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 [phone]
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 [phone]
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 [phone]
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 [phone]
www.allegromicro.com

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