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Data Sheet
29317.16E
2557
PROTECTED QUAD LOW-SIDE DRIVER
WITH FAULT DETECTION & SLEEP MODE
The A2557xB, A2557xEB, and A2557xLB have 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
A.
Over-current 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). Similar devices, for operation
to 1.3 A, are available as the UDx2547B/EB.
Continuous or multiple overload conditions causing the channel tempera-
ture 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 first character of the part number suffix determines the device
operating temperature range. Suffix `S-' is the standard -20
C to +85C;
suffix `E-' is -40
C to +85C; suffix `K-' is for the industrial temperature
range of -40
C to +125C. Package suffix `-B' devices are 16-pin power
DIPs; suffix `-EB' devices are 28-lead power PLCCs; and suffix `-LB' are 16-
lead power wide-body SOICs for surface-mount applications. All packages
are of batwing construction to provide for maximum package power dissipa-
tion.
FEATURES
I
300 mA Output Current per Channel
I
Independent Over-Current Protection &Thermal Limiting for Each Driver
I
Output Voltage to 60 V
I
Output SOA Protection
I
Fault-Detection Circuitry for Open or Shorted Load
I
Low Quiescent Current Sleep Mode
I
Integral Output Flyback/Clamp Diodes
I
TTL- and 5 V CMOS-Compatible Inputs
1
2
3
14
4
5
6
7
8
9
10
11
12
13
15
16
ENABLE
GROUND
GROUND
OUT
3
FAULT
GROUND
GROUND
OUT
2
OUT
1
K
OUT
4
V
CC
IN
4
Dwg. PP-017-4
IN
1
IN
2
IN
3
A2557xLB
Note that the A2557xB (DIP) and the A2557xLB
(SOIC) are electrically identical and share a
common terminal number assignment.
ABSOLUTE MAXIMUM RATINGS
Output Voltage, V
O
.............................. 60 V
Over-Current Protected Output Voltage,
V
O
..................................................... 32 V
Output Current, I
O
......................... 500 mA*
FAULT Output Voltage, V
FLT
............. 60 V
Logic Supply Voltage, V
CC
................. 7.0 V
Input Voltage, V
I
or V
OE
..................... 7.0 V
Package Power Dissipation,
P
D
........................................... See Graph
Operating Temperature Range, T
A
Suffix `S-' ...................... -20
C to +85
C
Suffix `E-' ...................... -40
C to +85
C
Suffix `K-' ................... -40
C to +125
C
Junction Temperature,
T
J
............................................... +150
C*
Storage Temperature Range,
T
S
................................. -55
C to +150
C
*Outputs are current limited at approximately
500 mA per driver and junction temperature
limited if higher current is attempted.
Complete part number includes a suffix to identify operating temperature
range (E-, K-, or S-) and package type (-B, -EB, or -LB). Always order by
complete part number, e.g., A2557KLB .
2557
PROTECTED QUAD DRIVER
WITH FAULT DETECTION
& SLEEP MODE
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
2
Copyright 1998, 2000, Allegro MicroSystems, Inc.
FUNCTIONAL BLOCK DIAGRAM
<<1
OUT
Dwg. FP-007-2
N
ENABLE
IN N
FAULT
COMMON CONTROL
ONE OF FOUR DRIVERS
CURRENT
LIMIT
THERMAL
LIMIT
SLEEP
CONTROL
30
A
60
A
2.5 V
+
K
V CC
A2557xEB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
GROUND
GROUND
GROUND
GROUND
Dwg. PP-019-2
NO
CONNECTION
ENABLE
SUPPLY
NC
NC
CC
V
OUT
1
OUT
2
OUT
3
OUT
4
IN
4
IN
3
IN
2
IN
1
NO
CONNECTION
K
FAULT
50
75
100
125
150
5
3
2
1
0
ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS
TEMPERATURE IN
C
4
25
R = 6
C/W
JT
Dwg. GP-004-2A
SUFFIX 'EB', R = 36
C/W
JA
SUFFIX 'B', R = 43
C/W
JA
SUFFIX 'LB', R = 63
C/W
JA
2557
PROTECTED QUAD DRIVER
WITH FAULT DETECTION
& SLEEP MODE
www.allegromicro.com
3
Limits
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Units
Output Leakage Current*
I
CEX
V
O
= 60 V, V
I
= 0.8 V, V
OE
= 2.0 V
--
30
100
A
V
O
= 60 V, V
I
= 2.0 V, V
OE
= 0.8 V
--
<1.0
100
A
Output Sustaining Voltage
V
O(SUS)
I
O
= 100 mA, V
I
= V
OE
= 0.8 V, V
CC
= Open
40
--
--
V
Output Saturation Voltage
V
O(SAT)
I
O
= 100 mA--
65
200
mV
I
O
= 300 mA--
180
300
mV
Over-Current Limit
I
OM
5 ms PulseTest, V
O
= 5.0 V
--
500
--
mA
Input Voltage
V
IH
IN
n
or ENABLE
2.0
--
--
V
V
IL
IN
n
or ENABLE
--
--
0.8
V
Input Current
I
IH
IN
n
or ENABLE, V
IH
= 2.0 V
--
--
10
A
I
IL
IN
