A3985
Digitally Programmable
Dual Full-Bridge MOSFET Driver
Features and Benefits
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Serial interface for full digital control
Dual full-bridge gate drive for N-channel MOSFETs
Dual 6-bit DAC current reference
Operation over 12 to 50 V supply voltage range
Synchronous rectification
Cross-conduction protection
Adjustable mixed decay
Fixed off-time PWM current control
Low-current idle mode
Description
The A3985 is a flexible dual full-bridge gate driver suitable
for driving a wide range of higher power industrial bipolar 2-
phase stepper motors or 2-phase brushless dc motors. It can
also be used to drive two individual torque motors or solenoid
actuators. Motor power is provided by external N-channel power
MOSFETs at supply voltages from 12 to 50 V.
Full digital control is provided by two serially-accessible
registers that allow programming of off-time, blank-time,
dead-time, mixed decay ratios, synchronous rectification,
master clock source selection, and division ratio and idle
mode. All internal timings are derived from a master clock
that can be generated on-chip or provided by an external
clock such as the system clock of the master controller. A
programmable divider allows for a wide range of external
system clock frequencies.
The internal fixed off-time PWM current-control timing is
programmed via the serial interface to operate in slow, fast,
and mixed current-decay modes. The desired load-current level
and direction is set via the serial port with a direction bit and
two 6-bit linear DACs in conjunction with a reference voltage.
The seven bits of control allow maximum flexibility in torque
Continued on the next page…
Package: 38 pin TSSOP (suffix LD)
Approximate size
Typical Application
3985-DS
A3985
Digitally Programmable
Dual Full-Bridge MOSFET Driver
are protected from shoot-through by integrated crossover-control
and programmable dead time.
In addition to crossover current control, internal circuit protection
provides thermal shutdown with hysteresis and undervoltage lockout.
Special power-up sequencing is not required. This component is
supplied in a 38-pin TSSOP (package LD) with 100% matte tin
leadframe plating.
Description (continued)
control for a variety of step methods, from microstepping to full-step
drive. Load current in the external power MOSFET full-bridges is
set in 1.56% increments of the maximum value.
The above-supply voltage required for the high-side N-channel
MOSFETs is provided by a bootstrap capacitor. Efficiency is
enhanced by using synchronous rectification and the power FETs
Selection Guide
Part Number
A3985SLD-T
A3985SLDTR-T
Packing*
Tube, 50 pieces per tube
Tape and reel, 4000 pieces per reel
*Contact Allegro for additional packing options
Absolute Maximum Ratings
Characteristic
Supply Voltage
Logic Supply Voltage
Logic Inputs and Outputs
SENSEx pins
Sxx pins
LSSx pins
GHxx pins
GLxx pins
Cxx pins
Operating Ambient Temperature
Junction Temperature
Storage Temperature
T
A
T
J
(max)
T
stg
Range S
Symbol
V
BB
V
DD
Notes
Rating
–0.3 to 50
–0.3 to 7
–0.3 to 7
–1 to 1
–2 to 55
–2 to 5
Sxx to Sxx+15
–2 to 16 V
–0.3 to Sxx+15
–20 to 85
150
–55 to 150
Units
V
V
V
V
V
V
V
V
V
ºC
ºC
ºC
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
2
A3985
Digitally Programmable
Dual Full-Bridge MOSFET Driver
Functional Block Diagram
+5 V
VDD
VBB
V
MOTOR
VREG
Bandgap
Regulator
CREG
Phase 1A
Bridge1
CBOOT1A
REF
V
REF
High-Side
Drive
V
REG
6-bit
DAC
Low-Side
Drive
GL1A
LSS1
SENSE1
Phase 1B
Low-Side
Drive
Phase 1
SDI
Phase 1
Control Logic
High-Side
Drive
GH1B
CBOOT1B
C1B
STR
Serial Port
GL1B
S1B
RSENSE1
P
P
C1A
GH1A
S1A
RGH1A
RGH1B
RGL1A
RGL1B
SDO
Programmable
PWM Timer
Blanking
Mixed Decay
V
MOTOR
Bridge2
Phase 2A
C2A
CBOOT2A
SCK
Phase 2
Control Logic
Phase 2
High-Side
Drive
V
REG
Low-Side
Drive
GH2A
S2A
RGH2A
RGH2B
GL2A
LSS2
SENSE2
RGL2A
RGL2B
WC
Programmable
PWM Timer
Blanking
Mixed Decay
Phase 2B
Low-Side
Drive
GL2B
S2B
GH2B
CBOOT2B
C2B
RSENSE2
P
6-bit
DAC
ENABLE
V
REF
Programmable Divider
Oscillator
Protection
UVLO
TSD
High-Side
Drive
OSC
GND
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
3
A3985
Digitally Programmable
Dual Full-Bridge MOSFET Driver
ELECTRICAL CHARACTERISTICS
at T
A
= 25°C, V
DD
= 5 V, V
BB
= 12 to 50 V, unless noted otherwise
Characteristics
Supply and Reference
Load Supply Voltage Range
Load Supply Current
Load Supply Idle Current
Logic Supply Voltage Range
Logic Supply Current
Logic Supply Idle Current
Regulator Output
Bootstrap Diode Forward Voltage
Gate Output Drive
Turn-On Rise Time
Turn-Off Fall Time
Turn-On Propagation Delay
Turn-Off Propagation Delay
Crossover Dead Time
Pull-Up On Resistance
Pull-Down On Resistance
Short-Circuit Current – Source
1
Short-Circuit Current – Sink
GHx Output Voltage
GLx Output Voltage
Logic Inputs
Input Low Voltage
Input High Voltage
Input Hysteresis
Input Current
1
Output Low Voltage
Output High Voltage
Output Leakage current
1
Symbol
V
BB
I
BB
I
BBQ
V
DD
I
DD
I
DDQ
V
REG
V
fBOOT
t
r
t
f
t
p(on)
t
p(off)
t
DEAD
f
MCK
= 4 MHz, C
LOAD
= 1000 pF
ENABLE = High, outputs disabled
Word1:Bit D18 = 0
Test Conditions
Min.
