A2557EEB Allegro Microsystems Inc, A2557EEB Datasheet - Page 7

• Manufacturer Part Number: A2557EEB
• Description: IC DRIVER QUAD 60V 300MA 28-PLCC
• Manufacturer: Allegro Microsystems Inc
• Type: Low Sider

Specifications of A2557EEB

• Number Of Outputs: 4
• Input Type: Non-Inverting
• Current - Output / Channel: 300mA
• Current - Peak Output: 500mA
• Voltage - Supply: 4.75 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-LCC (J-Lead)
• Switch Type: Low Side
• Power Switch Family: A2557
• Input Voltage: 7V
• Output Current: 300mA
• Mounting: Surface Mount
• Supply Current: 30mA
• Package Type: PLCC
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Pin Count: 28
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• On-state Resistance: -
• Lead Free Status / RoHS Status: Not Compliant, Contains lead / RoHS non-compliant

A2557
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.
The FAULT output is operational only if ENABLE is high. The
output state is detected by monitoring the OUT
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:
•
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
R = Linear drive, current limited.
if the power dissipation in the output device increases the
Short to Ground
Over-Current or
Short to Supply
Open Load or
Thermal Fault
Normal Load
Sleep Mode
Status
All L
IN
H
H
H
X
L
L
N
CIRCUIT DESCRIPTION AND APPLICATION
ENABLE
H
H
H
H
H
X
L
n
OUT
terminal using a
H
H
H
R
H
L
L
N
FAULT
H
H
H
H
L
L
L
with Fault Detection and Sleep Mode
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.
•
500 mA (nominal) is available up to approximately V
above this the limit is reduced linearly to about 350 mA at V
32 V. This helps to improve SOA by immediately reducing the
peak power pulse into a shorted load at high V
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 I
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.
as a function of the output voltage. Full current limit of
CC
below 100 μA. If ENABLE is taken high and any
Protected Quad Driver
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
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= 8 V;
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