SERIAL PORT

6-BIT DAC

& LOGIC

GROUND

SLEEP

REG

OUT

LOAD
SUPPLY

SENSE

OUT

LOGIC
SUPPLY

MUX

REF

Dwg. PP-069-3

GROUND

VCP

CP1

CP2

OUT

STROBE

CLOCK

DATA

SENSE

LOAD

SUPPLY

CHARGE

PUMP

OSC

BB2

BB1

6-BIT DAC

& LOGIC

Data Sheet

29319.34

3973

DUAL DMOS FULL-BRIDGE MICRO-

STEPPING PWM MOTOR DRIVER

Designed for pulse-width modulated (PWM) current control of

bipolar microstepping stepper motors, the A3973SB and A3973SLB are
capable of continuous output currents to

±1 A and operating voltages to

35 V. Internal fixed off-time PWM current-control timing circuitry can
be programmed via a serial interface to operate in slow, fast, and mixed
current-decay modes. The A3973SB (DIP) and the A3973SLB (SOIC)
are electrically identical and differ only in package style.

The desired load-current level is set via the serial port with two 6-bit

linear DACs in conjunction with a reference voltage. The six bits of
control allow maximum flexibility in torque control for a variety of step
methods, from microstepping to full-step drive. Load current is set in
1.56% increments of the maximum value.

Synchronous rectification circuitry allows the load current to flow

through the low

DS(on)

of the DMOS output driver during the current

decay. This feature will eliminate the need for external clamp diodes in
most applications, saving cost and external component count, while
minimizing power dissipation.

Internal circuit protection includes thermal shutdown with hyster-

esis, transient-suppression diodes, and crossover-current protection.
Special power-up sequencing is not required.

The A3973SB is supplied in a 24-lead plastic DIP with a copper

batwing power tab; the A3973SLB is supplied in a 24-lead plastic SOIC
with a copper batwing power tab for surface-mount applications. The
power tabs are at ground potential and need no electrical isolation.

FEATURES

I ±1 A, 35 V Continuous Output Rating
I Low

DS(on)

DMOS Output Drivers

I Optimized Microstepping via 6-Bit Linear DACs
I Programmable Mixed, Fast, and Slow Current-Decay Modes
I 4 MHz Internal Oscillator for Digital Timing
I Serial-Interface Controls Chip Functions
I Synchronous Rectification for Low Power Dissipation
I Internal UVLO and Thermal Shutdown Circuitry
I Crossover-Current Protection
I Precision 2 V Reference
I Inputs Compatible with 3.3 V or 5 V Control Signals
I Sleep and Idle Modes

PRELIMINARY INFORMATION

(Subject to change without notice)

December 1, 2000

ABSOLUTE MAXIMUM RATINGS

at T

= +25

°C

Load Supply Voltage, V

................ 35 V

Output Current, I

OUT

......................

±1.0 A

Logic Supply Voltage, V

.............. 7.0 V

Logic Input Voltage Range,

................ -0.3 V to V

+ 0.3 V

Reference Voltage, V

REF

..................... 3 V

Sense Voltage (dc), V

................ 500 mV

Package Power Dissipation, P

A3973SB ............................... 3.1 W
A3973SLB ............................ 2.2 W

Operating Temperature Range,

.......................... -20

°C to +85°C

Junction Temperature, T

............. +150

°C

Storage Temperature Range,

......................... -55

°C to +150°C

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 tempera-
ture of 150

°C.

Always order by complete part number, e.g., A3973SB .

3973
DUAL DMOS FULL-BRIDGE
MICROSTEPPING PWM MOTOR DRIVER

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

FUNCTIONAL BLOCK DIAGRAM

CONTROL

LOGIC

REGULATOR

UVLO AND

FAULT

DETECT

OUT

SENSE

GATE

DRIVE

CHARGE PUMP

REG

CP1

CP2

BB1

BANDGAP

OSC

SERIAL

PORT

CLOCK

DATA

STROBE

OUT

0.22

µF

PHASE 1/2
SYNC. RECT. MODE

SYNC. RECT. DISABLE
MODE 1/2

0.22

µF

0.22

µF

REF

OUT

BB2

OUT

SENSE

PROGRAMMABLE

PWM TIMER

FIXED-OFF
BLANK
MIXED DECAY

PROGRAMMABLE

PWM TIMER

FIXED-OFF
BLANK
MIXED DECAY

6-BIT
LINEAR
DAC

SENSE

2 V

GROUND

MUX

OSCILATOR

OSC SELECT/

DIVIDER

BUFFER

0.1

µF

SLEEP

DMOS H-BRIDGE

18 19

LOAD

SUPPLY

LOGIC

SUPPLY

0.1

µF

Dwg. FP-050-1

6-BIT
LINEAR
DAC

3973

DUAL DMOS FULL-BRIDGE

MICROSTEPPING PWM MOTOR DRIVER

www.allegromicro.com

ELECTRICAL CHARACTERISTICS at T

= +25

C, V

= 35 V, V

= 5.0 V, V

= 0.5 V,

PWM

< 50 kHz (unless otherwise noted).

Limits

Characteristic

Symbol

Test Conditions

Min.

Typ.

Max.