12
–
–
–
3.0
–
–
11.25
0.6
80
40
–
–
0.5
30
14
–140
160
V
C
– 0.2
V
REG
–
0.2
–
0.7 V
DD
150
–1
SDO, I
OL
= 0.5 mA
SDO, I
OH
= –0.3 mA
SDO, STR = 1, 0 V< V
O
< V
DD
V
DD
–
0.5
–1
1
Typ.
–
–
–
–
–
–
–
–
0.8
120
60
120
120
–
40
19
–110
200
–
–
–
–
300
–
Max.
50
10
6
100
5.5
10
300
13
1
160
80
–
–
0.75
55
24
–80
250
–
–
0.3 V
DD
–
–
1
0.5
Units
V
mA
mA
μA
V
mA
μA
V
V
ns
ns
ns
ns
μs
Ω
Ω
mA
mA
V
V
V
V
mV
μA
V
V
μA
Word1:Bit D18 = 0
I
REGInt
= 30 mA
I
fBOOT
= 10 mA
C
LOAD
= 1000 pF, 20% to 80%
C
LOAD
= 1000 pF, 80% to 20%
ENABLE low to gate drive on
ENABLE high to gate drive off
f
MCK
= 4 MHz,
Word1:Bits D1 and D2 = 00
I
GH
= –25 mA
I
GL
= 25 mA
R
DS(on)UP
R
DS(on)DN
I
SC(source)
I
SC(sink)
V
GHx
CBOOTx fully charged
V
GLx
V
IL
V
IH
V
IHys
I
IN
V
OL
V
OH
I
Oleak
Continued on the next page...
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
4
A3985
Digitally Programmable
Dual Full-Bridge MOSFET Driver
ELECTRICAL CHARACTERISTICS,
continued, at T
A
= 25°C, V
DD
= 5 V, V
BB
= 12 to 50 V, unless noted otherwise
Characteristics
Symbol
Test Conditions
Min.
Typ.
Max.
Current Control
f
MCK
= 4 MHz;
Blank Time
t
BLANK
–
1
–
Word1:Bits D1 and D2 = 00
f
MCK
= 4 MHz,
Fixed Off-Time
t
OFF
Word1:Bits D3 to D7 = 01010, and
21.75
–
22
D15 = 0
Reference Input Voltage
V
REF
0.8
–
2
Internal Reference Voltage
V
REFInt
20 kΩ to V
DD
1.9
2.0
2.1
Current Trip Point Error
2
E
ITrip
V
REF
= 2 V
–
–
±5
Reference Input Current
1
I
REF
–3
0
3
Internal Oscillator Frequency
f
OSC
R
OSC
= 10 kΩ
3.2
4
4.8
Maximum Clock Input Frequency
f
EXTmax
External clock selected
–
10
–
Master Clock Frequency
f
MCK
0.5
4
5
Protection
VREG Undervoltage Lockout
V
REGUV
Decreasing V
REG
7.5
8
8.5
VREG Undervoltage Lockout
V
REGUVHys
100
200
–
Hysteresis
VDD Undervoltage Lockout
V
DDUV
Decreasing V
DD
2.45
2.7
2.95
VDD Undervoltage Lockout
V
DDUVHys
50
100
–
Hysteresis
Overtemperature Shut Down
T
TSD
Temperature increasing
–
165
–
Overtemperature Shut Down
–
15
–
T
TSDHys
Recovery = T
TSD
– T
TSDHys
Hysteresis
Units
μs
μs
V
V
%
μA
MHz
MHz
MHz
V
mV
V
mV
ºC
ºC
Continued on the next page...
THERMAL CHARACTERISTICS
Characteristic
Package Thermal Resistance
Symbol
R
θJA
Test Conditions*
4-layer PCB, based on JEDEC standard
1-layer PCB with copper limited to solder pads
Value Units
47
114
ºC/W
ºC/W
*Additional thermal information available on Allegro Web site.
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
5
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