A2557ELBTR-T - Allegro Microsystems

Description

The A2557 has been specifically designed to provide cost-

effective solutions to relay-driving applications with up to

300 mA drive current per channel. They may also be used for

driving incandescent lamps in applications where turn-on time

is not a concern. Each of the four outputs will sink 300 mA in

the on state. The outputs have a minimum breakdown voltage

of 60 V and a sustaining voltage of 40 V. A low-power Sleep

Mode is activated with either ENABLE low or all inputs low.

In this mode, the supply current drops to below 100 μA.

Overcurrent protection for each channel has been designed into

these devices and is activated at a nominal 500 mA. It protects

each output from short circuits with supply voltages up to 32 V.

When an output experiences a short circuit, the output current

is limited at the 500 mA current clamp. In addition, foldback

circuitry decreases the current limit if an excessive voltage

is present across the output and assists in keeping the device

within its SOA (safe operating area). An exclusive-OR circuit

compares the input and output state of each driver. If either a

short or open load condition is detected, a single FAULT output

is turned on (active low).

29317.16L

Features and Benefits

▪ 300 mA output current per channel

▪ Independent overcurrent protection and thermal limiting

for each driver

▪ Output voltage to 60 V

▪ Output SOA protection

▪ Fault-detection circuitry for open or shorted load

▪ Low quiescent current Sleep Mode

▪ Integral output flyback/clamp diodes

▪ TTL- and 5 V CMOS-compatible inputs

Protected Quad Driver

with Fault Detection and Sleep Mode

Continued on the next page…

Packages:

Functional Block Diagram

Not to scale

A2557

Package EB, 28-pin PLCC

with internally fused pins

Package B, 16-pin DIP

with exposed tabs

Package LB, 16-pin SOIC

with internally fused pins

<<1

OUTN

ENABLE

IN N

FAULT

COMMON CONTROL

ONE OF FOUR DRIVERS

CURRENT

LIMIT

THERMAL

LIMIT

SLEEP

CONTROL

30 A

60 A

2.5 V

VCC

–

Protected Quad Driver

with Fault Detection and Sleep Mode

A2557

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Continuous or multiple overload conditions causing the channel

temperature to reach approximately 165°C will result in an additional

linear decrease in the output current of the affected driver. If the

fault condition is corrected, the output stage will return to its normal

saturated condition.

The packages offer fused leads for enhanced thermal dissipation.

Package B is a 16-pin power DIP with exposed tabs, EB is a 28-

lead power PLCC, and LB is a 16-lead power wide-body SOIC

for surface-mount applications. The lead (Pb) free versions have

100% matte tin leadframe plating.

Description (continued)

Selection Guide

Part Number Pb-free Package Packing Ambient Temperature

(°C)

A2557EB-T* Yes 16-pin DIP, exposed tabs 25 pieces per tube

–40 to 85A2557EEBTR-T* Yes 28-lead PLCC 800 pieces per reel

A2557ELBTR-T* Yes 16-lead SOIC 1000 pieces per reel

A2557KB* – 16-pin DIP, exposed tabs 25 pieces per tube

–40 to 125

A2557KB-T* Yes 16-pin DIP, exposed tabs 25 pieces per tube

A2557KEBTR-T* Yes 28-lead PLCC 800 pieces per reel

A2557KLBTR* – 16-lead SOIC 1000 pieces per reel

A2557KLBTR-T Yes 16-lead SOIC 1000 pieces per reel

A2557SB-T* Yes 16-pin DIP, exposed tabs 25 pieces per tube

–20 to 85A2557SEBTR-T* Yes 28-lead PLCC 800 pieces per reel

A2557SLBTR-T* Yes 16-lead SOIC 1000 pieces per reel

*Variant is in production but has been determined to be NOT FOR NEW DESIGN. This classification indicates that sale of the variant is currently

restricted to existing customer applications. The variant should not be purchased for new design applications because obsolescence in the near future

is probable. Samples are no longer available. Status change: May 4, 2009.

