Data Sheet

29319.35

3974

DMOS DUAL FULL-BRIDGE

PWM MOTOR DRIVER

Designed for pulse-width modulated (PWM) current control

of two dc motors, the A3974SED is capable of output currents to

1.5 A and operating voltages to 50 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.

Independant ENABLE input terminals are provided for use in

controlling the speed and torque of each dc motor with externally
applied PWM control signals.

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

hysteresis, undervoltage monitoring of V

and the charge

pump, and crossover-current protection. Special power-up
sequencing is not required.

The A3974SED is supplied in a 44-lead plastic PLCC with

four copper batwing tabs for maximum heat dissipation. The
power tabs are at ground potential and need no electrical isola-
tion.

FEATURES

1.5 A, 50 V Continuous Output Rating

s Low

DS(on)

DMOS Output Drivers

s Programmable Slow, Fast, and Mixed Current-Decay Modes

s Serial-Interface Controls Chip Functions

s Synchronous Rectification for Low Power Dissipation

s Internal UVLO and Thermal Shutdown Circuitry

s Crossover-Current Protection

s Sleep and Idle Modes

ABSOLUTE MAXIMUM RATINGS

at T

= +25

Load Supply Voltage, V

............................ 50 V

Output Current, I

OUT

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

1.5 A

Logic Supply Voltage, V

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

Logic Input Voltage Range, V

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

+ 0.3 V

< 30 ns ................... -1.0 V to V

+ 1.0 V

Reference Voltage, V

REF

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

Sense Voltage (dc), V

Continous .............................................. 0.5 V
t

< 1

s ................................................ 2.5 V

Package Power Dissipation, P

.................. 3.9 W

Operating Temperature Range,

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

C to +85

Junction Temperature, T

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

Storage Temperature Range,

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

C to +150

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 temperature of 150

Always order by complete part number: A3974SED .

SERIAL PORT

Dwg. PP-073

GND

LOGIC

SUPPLY

GND

SENSE

OUT

STROBE

CLOCK

DATA

GND

REF

OUT

SENSE

GND

LOAD

SUPPLY

ENABLE

OUT

REG

SLEEP

OSC

GND

CP1

CP2

OUT

ENABLE

LOAD

SUPPLY

GND

PROGRAM

PWM TIMER

CHARGE PUMP

BB1

BB2

LOGIC

PROGRAM

PWM TIMER

3974
DMOS DUAL FULL-BRIDGE
PWM MOTOR DRIVER

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

FUNCTIONAL BLOCK DIAGRAM

CHARGE PUMP

BANDGAP

REG

TSD

UNDER-

VOLTAGE &

FAULT DETECT

CHARGE

PUMP

BANDGAP

REGULATOR

BB1

LOGIC

SUPPLY

REG

CP1

CP2

LOAD
SUPPLY

GATE DRIVE

SLEEP

MODE

CONTROL LOGIC

PHASE

SYNC RECT MODE

SYNC RECT DISABLE

MODE

PROGRAMMABLE

PWM TIMER

SENSE

FIXED OFF

BLANK

DECAY

ENABLE

OSC

CLOCK

DATA

STROBE

REFERENCE

BUFFER &

DIVIDER

OUT

REF

PROGRAMMABLE

PWM TIMER

FIXED OFF

BLANK

DECAY

GATE DRIVE

Dwg. FP-048-1

CONTROL LOGIC

PHASE

ENABLE

SYNC RECT MODE

SYNC RECT DISABLE

PWM MODE INT

PWM MODE EXT

SENSE

ENABLE

REFERENCE

BUFFER &

DIVIDER

OUT

REF

REF2

BB2

LOAD
SUPPLY

SERIAL

PORT

CHARGE

PUMP

TO PWM TIMER

ZERO CURRENT DETECT

CURRENT SENSE

ZERO CURRENT DETECT

CURRENT SENSE

3974

DMOS DUAL FULL-BRIDGE

PWM MOTOR DRIVER

www.allegromicro.com

ELECTRICAL CHARACTERISTICS at T

= +25

C, V

= 50 V, V

= 5.0 V, f

PWM

< 50 kHz (unless

otherwise noted).

Limits

Characteristic

Symbol

Test Conditions

Min.

Typ.

Max.

