3951

3951

Data Sheet

29319.4†

ABSOLUTE MAXIMUM RATINGS

Load Supply Voltage, V

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

Output Current, I

OUT

≤ 20 µs) ..................................

3.5 A

(Continuous) ...............................

2.0 A

Logic Supply Voltage, V

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

Logic Input Voltage Range,

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

+ 0.3 V

Sense Voltage, V

SENSE

........................ 1.5 V

Reference Voltage, V

REF

....................... V

Package Power Dissipation,

....................................... See Graph

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, heat sinking and/or forced

cooling. Under any set of conditions, do not

exceed the specified current rating or a junction

temperature of +150

°C.

* Fault conditions that produce excessive junction

temperature will activate device thermal shutdown

circuitry. These conditions can be tolerated but

should be avoided.

A3951SB

GROUND

LOGIC

SUPPLY

PHASE

GROUND

SENSE

LOAD

SUPPLY

Dwg. PP-056-1

REF/

LOAD

SUPPLY

OUTB

OUTA

LOGIC

ENABLE

BRAKE

Designed for bidirectional pulse-width modulated current control of

inductive loads, the A3951SB and A3951SW are capable of continuous

output currents to

±2 A and operating voltages to 50 V. Internal fixed

off-time PWM current-control circuitry can be used to regulate the

maximum load current to a desired value. The peak load current limit is

set by the user’s selection of an input reference voltage and external

sensing resistor. The fixed off-time pulse duration is set by a user-

selected external RC timing network. Internal circuit protection includes

thermal shutdown with hysteresis, transient suppression diodes, and

crossover-current protection. Special power-up sequencing is not

required. The A3951SB and A3951SW are improved replacements for

the UDN2953B and UDN2954W, respectively. For new system de-

signs, the A3952SB/SEB/SLB/SW are recommended.

With the ENABLE input held low, the PHASE input controls load

current polarity by selecting the appropriate source and sink driver pair.

A user-selectable blanking window prevents false triggering of the PWM

current control circuitry. With the ENABLE input held high, all output

drivers are disabled.

When a logic low is applied to the BRAKE input, the braking

function is enabled. This overrides ENABLE and PHASE to turn off

both source drivers and turn on both sink drivers. The brake function

can be safely used to dynamically brake brush dc motors.

The A3951SB is supplied in a 16-pin dual in-line plastic package

with copper heat-sink contact tabs. The lead configuration enables

easy attachment of a heat sink while fitting a standard printed wiring

board layout. The A3951SW, for higher package power dissipation

requirements, is supplied in a 12-pin single in-line power-tab package.

In either package style, the batwing/power tab is at ground potential

and needs no isolation.

FEATURES

I ±2 A Continuous Output Current Rating

I 50 V Output Voltage Rating

I Internal PWM Current Control

I Internal Transient Suppression Diodes

I Under-Voltage Lockout

I Internal Thermal Shutdown Circuitry

I Crossover-Current Protection

I Default Brake Current Limit

Always order by complete part number:

Part Number

Package

θJA

θJT

A3951SB

16-Pin DIP

°C/W

6.0

°C/W

A3951SW

12-Pin Power-Tab SIP

°C/W

2.0

°C/W

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3951

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Worcester, Massachusetts 01615-0036 (508) 853-5000

LOAD

SUPPLY

PHASE

UVLO

& TSD

R S

Dwg. FP-036-1

REF/

OUT

ENABLE

SENSE

–

BRAKE

INPUT LOGIC

GROUND

1.5 V

PWM LATCH

+ –

BLANKING

VTH

LOGIC

SUPPLY

100

125

150

TEMPERATURE IN

°C

Dwg. GP-032A

SUFFIX 'B', R = 43

°C/W

θJA

SUFFIX 'W', R = 38

°C/W

θJA

SUFFIX 'W',

R = 2.0

°C/W

θJT

SUFFIX 'B',

R = 6.0

°C/W

θJT

ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS

TRUTH TABLE

BRAKE ENABLE PHASE

OUT

DESCRIPTION

Outputs Disabled

Forward

Reverse

Brake, See Note

X = Irrelevant

Z = High Impedance (source and sink both off)

NOTE: Includes internal default V

sense

level for over-current protection.

FUNCTIONAL BLOCK DIAGRAM

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GROUND

Dwg. PP-058-1

LOGIC

SUPPLY

PHASE

SENSE

REF/

LOAD

SUPPLY

OUT

ENABLE

LOGIC

BRAKE

LOAD

SUPPLY

Continued next page …

A3951SW

ELECTRICAL CHARACTERISTICS at T

= +25

C, V

= 50 V, V

= 5.0 V,

REF

= 2.0 V, V

SENSE

= 0 V, RC = 20 k

Ω

/1000 pF to Ground (unless noted otherwise).