Protected Quad Driver

with Fault Detection and Sleep Mode

A2557

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Absolute Maximum Ratings

Characteristic Symbol Notes Rating Units

Logic Supply Voltage VCC 7.0 V

Input Voltage VI or VOE 7.0 V

Output Voltage VO60 V

Overcurrent Protected Output Voltage VO(OCP) 32 V

Output Current IO

Outputs current-limited to approximately 500 mA

per driver, and TJ limited if higher current is

attempted

500 mA

FAULT Output Voltage VFLT 60 V

Package Power Dissipation PDSee graph – –

Operating Ambient Temperature TA

Range E –40 to 85 ºC

Range K –40 to 125 ºC

Range S –20 to 85 ºC

Maximum Junction Temperature TJ(max) 150 ºC

Storage Temperature Tstg –55 to 150 ºC

50 75 100 125 150

ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS

TEMPERATURE IN oo

ooC

R = 6oC/W

QJT

Dwg. GP-004-2B

SUFFIX 'EB', R = 36oC/W

QJA

SUFFIX 'B', R = 43oC/W

QJA

SUFFIX 'LB', R = 90oC/W

QJA

Protected Quad Driver

with Fault Detection and Sleep Mode

A2557

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

B (DIP) and LB (SOIC) Packages

Note that the A2557xB (DIP) and the A2557xLB

(SOIC) are electrically identical and share a common

terminal number assignment.

314

ENABLE

GROUND

OUT3

FAULT

ROUND

OUT2

OUT1

OUT4

VCC

IN4

IN1

IN2

IN3

Pin-out Diagrams

EB (PLCC) Package

18 26

GROUND

GROUND GROUND

GROUND

Dwg. PP-019-2

CONNECTION

ENABLE

SUPPLY

OUT1

OUT2

OUT3

OUT4

IN4

IN3IN2

IN1

CONNECTION

FAULT

Protected Quad Driver

with Fault Detection and Sleep Mode

A2557

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Limits

Characteristic Symbol Test Conditions Min. Typ. Max. Units

Output Leakage Current* ICEX V

O = 60 V, VI = 0.8 V, VOE = 2.0 V — 30 100 μA

O = 60 V, VI = 2.0 V, VOE = 0.8 V — <1.0 100 μA

Output Sustaining Voltage VO(SUS) IO = 100 mA, VI = VOE = 0.8 V, VCC = Open 40 — — V

Output Saturation Voltage VO(SAT) I

O = 100 mA — 65 200 mV

O = 300 mA — 180 300 mV

Over-Current Limit IOM 5 ms PulseTest, VO = 5.0 V — 500 — mA

Input Voltage VIH INn or ENABLE 2.0 — — V

IL INn or ENABLE — — 0.8 V

Input Current IIH INn or ENABLE, VIH = 2.0 V — — 10 μA

IL INn or ENABLE, VIL = 0.8 V — — -10 μA

Fault Output Leakage Current IFLT V

FLT = 60 V — 4.0 15 μA

FLT = 5 V — <1.0 2.0 μA

Fault Output Current IFLT V

FLT = 5 V, Driver Output Open,

I = 0.8 V, VOE = 2.0 V 40 60 80 μA

Fault Output Saturation Voltage VFLT(SAT) I

FLT = 30 μA — 0.1 0.4 V

Clamp Diode Forward Voltage VF I

F = 500 mA — 1.2 1.7 V

F = 750 mA — 1.5 2.1 V

Clamp Diode Leakage Current IR V

R = 60 V — — 50 μA

Turn-On Delay tPHL I

O = 300 mA, 50% VI to 50% VO — 0.6 10 μs

From Sleep, IO = 300 mA, 50% VI to 50% VO — 3.0 — μs

O = 300 mA, 50% VOE to 50% VO — 1.3 10 μs

Turn-Off Delay tPLH I

O = 300 mA, 50% VI to 50% VO — 2.0 10 μs

O = 300 mA, 50% VOE to 50% VO — 1.4 10 μs

Total Supply Current ICC All Outputs Off — 0.075 0.1 mA

Any One Output On — 12 20 mA

Two Outputs On — 18 30 mA

Three Outputs On — 24 40 mA

All Outputs On — 30 50 mA

Thermal Limit TJ — 165 — °C

ELECTRICAL CHARACTERISTICS over operating temperature range, VCC = 4.75 V to 5.25 V

Typical Data is at TA = +25°C and VCC = 5 V and is for design information only.

Negative current is deﬁ ned as coming out of (sourcing) the speciﬁ ed terminal.

As used here, -100 is deﬁ ned as greater than +10 (absolute magnitude convention) and the minimum is implicitly zero.

* Measurement includes output fault-sensing pull-down current.