Units

Output Drivers

Load Supply Voltage Range

Operating

During sleep mode

Output Leakage Current

DSS

OUT

= V

<1.0

OUT

= 0 V

<-1.0

-20

Output ON Resistance

DS(on)

Source driver, I

OUT

= -1.5 A

0.5

0.55

Sink driver, I

OUT

= 1.5 A

0.315

0.35

Body Diode Forward Voltage

Source diode, I

= 1.5 A

1.2

Sink diode, I

= 1.5 A

1.2

Load Supply Current

PWM

< 50 kHz

4.0

7.0

Charge pump on, outputs disabled

2.0

5.0

Sleep or idle mode

Control Logic

Logic Supply Voltage Range

Operating

4.5

5.0

5.5

Logic Input Voltage

IN(1)

2.0

IN(0)

0.8

Logic Input Current

IN(1)

= 2.0 V

<1.0

(except ENABLE)

IN(0)

= 0.8 V

<1.0

ENABLE Input Current

EN(1)

= 2.0 V

100

EN(0)

= 0.8 V

OSC Input Frequency

OSC

2.9

6.1

MHz

OSC Input Duty Cycle

OSC Input Hysterisis

200

400

Reference Input Voltage Range

REF

Operating

2.6

continued next page ...

3974
DMOS DUAL FULL-BRIDGE
PWM MOTOR DRIVER

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

Limits

Characteristic

Symbol

Test Conditions

Min.

Typ.

Max.

Units

Control Logic (continued)

Reference Input Current

REF

= 2.6 V

1.0

Reference Input Offset Voltage

Reference Divider Ratio

REF

D16 = 1

D16 = 0

5.0

Gain (G

) Error (note 3)

REF

= 2.6 V, D16 = 0

4.0

REF

= 0.5 V, D16 = 0

REF

= 2.6 V, D16 = 1

4.0

REF

= 0.5 V, D16 = 1

Propagation Delay Time

50% TO 90%:
PWM change to source on

600

750

1000

PWM change to source off

150

350

PWM change to sink on

600

750

1000

PWM change to sink off

150

350

Crossover Delay Time

COD

SR enabled

300

600

1000

Thermal Shutdown Temperature

165

Thermal Shutdown Hysteresis

UVLO Enable Threshold

UVLO

Increasing V

3.9

4.2

4.45

UVLO Hysteresis

UVLO

0.05

0.10

Logic Supply Current

PWM

< 50 kHz

Outputs off

8.0

Idle mode (D18 = 1, D19 = 0)

1.5

Sleep mode (inputs below 0.5 V)

100

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).

ELECTRICAL CHARACTERISTICS at T

= +25

C, V

= 50 V, V

= 5.0 V, f

PWM

< 50 kHz (unless

otherwise noted), continued.

3974

DMOS DUAL FULL-BRIDGE

PWM MOTOR DRIVER

www.allegromicro.com

Serial Interface. The A3974SED 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 20-
bit words: 1 bit to select the word and 19 bits of data. The data
is clocked in starting with D19.

Word 0 Bit Assignments

Select Word 0 (D18 = 0)
Bit

Function

Bridge 1 blank time LSB

Bridge 1 blank time MSB

Bridge 1 off-time LSB

Bridge 1 off-time bit 1

Bridge 1 off-time bit 2

Bridge 1 off-time bit 3

Bridge 1 off-time MSB

Bridge 1 fast-decay time bit LSB

Bridge 1 fast-decay time bit 1

Bridge 1 fast-decay time bit 2

D10

Bridge 1 fast-decay time MSB

D11

Bridge 1 sync. rect. control

D12

Bridge 1 sync. rect. control

D13

Bridge 1 external PWM mode

D14

Bridge 1 enable

D15

Bridge 1 phase

D16

Bridge 1 reference range select

D17

Bridge 1 internal PWM mode

D18

Word select = 0

D19

Test mode

D0 D1 Blank Time. The current-sense comparator is
blanked when any output driver is switched on, according to the
table below. f

osc

is the oscillator input frequency.

Blank Time

4/f

OSC

6/f

OSC

12/f

OSC

24/f

OSC

D2 D6 Fixed Off Time. This five-bit word sets the fixed
off-time for the internal PWM control circuitry. The off-time is
defined by

off

=(8 [1 + N]/f

OSC

) - 1/f

OSC

where N = 0 .... 31

For example, with an oscillator frequency of 4 MHz, the
fixed off-time will be adjustable from 1.75

s to 63.75

s in

increments of 2

D7 D10 Fast Decay Time. This four-bit word sets the fast-
decay portion of the fixed off-time for the internal PWM control
circuitry. This will only have impact if mixed-decay mode is
selected (via bit D17). For t

> t

off

, the device will effectively

operate in fast-decay mode. The fast-decay portion is defined
by

= (8[1 + N]/f

OSC

] - 1/f

OSC

where N = 0 .... 15

For example, with an oscillator frequency of 4 MHz, the fast-
decay time will be adjustable from 1.75

s to 31.75

s in

increments of 2

D11 D12 Synchronous Rectification.

D12

D11

Synchronous Rectifier

Disabled

Low side only

Active

Passive

The different modes of operation are described in the synchro-
nous rectification section of the functional description.

D13 External PWM Decay Mode. This bit determines the
current-decay mode when using ENABLE chopping for
external PWM current control.

D13

Mode

Fast

Slow

FUNCTIONAL DESCRIPTION

continued next page ...

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