Limits

Characteristic

Symbol

Test Conditions

Min.

Typ.

Max.

Units

Output Drivers

Load Supply Voltage Range

Operating, I

OUT

±2.0 A, L = 3 mH

–

Output Leakage Current

CEX

OUT

= V

–

<1.0

µA

OUT

= 0 V

–

<-1.0

-50

µA

Output Saturation Voltage

CE(SAT)

Source driver, I

OUT

= -0.5 A

–

0.9

1.2

Source driver, I

OUT

= -1.0 A

–

1.0

1.4

Source driver, I

OUT

= -2.0 A

–

1.2

1.8

Sink driver, I

OUT

= +0.5 A

–

0.9

1.2

Sink driver, I

OUT

= +1.0 A

–

1.0

1.4

Sink driver, I

OUT

= +2.0 A

–

1.3

1.8

Clamp Diode Forward Voltage

= 0.5 A

–

1.0

1.4

(Source or Sink)

= 1.0 A

–

1.1

1.6

= 2.0 A

–

1.4

2.0

Load Supply Current

BB(ON)

ENABLE

= 0.8 V, V

REF

= 2.0 V

–

2.9

6.0

(No Load)

BB(OFF)

ENABLE

= V

REF

= 2.0 V

–

3.1

6.5

BB(BRAKE)

BRAKE

= 0.8 V

–

3.1

6.5

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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

µA

IN(0)

= 0.8 V

–

<-2.0

-200

µA

Reference Voltage Range

REF

Operating

2.0

–

Reference Input Current

REF

2.0 V

≤ V

REF

≤ V

µA

Reference Voltage Divider Ratio

–

REF

= 5 V

9.5

10.0

10.5

–

PWM RC Fixed Off Time

off

= 1000 pF, R

= 20 k

Ω

µs

PWM Minimum On Time

on(min)

= 820 pF, R

≥ 12 kΩ

–

1.7

3.0

µs

= 1200 pF, R

≥ 12 kΩ

–

2.5

3.8

µs

Propagation Delay Time

OUT

±2.0 A, 50% E

to 90% E

OUT

transition:

ENABLE on to source driver on

–

2.9

–

µs

ENABLE off to source driver off

–

0.7

–

µs

ENABLE on to sink driver on

–

2.4

–

µs

ENABLE off to sink driver off

–

0.7

–

µs

PHASE change to source driver on

–

2.9

–

µs

PHASE change to source driver off

–

0.7

–

µs

PHASE change to sink driver on

–

2.4

–

µs

PHASE change to sink driver off

–

0.7

–

µs

pd(pwm)

Comparator trip to sink driver off

–

0.8

1.5

µs

Thermal Shutdown Temperature

–

165

–

°C

Thermal Shutdown Hysteresis

∆T

–

°C

UVLO Disable Threshold

CC(UVLO)

3.15

3.50

3.85

UVLO Hysteresis

∆V

CC(UVLO)

300

400

500

Logic Supply Current

CC(ON)

ENABLE

= 0.8 V, V

REF

= 2.0 V

–

(No Load)

CC(OFF)

ENABLE

= V

REF

= 2.0 V

–

CC(BRAKE)

REF

= 0.8 V

–

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

2. Each driver is tested separately.

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

Limits

Characteristic

Symbol

Test Conditions

Min.

Typ.

Max.

Units

ELECTRICAL CHARACTERISTICS (Continued)

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FUNCTIONAL DESCRIPTION

INTERNAL PWM CURRENT CONTROL DURING

FORWARD AND REVERSE OPERATION

The A3951SB/SW contain a fixed off-time pulse-width

modulated (PWM) current-control circuit that can be used

to limit the load current to a desired value. The value of

the current limiting (I

TRIP

) is set by the selection of an

external current sensing resistor (R

) and reference input

voltage (V

REF

). The internal circuitry compares the

voltage across the external sense resistor to one tenth the

voltage on the REF input terminal, resulting in a function

approximated by

TRIP

= V

REF

/(10•R

In forward or reverse mode the current-control cir-

cuitry limits the load current. When the load current

reaches I

TRIP

, the comparator resets a latch to turn off the

selected sink driver. The load inductance causes the

current to recirculate through the source driver and

flyback diode (two-quadrant operation or slow decay).

See figure 1.