Protected Quad Driver

with Fault Detection and Sleep Mode

A2557

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

TYPICAL OPERATING CHARACTERISTICS

100

Dwg. GP-064

200 400

300

OUTPUT CURRENT IN MILLIAMPERES

0.3

0.2

OUTPUT SATURATION VOLTAGE IN VOLTS

0.1

= 5 V

= 125oC

= 25oC

= -40oC

Dwg. GP-065

20 40

OUTPUT VOLTAGE IN VOLTS

600

500

400

300

OUTPUT CURRENT LIMIT IN MILLIAMPERES

= +25oC

= 5 V

100

Dwg. GP-066-1

200 400

300

OUTPUT CURRENT IN MILLIAMPERES

TURN-ON DELAY IN MICROSECONDS

= +25oC

= 5 V

ENABLE SWITCHING

IN SWITCHING (FROM SLEEP)

IN SWITCHING (AWAKE)

100

Dwg. GP-066

200 400

300

OUTPUT CURRENT IN MILLIAMPERES

TURN-OFF DELAY IN MICROSECONDS

= +25oC

= 5 V

ENABLE SWITCHING

IN SWITCHING

Protected Quad Driver

with Fault Detection and Sleep Mode

A2557

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

The A2557 low-current quad power drivers provide protected

output driver functions, combined with a fault diagnostic scheme,

plus an automatic low-current Sleep-Mode function. These de-

vices monitor their outputs for fault (open or shorted) conditions.

For each channel the input and output levels are compared. If

these are different from the expected levels then a fault condition

is ﬂ agged by pulling the common FAULT output low.

Status INNENABLE OUTN FAULT

Normal Load HHLH

LHHH

Sleep Mode XLHH

All L X H H

Over-Current or

Short to Supply HHRL

Open Load or

Short to Ground LHLL

Thermal Fault H H H L

R = Linear drive, current limited.

The FAULT output is operational only if ENABLE is high. The

output state is detected by monitoring the OUTn terminal using a

comparator whose threshold is typically 2.5 V. In order to detect

open-circuit outputs, a 30 μA current sink pulls the output below

the comparator threshold. To ensure correct fault operation, a

minimum load of approximately 1 mA is required. The fault

function is disabled when in ‘sleep’ mode, i.e., FAULT goes high

and the 30 μA output sinks are turned off. The FAULT output is

a switched current sink of typically 60 μA.

Each channel consists of a TTL/CMOS-compatible logic input

gated with a common ENABLE input. A logic high at the input

will provide drive to turn on the output npn switch. Each output

has a current-limit circuit that limits the output current by detect-

ing the voltage drop across a low-value internal resistor in the

emitter of the output switch. If this drop reaches a threshold, then

the base drive to the output switch is reduced to maintain constant

current in the output.

To keep the device within its safe operating area (SOA) this out-

put current limit is further reduced:

• if the power dissipation in the output device increases the

local junction temperature above 165°C (nominal), so as to limit

the power dissipation (and hence the local junction temperature).

As each channel has its own thermal limit circuitry this provides

some independence between the output channels, i.e., one chan-

nel can be operating in thermally reduced current limit, while the

others can provide full drive capability.

• as a function of the output voltage. Full current limit of

500 mA (nominal) is available up to approximately VO = 8 V;

above this the limit is reduced linearly to about 350 mA at VO =

32 V. This helps to improve SOA by immediately reducing the

peak power pulse into a shorted load at high VO.

A logic low at the ENABLE input causes all outputs to be

switched off regardless of the state of the IN terminals. In addi-

tion, the device is put into a low quiescent current ‘sleep’ mode,

reducing ICC below 100 μA. If ENABLE is taken high and any

of the inputs go high, the circuit will ‘auto-wake-up’. However,

if the device is enabled, but all inputs stay low, then the circuit

remains in ‘sleep’ mode.

All outputs have internal ﬂ yback diodes, with a common-cathode

connection at the K terminal.

Incandescent lamp driver

High incandescent lamp turn-on (in-rush currents) can contribute

to poor lamp reliability and destroy semiconductor lamp drivers.

When an incandescent lamp is initially turned on, the cold ﬁ la-

ment is at minimum resistance and would normally allow a 10x

to 12x in-rush current.

Warming (parallel) or current-limiting (series) resistors protect

both driver and lamp but use signiﬁ cant power either when the

lamp is off or when the lamp is on, respectively. Lamps with

steady-state current ratings up to 300 mA can be driven without

the need for warming or current-limiting resistors, if lamp turn-on

time is not a concern (10s of ms).

