
SENSB
OSC
AGND PGND
Serial Interface Control
A3981-DS, Rev. 5
Parallel Control
A3981
Automotive, Programmable Stepper Driver
Selection Guide
Part Number
A3981KLP-T
A3981KLPTR-T
Packing*
50 pieces per tube
4000 pieces per reel
4.4 mm
×
9.7 mm, 1.2 mm nominal height TSSOP
with exposed thermal pad
*Contact Allegro
™
for additional packing information.
Absolute Maximum Ratings
With respect to GND
Characteristic
Load Supply Voltage
Logic Supply Voltage
Pin CP1
Pins CP2, VCP
Pins STEP, DIR, ENABLE, DIAG
Pin VREG
Pin RESETn
Pin OSC
Pins MS0, MS1
Pins SDI, SDO, SCK, STRn
Pin REF
Pins OAP, OAM, OBP, OBM
Pins SENSA, SENSB
Ambient Operating Temperature
Range
Maximum Continuous Junction
Temperature
Transient Junction Temperature
Storage Temperature Range
T
A
T
J
(max)
T
tJ
T
stg
Overtemperature event not exceeding 10 s,
lifetime duration not exceeding 10 hours,
guaranteed by design and characterization
Range K; limited by power dissipation
Can be pulled to V
BB
with 38 kΩ
Symbol
V
BBx
V
DD
Notes
Applies to V
BBA
and V
BBB
Rating
–0.3 to 50
–0.3 to 6
–0.3 to V
BB
–0.3 to V
BB
+8
–0.3 to 6
–0.3 to 8.5
–0.3 to 6
–0.3 to 6
–0.3 to 6
–0.3 to 6
–0.3 to 6
–0.3 to V
BB
–0.3 to 1
–40 to 150
150
175
–55 to 150
Unit
V
V
V
V
V
V
V
V
V
V
V
V
V
°C
°C
°C
°C
Thermal Characteristics
may require derating at maximum conditions
Characteristic
Package Thermal Resistance
(Junction to Ambient)
Package Thermal Resistance
(Junction to Pad)
Symbol
R
θJA
R
θJP
Test Conditions*
4-layer PCB based on JEDEC standard
2-layer PCB with 24.52
cm
2
of copper area each side
Value
28
32
2
Unit
ºC/W
ºC/W
ºC/W
*Additional thermal information available on the Allegro website
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A3981
Automotive, Programmable Stepper Driver
Functional Block Diagram
3.3V
VDD
OSC
VREG
CP1
CP2
VCP
Oscillator
REF
DAC
REF
Regulator
Charge
Pump
6-bit
DAC
SENSA
DMOS Full Bridge
VBBA
VBAT
+
-
OAP
Translator
STEP
DIR
MS1
MS0
RESETn
ENABLE
PWM
Control
OAM
System
Control
and
Registers
Serial Interface
SENSA
Bridge
Control
Logic
Gate
Drive
DMOS Full Bridge
VBBB
PWM
Control
REF
VBAT
SDI
SDO
SCK
STRn
OBP
OBM
6-bit
DAC
+
-
SENSB
SENSB
DIAG
Undervoltage, Overvoltage
Cold Warning, Hot Warning, Overtemperature
Short Detect, Open Load Detect
Stall Detect
AGND
PAD
PGND
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A3981
Automotive, Programmable Stepper Driver
ELECTRICAL CHARACTERISTICS
1,2
Valid at T
J
= –40°C to 150°C, V
BB
= 7 to 28 V, V
DD
= 3 to 5.5 V; unless otherwise noted
Characteristics
Supplies
Load Supply Voltage Range
3
Load Supply Quiescent Current
Logic Supply Voltage Range
V
BB
I
BBQ
V
DD
ENABLE = 0
Logic Supply Quiescent Current
I
DDQ
ENABLE=0, V
DD
> 5 V
Sleep mode, V
DD
= 3.3 V
Sleep mode, V
DD
= 5 V
Charge Pump Voltage
Internal Regulator Voltage
Internal Regulator Dropout Voltage
Motor Bridge Output
V
BB
= 13.5 V, I
OUT
= –1 A, T
J
= 25°C
High-Side On-Resistance
High-Side Body Diode Forward
Voltage
Low-Side On-Resistance
Low-Side Body Diode Forward
Voltage
R
ONH
V
BB
= 13.5 V, I
OUT
= –1 A, T
J
= 150°C
V
BB
= 7 V, I
OUT
= –1 A, T
J
= 25°C
V
FH
I
F
= 1 A
V
BB
= 13.5 V, I
OUT
= 1 A, T
J
= 25°C
R
ONL
V
BB
= 13.5 V, I
OUT
= 1 A, T
J
= 150°C
V
BB
= 7 V, I
OUT
= 1 A, T
J
= 25°C
V
FL
I
F
= –1 A
ENABLE = 0, RESETn = 1, V
O
= V
BB
Output Leakage Current
I