Units

Load Supply Voltage Range

Operating

During sleep mode

Logic Supply Voltage Range

Operating

4.5

5.0

5.5

Load Supply Current

PWM

< 50 kHz

8.0

Operating, outputs disabled

6.0

Sleep or idle mode

µA

Logic Supply Current

PWM

< 50 kHz

Outputs off

Idle mode (D0 = 1, D18 = 0)

1.5

Sleep mode

100

µA

Output Drivers

Output Leakage Current

DSS

OUT

= V

<1.0

µA

OUT

= 0 V

<-1.0

-50

µA

Output On Resistance

DS(on)

Source driver, I

OUT

= 1.0 A

0.54

0.60

Sink driver, I

OUT

= 1.0 A

0.54

0.60

Body Diode Forward Voltage

Source diode, I

= 1.0 A

1.2

Sink diode, I

= 1.0 A

1.2

Control Logic

Logic Input Voltage

IN(1)

2.0

IN(0)

0.8

Logic Input Current

IN(1)

= 2.0 V

<1.0

µA

IN(0)

= 0.8 V

<-2.0

-20

µA

OSC Input Frequency Range

OSC

Divide by one

2.5

6.0

MHz

(D0 =1, D13 = 0, D14 = 1)

OSC Input Duty Cycle

Input Hysterisis

0.20

0.40

continued next page ...

3973
DUAL DMOS FULL-BRIDGE
MICROSTEPPING PWM MOTOR DRIVER

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

ELECTRICAL CHARACTERISTICS at T

= +25

C, V

= 35 V, V

= 5.0 V, V

= 0.5 V,

PWM

< 50 kHz (unless otherwise noted).

Limits

Characteristics

Symbol

Test Conditions

Min.

Typ.

Max.

Units

Control Logic (continued)

Internal Oscillator

OSC

OSC shorted to ground

3.0

4.0

5.0

MHz

OSC

= 51 k

3.4

4.0

4.6

MHz

DAC Accuracy (total error)

Relative to DAC reference buffer

±1/2

LSB

output, D0 = 0, D17 = 0

Reference Input Voltage Range

REF(EXT)

0.5

2.6

Reference Buffer Offset

±10

Reference Divider Ratio

REF

D0 = 0, D18 = 0

8.0

D0 = 0, D18 = 1

4.0

Reference Input Current

REF

= 2.0 V

±0.5

µA

Internal Reference Voltage

REF(INT)

1.94

2.0

2.06

Gain (G

) Error (note 3)

D0 = 0, D17 = 0,

D18 = 0, DAC = 63

±6

D18 = 0, DAC = 31

±9

D18 = 1, DAC = 63

±6

D18 = 1, DAC = 15

±10

Comparator Input Offset Voltage

REF

= 0 V

±5.0

Propagation Delay Times

50% to 90%:

PWM change to source on

500

800

1200

PWM change to source off

150

350

PWM change to sink on

500

800

1200

PWM change to sink off

150

350

Crossover Dead Time

300

700

900

Thermal Shutdown Temperature

165

°C

Thermal Shutdown Hysteresis

°C

UVLO Enable Threshold

UVLO

Increasing V

3.9

4.2

4.45

UVLO Hysteresis

UVLO

0.05

0.10

NOTES: 1. Typical Data is for design information only.

2. Negative current is defined as coming out of (sourcing) the specified device terminal.
3. E

= [(V

REF

/Range) V

]/(V

REF

/Range).

3973

DUAL DMOS FULL-BRIDGE

MICROSTEPPING PWM MOTOR DRIVER

www.allegromicro.com

Serial Interface. The A3973SB/SLB is controlled via a
3-wire (clock, data, strobe) serial port. The programmable
functions allow maximum flexibility in configuring the PWM to
the motor drive requirements. The serial data is written as two
19-bit words: 1 bit to select the word and 18 bits of data. The
serial data is clocked in starting with D18.

Word 0 Bit Assignments

Bit

Function

Word select = 0

Bridge 1, DAC, LSB

Bridge 1, DAC, bit 2

Bridge 1, DAC, bit 3

Bridge 1, DAC, bit 4

Bridge 1, DAC, bit 5

Bridge 1, DAC, MSB

Bridge 2, DAC, LSB

Bridge 2, DAC, bit 2

Bridge 2, DAC, bit 3

D10

Bridge 2, DAC, bit 4

D11

Bridge 2, DAC, bit 5

D12

Bridge 2, DAC, MSB

D13

Bridge 1 phase

D14

Bridge 2 phase

D15

Bridge 1 mode

D16

Bridge 2 mode

D17

REF select

D18

Range select

D1 D6 Bridge 1 Linear DAC. Six-bit word sets desired
current level for Bridge 1. Setting all six bits to zero disables
Bridge 1, with all drivers off (See current regulation section of
functional description).

D7 D12 Bridge 2 Linear DAC. Six-bit word sets desired
current level for Bridge 2. Setting all six bits to zero disables
Bridge 2, with all drivers off (See current regulation section of
functional description).

FUNCTIONAL DESCRIPTION

continued next page ...

D13 Bridge 1 Phase. This bit controls the direction of
output current for Load 1.

D13

OUT

D14 Bridge 2 Phase. This bit controls the direction of
output current for Load 2.

D14

OUT

D15 Bridge 1 Mode.

D15

Mode

Mixed-decay

Slow-decay

D16 Bridge 2 Mode.

D16

Mode

Mixed-decay

Slow-decay

D17 REF Select. This bit determines the reference input for
the 6-bit linear DACs.

D17

Reference Voltage

Internal 2 V

External (3 V max)

D18 G

Range Select. This bit determines the scaling factor

(4 or 8) used.

D18

Divider

Load Current

1/8

TRIP

= V

DAC

/8R

1/4

TRIP

= V

DAC

/4R

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