Figure 1 — Load-Current Paths

The user selects an external resistor (R

) and capaci-

tor (C

) to determine the time period (t

off

= R

•C

) during

which the drivers remain disabled (see “RC Fixed OFF

Time” below). At the end of the R

interval, the drivers

are re-enabled allowing the load current to increase again.

The PWM cycle repeats, maintaining the load current at

the desired value (see figure 2).

Dwg. EP-006-9

R S

DRIVE CURRENT

RECIRCULATION

ENABLE

LOAD

CURRENT

TRIP

Dwg. WP-015-3

Figure 2 — Load-Current Waveform

INTERNAL PWM CURRENT CONTROL DURING

BRAKE MODE OPERATION

The brake circuit turns off both source drivers and

turns on both sink drivers. For dc motor applications, this

has the effect of shorting the motor’s back-EMF voltage,

resulting in current flow that brakes the motor dynamically.

However, if the back-EMF voltage is large and there is no

PWM current limiting, then the load current can increase to

a value that approaches a locked rotor condition. To limit

the current, when the I

TRIP

level is reached, the PWM

circuit disables the conducting sink driver. The energy

stored in the motor’s inductance is then discharged into

the load supply causing the motor current to decay.

As in the case of forward/reverse operation, the drivers

are re-enabled after a time given by t

off

= R

•C

(see “RC

Fixed Off Time” below). Depending on the back-EMF

voltage (proportional to the motor’s decreasing speed), the

load current again may increase to I

TRIP

. If so, the PWM

cycle will repeat, limiting the load current to the desired

value.

Brake Operation

During braking, the peak current limit defaults inter-

nally to a value approximated by

TRIP

= 1.5 V/R

In this mode, the value of R

determines the I

TRIP

value

independent of V

REF

. This is useful in applications with

differing run and brake currents and no practical method of

varying V

REF

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Choosing a small value for R

essentially disables the

current limiting during braking. Therefore, care should be

taken to ensure that the motor’s current does not exceed

the absolute maximum ratings of the device. The braking

current can be measured by using an oscilloscope with a

current probe connected to one of the motor’s leads.

CAUTION: Because the kinetic energy stored in the

motor and load inertia is being converted into current,

which charges the V

supply bulk capacitance (power

supply output and decoupling capacitance), care must be

taken to ensure the capacitance is sufficient to absorb the

energy without exceeding the voltage rating of any devices

connected to the motor supply.

RC Fixed Off Time

The internal PWM current control circuitry uses a one

shot to control the time the driver remains off. The one

shot time, t

off

(fixed off time), is determined by the selection

of an external resistor (R

) and capacitor (C

) connected in

parallel from the RC terminal to ground. The fixed off time,

over a range of values of C

= 820 pF to 1500 pF and R

12 k

Ω to 100 kΩ, is approximated by

off

= R

•C

When the PWM latch is reset by the current compara-

tor, the voltage on the RC terminal will begin to decay from

approximately 3 volts. When the voltage on the RC

terminal reaches approximately 1.1 volts, the PWM latch is

set, thereby re-enabling the driver.

RC Blanking

In addition to determining the fixed off time of the

PWM control circuit, the C

component sets the compara-

tor blanking time. This function blanks the output of the

comparator when the outputs are switched by the internal

current control circuitry (or by the PHASE, BRAKE, or

ENABLE inputs). The comparator output is blanked to

prevent false over-current detections due to reverse

recovery currents of the clamp diodes, and/or switching

transients related to distributed capacitance in the load.

During internal PWM operation, at the end of the off

time, the comparator’s output is blanked and C

begins to

be charged from approximately 1.1 V by an internal current

source of approximately 1 mA. The comparator output

remains blanked until the voltage on C

reaches approxi-

mately 3.0 volts.

Similarly, when a transition of the PHASE input occurs,

is discharged to near ground during the crossover delay

time (the crossover delay time is present to prevent

simultaneous conduction of the source and sink drivers).

After the crossover delay, C

is charged by an internal

current source of approximately 1 mA. The comparator

output remains blanked until the voltage on C

reaches

approximately 3.0 volts.

Similarly, when the device is disabled via the ENABLE

input, C

is discharged to near ground. When the device is

re-enabled, C

is charged by the internal current source.

The comparator output remains blanked until the voltage

on C

reaches approximately 3.0 V.

For most applications, the minimum recommended

value is C

= 820 pF

±5 %. This value ensures that the

blanking time is sufficient to avoid false trips of the com-

parator under normal operating conditions. For optimal

regulation of the load current, the above value for C

recommended and the value of R

can be sized to deter-

mine t

off

. For more information regarding load current

regulation, see below.