LO
ENABLE = 0, RESETn = 1, V
O
= 0 V
ENABLE = 0, RESETn = 0, V
O
= V
BB
ENABLE = 0, RESETn = 0, V
O
= 0 V
Current Control
Internal Oscillator Frequency
External Oscillator Frequency Range
Blank Time
4
Off-Time (In Fixed Off-Time Mode)
4
PWM Frequency (In Fixed Frequency
Mode)
4
f
OSC
f
EXT
t
BLANK
t
OFF
f
PWM
Default Blank-Time
Default Off-Time
Default PWM Frequency
OSC = AGND
51 kΩ from OSC to VDD
3.2
3.6
3
–
–
–
4
–
–
1500
44
16.7
4.8
4.4
5
–
–
–
MHz
MHz
MHz
ns
μs
kHz
–
–
–
–
–
–
–
–
–120
–200
–
–20
500
900
625
–
500
900
625
–
–65
–120
<1.0
<1.0
600
1100
750
1.4
600
1100
750
1.4
–
–
20
–
mΩ
mΩ
mΩ
V
mΩ
mΩ
mΩ
V
μA
μA
μA
μA
V
CP
V
REG
V
REGDO
With repect to VBB, V
BB
>7.5 V, ENABLE = 0,
RESETn = 1
ENABLE = 0, RESETn = 1, V
BB
> 7.5 V
ENABLE = 0, RESETn = 1, V
BB
> 5.6 V
Functional
Outputs Driving
ENABLE = 0
Sleep mode
0
7
–
–
3
–
–
–
–
–
–
–
–
–
–
1
–
–
–
4
–
6.7
7.2
100
50
V
BBOV
4
10
5.5
5
5.5
15
25
–
–
200
V
V
mA
μA
V
mA
mA
μA
μA
V
V
mV
Symbol
Test Conditions
Min.
Typ.
Max.
Unit
Continued on the next page…
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A3981
Automotive, Programmable Stepper Driver
otherwise noted
ELECTRICAL CHARACTERISTICS
1,2
(continued) Valid at T
J
= –40°C to 150°C, V
BB
= 7 to 28 V, V
DD
= 3 to 5.5 V; unless
Characteristics
Current Control (continued)
Fast Decay Time
4
Reference Input Voltage
Internal Reference Voltage
Current Control (continued)
Reference Input Current
Maximum Sense Voltage
Current Trip Point Error
5
I
REF
V
SMAX
E
ITrip
V
REF
= 2 V, MxI0 = MxI1 = 1
–3
–
–
–
V
DD
> 4.5 V
–
0.7
×
V
DD
250
0 V < V
IN
< V
DD
I
OL
= 2 mA
I
OL
= –2 mA
0 V < V
O
< V
DD
, STRn = 1
–1
–
–
V
DD
–0.4
–1
0.2
10
–
A in figure 1
B in figure 1
C in figure 1
D in figure 1
E in figure 1
F in figure 1
G in figure 1
H in figure 1
I in figure 1
J in figure 1
K in figure 1
L in figure 1, only when D15 = 1 and D14 = 0
M in figure 1, only when D15 = 1 and D14 = 0
50
50
30
30
300
–
–
–
5
15
10
100
300
0
125
–
–
–
–
500
–
50
0.2
V
DD
–0.2
–
–
–
35
–
–
–
–
–
–
–
–
–
–
–
–
–
3
–
±5
0.3
×
V
DD
0.28
×
V
DD
–
–
1
–
0.4
–
1
4.5
–
–
–
–
–
–
–
40
30
40
–
–
–
–
–
μA
mV
%
V
V
V
mV
μA
kΩ
V
V
μA
μs
μs
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
t
FAST
V
REF
V
REFint
REF tied to VDD
Default Fast Decay Time
–
0.8
1.1
8
–
1.2
–
2
1.3
μs
V
V
Symbol
Test Conditions
Min.
Typ.
Max.
Unit
Logic Input And Output – DC Parameters
Input Low Voltage
Input High Voltage
Input Hysteresis
Input Current (Except RESETn)
Input Pull-Down Resistor (RESETn)
Output Low Voltage
Output High Voltage
Output Leakage (SDO)
Reset Pulse Width
Reset Shutdown Width
Input Pulse Filter Time (STEP, DIR)
Clock High Time
Clock Low Time
Strobe Lead Time
Strobe Lag Time
Strobe High Time
Data Out Enable Time
Data Out Disable Time
Data Out Valid Time from Clock Falling
Data Out Hold Time from Clock Falling
Data In Set-Up Time to Clock Rising
Data In Hold Time From Clock Rising
STEP Rising to STRn Rising
Setup Time
STEP Rising from STRn Rising
Hold Time
V
IL
V
IH
V
Ihys
I
IN
R
PD
V
OL
V
OH
I
O
t
RST
t
RSD
t
PIN
t
SCKH
t
SCKL
t
STLD
t
STLG
t
STRH
t
SDOE
t
SDOD
t
SDOV
t
SDOH
t
SDIS
t
SDIH
t
SPS
t
SPH
Logic Input And Output – Dynamic Parameters
Continued on the next page…
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
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