With these drivers, during turn-on, the high in-rush current is

sensed by the internal sense resistor, drive current to the output

stage is reduced, and the output operates in a linear mode with

the load current limited to approximately 500 mA. During lamp

warmup, the ﬁ lament resistance increases to its maximum value,

the output driver goes into saturation and applies maximum rated

voltage to the lamp.

CIRCUIT DESCRIPTION AND APPLICATION

Protected Quad Driver

with Fault Detection and Sleep Mode

A2557

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

CIRCUIT DESCRIPTION AND APPLICATION (continued)

Fault diagnostics

A pull-up resistor or current source is required on the FAULT

output. This can be connected to whatever supply level the fol-

lowing circuitry requires (within the speciﬁ cation constraints).

For a 5 V supply (i.e., Vcc) 150 kΩ or greater should be used.

As the fault diagnostic function is to indicate when the output

state is different from the input state for any channel, the FAULT

output waveform will obviously produce a pulse waveform fol-

lowing the combined duty-cycle of all channels showing a fault

condition. There are therefore two basic approaches to using the

function in an application:

• As an interrupt in a controller-based system. If the system

has a microcontroller then a FAULT low causes an interrupt,

which then initiates a diagnostic sequence to ﬁ nd the culprit

channel. This sequence usually consists of cycling through each

channel one at a time, while monitoring the FAULT output. It

is then easy to determine which channel has the faulty output

and how it is failing (i.e., short to supply, open-circuit or short to

ground). The system may then take whatever action is required,

but could continue with operation of the remaining ‘good’ chan-

nels while disabling signals to the faulty channel.

• As a simple ‘common’ fault indication. If there is no con-

troller in the system then the FAULT output can be set to give an

indication (via a lamp or LED, etc.) of a fault condition which

might be anywhere on the four channels. Because the FAULT

output is dependent on the states of the input and output (four

possibilities) but will only indicate on two of them, the duty

cycle at the FAULT output will reﬂ ect the duty cycle at the faulty

channel’s input (or its inverse, depending upon fault type).

In typical applications (50% duty cycles) a simple solution is to

make the pull-up current on the FAULT output much less than

the pull-down current (60 μA), and add a capacitor to give a

time constant longer than the period of operation. For typical

values, the device will produce a continuous dc output level.

Component values will need to be adjusted to cope with different

conditions.

Inductive load driver

Biﬁ lar (unipolar) stepper motors (and other inductive loads)

can be driven directly. The internal diodes prevent damage to

the output transistors by suppressing the high-voltage spikes

that occur when turning off an inductive load. For rapid current

decay (fast turn-off speeds), the use of Zener diodes will raise

the ﬂ yback voltage and improve performance. However, the

peak voltage must not exceed the speciﬁ ed minimum sustaining

voltage (VSUPPLY + VZ + VF < VO(SUS)).

Over-current conditions

In the event of a shorted load, or stalled motor, the load current

will attempt to increase. As described above, the drive current to

the affected output stage is linearly reduced, causing the output

to go linear (limiting the load current to about 500 mA). As the

junction temperature of the output stage increases, the thermal-

shutdown circuit will shut off the affected output. If the fault

condition is corrected, the output driver will return to its normal

saturated condition.

NORMAL LAMP IN-RUSH CURRENT

TIME

THERMAL GRADIENT SENSING

CURRENT LIMIT

Dwg. WP-008

NOT TO SCALE

TRIP

LAMP CURRENT

Protected Quad Driver

with Fault Detection and Sleep Mode

A2557

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

CIRCUIT DESCRIPTION AND APPLICATION (continued)

NORMAL LOAD

TIME Dwg. WP-013-1

NOT TO SCALE

OUTPUT CURRENT

CURRENT LIMIT (12 V SUPPLY)

SHORT CIRCUIT

CURRENT LIMIT (24 V SUPPLY)

FAULT

(SHORTED

LOAD)

FAULT

(OPEN

LOAD)

WITH OUTPUT CAPACITOR

Dwg. WP-035

Thermal considerations

Device power dissipation can be calculated as:

PD = (VO1 x IO1 x duty cycle1) + … + (VO4 x IO4 x duty cycle4)

+ (VCC x ICC)

Note - ICC is also modulated by the duty cycle, but this is a rea-

sonable approximation for most purposes.

