ALLEGRO A3985 User Manual
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A3985
Digitally Programmable
Dual Full-Bridge MOSFET Driver
Features and Benefits
▪ 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
Package: 38 pin TSSOP (suffix LD)
Description
The A3985 is a flexible dual full-bridge gate driver suitable
for driving a wide range of higher power industrial bipolar 2phase 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
Approximate size
Continued on the next page…
T ypical Application
3985-DS
A3985
Digitally Programmable
Dual Full-Bridge MOSFET Driver
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
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.
Selection Guide
Part Number Packing*
A3985SLD-T Tube, 50 pieces per tube
A3985SLDTR-T Tape and reel, 4000 pieces per reel
*Contact Allegro for additional packing options
Absolute Maximum Ratings
Characteristic Symbol Notes Rating Units
Supply Voltage V
Logic Supply Voltage V
Logic Inputs and Outputs –0.3 to 7 V
SENSEx pins –1 to 1 V
Sxx pins –2 to 55 V
LSSx pins –2 to 5 V
GHxx pins Sxx to Sxx+15 V
GLxx pins –2 to 16 V V
Cxx pins –0.3 to Sxx+15 V
Operating Ambient Temperature T
Junction Temperature TJ(max) 150 ºC
Storage Temperature T
stg
BB
DD
A
Range S –20 to 85 ºC
–0.3 to 50 V
–0.3 to 7
–55 to 150 ºC
V
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
REF
SDO
SDI
STR
SCK
WC
ENABLE
OSC
VDD
Bandgap Regulator
V
REF
Serial Port
Programmable Divider
Oscillator
VBB
6-bit
DAC
Programmable
PWM Timer
Blanking
Mixed Decay
Phase 1
Control Logic
Phase 2
Control Logic
Programmable
PWM Timer
Blanking
Mixed Decay
6-bit
DAC
V
REF
Phase 1
Phase 2
Protection
UVLO
TSD
Phase 1A
High-Side
Drive
Low-Side
Drive
Phase 1B
Low-Side
Drive
High-Side
Drive
Phase 2A
High-Side
Drive
Low-Side
Drive
Phase 2B
Low-Side
Drive
High-Side
Drive
V
MOTOR
VREG
CREG
C1A
CBOOT1A
GH1A
RGH1A
S1A
V
REG
GL1A
RGL1A
LSS1
SENSE1
GL1B
S1B
GH1B
CBOOT1B
C1B
C2A
CBOOT2A
GH2A
S2A
V
REG
GL2A
LSS2
SENSE2
GL2B
S2B
GH2B
CBOOT2B
C2B
V
RGH2A
RGL2A
Bridge1
RSENSE1
MOTOR
Bridge2
RSENSE2
P
RGH1B
RGL1B
P
RGH2B
RGL2B
P
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
Characteristics Symbol Test Conditions Min. Typ. Max. Units
Supply and Reference
Load Supply Voltage Range V
Load Supply Current I
Load Supply Idle Current I
Logic Supply Voltage Range V
Logic Supply Current I
Logic Supply Idle Current I
Regulator Output V
Bootstrap Diode Forward Voltage V
Gate Output Drive
Turn-On Rise Time t
Turn-Off Fall Time t
Turn-On Propagation Delay t
Turn-Off Propagation Delay t
Crossover Dead Time t
Pull-Up On Resistance R
Pull-Down On Resistance R
Short-Circuit Current – Source
1
Short-Circuit Current – Sink I
DEAD
DS(on)UPIGH
DS(on)DNIGL
I
SC(source)
SC(sink)
GHx Output Voltage V
GLx Output Voltage V
Logic Inputs
Input Low Voltage V
Input High Voltage V
Input Hysteresis V
Input Current
1
Output Low Voltage V
Output High Voltage V
Output Leakage current
1
I
Oleak
= 25°C, VDD = 5 V, VBB = 12 to 50 V, unless noted otherwise
A
BB
f
BB
BBQ
DD
DD
DDQ
REGIREGInt
fBOOTIfBOOT
p(on)
p(off)
MCK
ENABLE = High, outputs disabled – – 6 mA
Word1:Bit D18 = 0 – – 100 μA
Word1:Bit D18 = 0 – – 300 μA
C
r
f
C
LOAD
LOAD
ENABLE low to gate drive on – 120 – ns
ENABLE high to gate drive off – 120 – ns
f
MCK
Word1:Bits D1 and D2 = 00
= 4 MHz, C
= 1000 pF – – 10 mA
LOAD
= 30 mA 11.25 – 13 V
= 10 mA 0.6 0.8 1 V
= 1000 pF, 20% to 80% 80 120 160 ns
= 1000 pF, 80% to 20% 40 60 80 ns
= 4 MHz,
12 – 50 V
3.0 – 5.5 V
– – 10 mA
0.5 – 0.75 μs
= –25 mA 30 40 55 Ω
= 25 mA 14 19 24 Ω
–140 –110 –80 mA
160 200 250 mA
GHx
GLx
IL
IH
IHys
I
IN
OL
OH
CBOOTx fully charged V
SDO, IOL= 0.5 mA
SDO, IOH= –0.3 mA
SDO, STR = 1, 0 V< VO< V
DD
– 0.2 – – V
C
V
REG
0.2
– – 0.3 V
0.7 V
150 300 – mV
–1 – 1 μA
V
DD
0.5
–1
–
DD
–
––V
V
DD
––V
0.5 V
V
1 μA
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
Characteristics Symbol Test Conditions Min. Typ. Max. Units
Current Control
f
Blank Time t
Fixed Off-Time t
BLANK
OFF
MCK
Word1:Bits D1 and D2 = 00
f
MCK
Word1:Bits D3 to D7 = 01010, and
D15 = 0
Reference Input Voltage V
Internal Reference Voltage V
Current Trip Point Error
Reference Input Current
2
1
Internal Oscillator Frequency f
Maximum Clock Input Frequency f
Master Clock Frequency f
REF
REFInt
E
ITrip
I
REF
OSC
EXTmax
MCK
20 kΩ to V
V
REF
R
OSC
External clock selected – 10 – MHz
Protection
VREG Undervoltage Lockout V
VREG Undervoltage Lockout
Hysteresis
V
REGUVHys
VDD Undervoltage Lockout V
VDD Undervoltage Lockout
Hysteresis
V
DDUVHys
Overtemperature Shut Down T
Overtemperature Shut Down
Hysteresis
T
REGUV
DDUV
TSD
TSDHys
Decreasing V
Decreasing V
Temperature increasing – 165 – ºC
Recovery = T
= 25°C, VDD = 5 V, VBB = 12 to 50 V, unless noted otherwise
A
= 4 MHz;
–1–μs
= 4 MHz,
21.75 – 22 μs
0.8 – 2 V
DD
1.9 2.0 2.1 V
= 2 V – – ±5 %
–3 0 3 μA
= 10 kΩ 3.2 4 4.8 MHz
0.5 4 5 MHz
REG
7.5 8 8.5 V
100 200 – mV
DD
2.45 2.7 2.95 V
50 100 – mV
TSD
– T
TSDHys
–15–ºC
Continued on the next page...
THERMAL CHARACTERISTICS
Characteristic Symbol Test Conditions* Value Units
Package Thermal Resistance R
*Additional thermal information available on Allegro Web site.
θJA
4-layer PCB, based on JEDEC standard 47 ºC/W
1-layer PCB with copper limited to solder pads 114 ºC/W
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
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