n
or ENABLE, V
IL
= 0.8 V
--
--
-10
A
Fault Output Leakage Current
I
FLT
V
FLT
= 60 V
--
4.0
15
A
V
FLT
= 5 V
--
<1.0
2.0
A
Fault Output Current
I
FLT
V
FLT
=
5 V, Driver Output Open,
V
I
= 0.8 V, V
OE
= 2.0 V
40
60
80
A
Fault Output Saturation Voltage
V
FLT(SAT)
I
FLT
= 30
A--
0.1
0.4
V
Clamp Diode Forward Voltage
V
F
I
F
= 500 mA--
1.2
1.7
V
I
F
= 750 mA--
1.5
2.1
V
Clamp Diode Leakage Current
I
R
V
R
= 60 V
--
--
50
A
Turn-On Delay
t
PHL
I
O
= 300 mA, 50% V
I
to 50% V
O
--
0.6
10
s
From Sleep, I
O
= 300 mA, 50% V
I
to 50% V
O
--
3.0
--
s
I
O
= 300 mA, 50% V
OE
to 50% V
O
--
1.3
10
s
Turn-Off Delay
t
PLH
I
O
= 300 mA, 50% V
I
to 50% V
O
--
2.0
10
s
I
O
= 300 mA, 50% V
OE
to 50% V
O
--
1.4
10
s
Total Supply Current
I
CC
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
T
J
--
165
--
C
ELECTRICAL CHARACTERISTICS over operating temperature range, V
CC
= 4.75 V to 5.25 V
Typical Data is at T
A
= +25
C and V
CC
= 5 V and is for design information only.
Negative current is defined as coming out of (sourcing) the specified terminal.
As used here, -100 is defined as greater than +10 (absolute magnitude convention) and the minimum is implicitly zero.
* Measurement includes output fault-sensing pull-down current.
2557
PROTECTED QUAD DRIVER
WITH FAULT DETECTION
& SLEEP MODE
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
4
TYPICAL OPERATING CHARACTERISTICS
100
Dwg. GP-064
200
400
300
OUTPUT CURRENT IN MILLIAMPERES
0
0.3
0.2
OUTPUT SATURATION VOLTAGE IN VOLTS
0.1
0
V
CC
= 5 V
T
A
= 125
C
T
A
= 25
C
T
A
= -4
0C
10
Dwg. GP-065
20
40
30
OUTPUT VOLTAGE IN VOLTS
0
600
500
400
300
OUTPUT CURRENT LIMIT IN MILLIAMPERES
T
A
= +25
C
V
CC
= 5 V
100
Dwg. GP-066-1
200
400
300
OUTPUT CURRENT IN MILLIAMPERES
0
3
2
TURN-ON DELAY IN MICROSECONDS
1
0
T
A
= +25
C
V
CC
= 5 V
ENABLE SWITCHING
IN SWITCHING (FROM SLEEP)
IN SWITCHING (AWAKE)
100
Dwg. GP-066
200
400
300
OUTPUT CURRENT IN MILLIAMPERES
0
6
4
TURN-OFF DELAY IN MICROSECONDS
2
0
T
A
= +25
C
V
CC
= 5 V
ENABLE SWITCHING
IN S
WIT
CHIN
G
2557
PROTECTED QUAD DRIVER
WITH FAULT DETECTION
& SLEEP MODE
www.allegromicro.com
5
The A2557 low-current quad power drivers provide the
same protected output driver function as (and are pin compat-
ible with) the UDx2543/49/59 devices, combined with a fault
diagnostic scheme similar to the UDx2547, plus an automatic
low-current Sleep-Mode function. These devices 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 flagged by
pulling the common FAULT output low.
Status
IN
N
ENABLE
OUT
N
FAULT
Normal Load
H
H
L
H
L
H
H
H
Sleep Mode
X
L
H
H
All L
X
H
H
Over-Current or
Short to Supply
H
H
R
L
Open Load or
Short to Ground
L
H
L
L
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 OUT
n
terminal
using a comparator whose threshold is typically 2.5 V. In order
to detect open-circuit outputs, a 30
A 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
A output sinks are turned off.
The FAULT output is a switched current sink of typically
60
A.
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 detecting 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
output current limit is further reduced
CIRCUIT DESCRIPTION AND APPLICATION
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 tempera-
ture). As each channel has its own thermal limit circuitry this
provides some independence between the output channels, i.e.,
one channel 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 V
O
= 8 V;
above this the limit is reduced linearly to about 350 mA at V
O
=
32 V. This helps to improve SOA by immediately reducing the
peak power pulse into a shorted load at high V
O
.
A logic low at the ENABLE input causes all outputs to be
switched off regardless of the state of the IN terminals. In
addition, the device is put into a low quiescent current `sleep'
mode, reducing I
CC
below 100
A. 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 flyback 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 filament 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 significant 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 filament resistance increases to its maximum
value, the output driver goes into saturation and applies maxi-
mum rated voltage to the lamp.