LOAD CURRENT REGULATION WITH THE INTERNAL

PWM CURRENT-CONTROL CIRCUITRY

During operation, the A3951S– have a lower limit to

the range of PWM current control. This directly relates to

the limitations imposed by the V

REF

input (2.0 V, minimum).

Applications requiring a broader or full range (

≈0% to

100%) should utilize the A3952S–, which are recom-

mended for the improvements they bring to new designs.

LOAD CURRENT REGULATION WITH EXTERNAL

PWM OF THE PHASE OR ENABLE INPUTS

The PHASE or ENABLE inputs can be pulse-width

modulated to regulate load current. Typical propagation

delays from the PHASE and ENABLE inputs to transitions

of the power outputs are specified in the electrical charac-

teristics table. If the normal PWM current control is used,

then the comparator blanking function is active during

phase and enable transitions. This eliminates false

tripping of the over-current comparator caused by switch-

ing transients (see “RC Blanking” above).

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ENABLE

LOAD

CURRENT

TRIP

Dwg. WP-015-4

Dwg. EP-006-10

R S

DRIVE CURRENT

RECIRCULATION

Figure 3 — Load-Current Paths

NABLE

Pulse-Width Modulation

Toggling the ENABLE input turns on and off the

selected source and sink drivers; the load inductance

causes the current to flow from ground to the load supply

via the ground clamp and flyback diodes (four-quadrant

operation or fast decay). See figure 3. When the device is

enabled, the internal current-control circuitry will be active

and can be used to limit the load current in the normal

internal PWM slow-decay or two-quadrant mode of opera-

tion.

Figure 4 — ENABLE PWM Load-Current Waveform

HASE

Pulse-Width Modulation

Toggling the PHASE terminal determines/controls

which sink/source pair is enabled, producing a load current

that varies with the duty cycle and remains continuous at

all times. This can have added benefits in bidirectional

brush dc servo motor applications as the transfer function

between the duty cycle on the phase input and the aver-

age voltage applied to the motor is more linear than in the

case of ENABLE PWM control (which produces a discon-

tinuous current at low current levels). See also, “DC Motor

Applications” below.

MISCELLANEOUS INFORMATION

An internally generated dead time prevents crossover

currents that can occur when switching phase or braking.

Thermal protection circuitry turns off all drivers should

the junction temperature reach 165

°C (typical). This is

intended only to protect the device from failures due to

excessive junction temperatures and should not imply that

output short circuits are permitted. The hysteresis of the

thermal shutdown circuit is approximately 15

°C.

If the internal current-control circuitry is not used; the

REF

terminal should be connected to V

, the SENSE

terminal should be connected to ground, and the RC

terminal should be left floating (no connection).

An internal under-voltage lockout circuit prevents

simultaneous conduction of the outputs when the device is

powered up or powered down.

APPLICATIONS NOTES

Current Sensing

The actual peak load current (I

OUTP

) will be greater

than the calculated value of I

TRIP

due to delays in the turn

off of the drivers. The amount of overshoot can be ap-

proximated as

OUTP

≈

– ((I

TRIP

• R

LOAD

) + V

BEMF

)) •

pd(pwm)

LOAD

where V

is the load/motor supply voltage, V

BEMF

is the

back-EMF voltage of the load, R

LOAD

and L

LOAD

are the

resistance and inductance of the load respectively, and

pd(pwm)

is the propagation delay as specified in the electrical

characteristics table.

The reference terminal has an equivalent input resis-

tance of 50 k

Ω ±30%. This should be taken into account

when determining the impedance of the external circuit

that sets the reference voltage value.

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To minimize current-sensing inaccuracies caused by

ground trace I•R drops, the current-sensing resistor should

have a separate return to the ground terminal of the

device. For low-value sense resistors, the I•R drops in the

PCB can be significant and should be taken into account.

The use of sockets should be avoided as contact resis-

tance can cause variations in the effective value of R

Larger values of R

reduce the aforementioned effects

but can result in excessive heating and power loss in the

sense resistor. The selected value of R

must not result in

the SENSE terminal absolute maximum voltage rating

being exceeded. The recommended value of R

is in the

range of

= (0.375 to 1.125)/I

TRIP

Thermal Considerations

For the most reliable operation, it is recommended that

the maximum junction temperature be kept as low as

practical, preferably below 125

°C. The junction tempera-

ture can be measured by attaching a thermocouple to the

power tab/batwing of the device and measuring the tab

temperature, T

. The junction temperature then can be