This can then be compared against the permitted package power

dissipation, using:

Permitted PD = (150 – TA)/RJA

where RJA is given as:

28-lead PLCC (part number sufﬁ x ‘–EB’) = 36°C/W

16-pin PDIP (part number sufﬁ x ‘–B’) = 43°C/W

16-lead SOIC (part number sufﬁ x ‘–LB’) = 90°C/W

RJA is measured on typical two-sided PCB with minimal copper

ground area. Additional information is available on the Allegro

website.

Under some conditions it is possible to get spurious glitches on

the FAULT output at load turn-on and turn-off transitions:

• Light load turn-off. Under light loading conditions the turn-

off delay (see characteristics above) of the output stage increases

and may result in a spurious fault output of a few μs (the dura-

tion being proportional to the turn-off delay). As it is difﬁ cult to

deﬁ ne this over all operating conditions, if a particular applica-

tion would be sensitive to this type of glitch, then it is generally

recommended to include a small (about

0.01 μF) smoothing/storage capacitor at the FAULT output.

• Incandescent lamp turn-on. As described above, driving an

incandescent ﬁ lament results in the driver operating in current

limit for a period after turn-on. During this period a “fault” con-

dition will be indicated (over current). As discussed above this

period can be 10s of ms. To avoid this indication, the capacitor

on the FAULT output would need to be increased to provide an

appropriate time constant. Alternatively, in a microcontroller-

based system, the code could be written to ignore the FAULT

condition for an appropriate period after lamp turn on.

Correct FAULT operation cannot be guaranteed with an uncon-

nected output — unused outputs should not be turned on, or

unused outputs should be pulled high to >2.5 V, and/or associ-

ated inputs tied low.

Protected Quad Driver

with Fault Detection and Sleep Mode

A2557

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

B Package, 16-pin DIP

with internally fused pins 4, 5, 12, and 13

and external thermal tabs

19.05±0.25

5.33 MAX

0.46 ±0.12

1.27 MIN

Dimensions exclusive of mold flash, gate burrs, and dambar protrusions

Exact case and lead configuration at supplier discretion within limits shown

ATerminal #1 mark area

6.35 +0.76

–0.25

3.30 +0.51

–0.38

10.92 +0.38

–0.25

1.52 +0.25

–0.38

0.38 +0.10

–0.05

7.62

2.54

For Reference Only

(reference JEDEC MS-001 BB)

Dimensions in millimeters

Protected Quad Driver

with Fault Detection and Sleep Mode

A2557

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

EB Package, 28-pin PLCC

with internally fused pins 5 through 11 and 19 through 25

2128

Dimensions exclusive of mold flash, gate burrs, and dambar protrusions

Exact case and lead configuration at supplier discretion within limits shown

ATerminal #1 mark area

For Reference Only

(reference JEDEC MS-018 AB)

Dimensions in millimeters

12.45±0.13

4.57 MAX

SEATING

PLANE

C0.10

28X

11.51±0.08

5.21±0.36

5.21±0.36 5.21±0.36

11.51±0.08

0.51

1.27

0.74 ±0.08

0.43 ±0.10

Protected Quad Driver

with Fault Detection and Sleep Mode

A2557

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

LB Package, 16-pin SOIC

with internally fused pins 4 and 5, and 12 and 13

9.50

0.65

2.25

1.27

SEATING

PLANE

C0.10

16X

1.27

0.25

0.20 ±0.10

0.41 ±0.10 2.65 MAX

10.30±0.33

7.50±0.10

4° ±4

0.27 +0.07

–0.06

0.84 +0.44

–0.43

10.30±0.20

GAUGE PLANE

SEATING PLANE

For Reference Only

Pins 4 and 5, and 12 and 13 internally fused

Dimensions in millimeters

(reference JEDEC MS-013 AA)

Dimensions exclusive of mold flash, gate burrs, and dambar protrusions

Exact case and lead configuration at supplier discretion within limits shown

ATerminal #1 mark area

BReference pad layout (reference IPC SOIC127P1030X265-16M)

All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary

to meet application process requirements and PCB layout tolerances

BPCB Layout Reference View

The products described here are manufactured under one or more U.S. patents or U.S. patents pending.

Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to per-

mit improvements in the per for mance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the

information being relied upon is current.

Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the

failure of that life support device or system, or to affect the safety or effectiveness of that device or system.

The in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use;

nor for any in fringe ment of patents or other rights of third parties which may result from its use.

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