A2557: Protected Quad Driver with Fault Detection and Sleep Mode

A2557
Protected Quad Driver with Fault Detection and Sleep Mode
Last Time Buy
These parts are in production but have been determined to be
LAST TIME BUY. This classification indicates that the product is
obsolete and notice has been given. Sale of this device is currently
restricted to existing customer applications. The device should not be
purchased for new design applications because of obsolescence in the
near future. Samples are no longer available.
Date of status change: November 1, 2010
Deadline for receipt of LAST TIME BUY orders: April 30, 2011
Recommended Substitutions:
For existing customer transition, and for new customers or new applications, contact Allegro Sales.
NOTE: For detailed information on purchasing options, contact your
local Allegro field applications engineer or sales representative.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, revisions to the anticipated product life cycle plan
for a product to accommodate changes in production capabilities, alternative product availabilities, or market demand. The
information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use.
A2557
Protected Quad Driver
with Fault Detection and Sleep Mode
Features and Benefits
Description
▪ 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
The A2557 has been specifically designed to provide costeffective solutions to relay-driving applications with up to 300
mA drive current per channel. It 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.
Package: 16-pin SOICW with internally
fused pins (LB)
Not to scale
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).
Continued on the next page…
Functional Block Diagram
FAULT
ENABLE
SLEEP
CONTROL
60 A
K
COMMON CONTROL
ONE OF FOUR DRIVERS
V CC
–
2.5 V
+
OUTN
IN N
THERMAL
LIMIT
CURRENT
LIMIT
30 A
<<1
29317.16N
Protected Quad Driver
with Fault Detection and Sleep Mode
A2557
Description (continued)
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 package offers fused leads for enhanced thermal dissipation.
Package LB is a 16-lead power wide SOIC for surface-mount
applications. It is lead (Pb) free, with 100% matte tin leadframe
plating.
Selection Guide
Part Number
A2557KLBTR-T
Package
16-lead SOIC
Packing
1000 pieces per reel
Ambient Temperature
(°C)
–40 to 125
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
Protected Quad Driver
with Fault Detection and Sleep Mode
A2557
Absolute Maximum Ratings
Characteristic
Symbol
Logic Supply Voltage
Input Voltage
Output Voltage
Overcurrent Protected Output Voltage
Output Current
7.0
V
7.0
V
VO
60
V
VO(OCP)
32
V
500
mA
60
V
–
–
Outputs current-limited to approximately 500 mA
per driver, and TJ limited if higher current is
attempted
VFLT
PD
Operating Ambient Temperature
TA
Maximum Junction Temperature
TJ(max)
Tstg
ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS
Units
VCC
Package Power Dissipation
Storage Temperature
Rating
VI or VOE
IO
FAULT Output Voltage
Notes
See graph
Range E
–40 to 85
ºC
Range K
–40 to 125
ºC
Range S
–20 to 85
ºC
150
ºC
–55 to 150
ºC
2
1
SUFFIX 'LB', R JA = 90 C/W
0
25
50
75
100
TEMPERATURE IN C
125
150
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
Protected Quad Driver
with Fault Detection and Sleep Mode
A2557
Pin-out Diagram
LB Package
OUT1
1
16
IN 1
K
2
15
IN2
OUT2
3
14
ENABLE
GROUND
4
13
GROUND
GROUND
5
12
GROUND
OUT3
6
11
V CC
FAULT
7
10
IN 3
8
9
IN 4
OUT4
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Copyright © 1998, 2002 Allegro MicroSystems, Inc.
4
Protected Quad Driver
with Fault Detection and Sleep Mode
A2557
ELECTRICAL CHARACTERISTICS over operating temperature range, VCC = 4.75 V to 5.25 V
Characteristic
Output Leakage Current*
Symbol
ICEX
Test Conditions
Min.
Limits
Typ. Max.
Units
VO = 60 V, VI = 0.8 V, VOE = 2.0 V
—
30
100
μA
VO = 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)
IO = 100 mA
—
65
200
mV
IO = 300 mA
—
180
300
mV
5 ms PulseTest, VO = 5.0 V
—
500
—
mA
Over-Current Limit
IOM
Input Voltage
VIH
INn or ENABLE
2.0
—
—
V
VIL
INn or ENABLE
—
—
0.8
V
IIH
INn or ENABLE, VIH = 2.0 V
—
—
10
μA
IIL
INn or ENABLE, VIL = 0.8 V
—
—
-10
μA
VFLT = 60 V
—
4.0
15
μA
VFLT = 5 V
—
<1.0
2.0
μA
VFLT = 5 V, Driver Output Open,
VI = 0.8 V, VOE = 2.0 V
40
60
80
μA
VFLT(SAT)
IFLT = 30 μA
—
0.1
0.4
V
Clamp Diode Forward Voltage
VF
IF = 500 mA
—
1.2
1.7
V
IF = 750 mA
—
1.5
2.1
V
Clamp Diode Leakage Current
IR
VR = 60 V
—
—
50
μA
IO = 300 mA, 50% VI to 50% VO
—
0.6
10
μs
From Sleep, IO = 300 mA, 50% VI to 50% VO
—
3.0
—
μs
Input Current
Fault Output Leakage Current
Fault Output Current
Fault Output Saturation Voltage
Turn-On Delay
Turn-Off Delay
Total Supply Current
Thermal Limit
IFLT
IFLT
tPHL
tPLH
ICC
TJ
IO = 300 mA, 50% VOE to 50% VO
—
1.3
10
μs
IO = 300 mA, 50% VI to 50% VO
—
2.0
10
μs
IO = 300 mA, 50% VOE to 50% VO
—
1.4
10
μs
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
—
165
—
°C
Typical Data is at TA = +25°C and VCC = 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.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
Protected Quad Driver
with Fault Detection and Sleep Mode
A2557
TYPICAL OPERATING CHARACTERISTICS
0.3
VCC = 5 V
OUTPUT CURRENT LIMIT IN MILLIAMPERES
OUTPUT SATURATION VOLTAGE IN VOLTS
600
oC
5
0.2
T
A
=
12
5 oC
TA
=2
oC
40
=-
TA
0.1
0
0
100
200
300
T A = +25oC
VCC = 5 V
500
400
300
400
0
OUTPUT CURRENT IN MILLIAMPERES
10
20
40
30
OUTPUT VOLTAGE IN VOLTS
Dwg. GP-064
Dwg. GP-065
T A = +25oC
VCC = 5 V
4
IN S
WIT
ENA
2
0
BLE
0
100
200
CH
SW
ING
ITC
HIN
G
300
IN SWITCHING (FROM SLEEP)
3
TURN-ON DELAY IN MICROSECONDS
TURN-OFF DELAY IN MICROSECONDS
6
400
OUTPUT CURRENT IN MILLIAMPERES
Dwg. GP-066
T A = +25oC
VCC = 5 V
2
ENABLE SWITCHING
1
IN SWITCHING (AWAKE)
0
0
100
200
400
300
OUTPUT CURRENT IN MILLIAMPERES
Dwg. GP-066-1
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
Protected Quad Driver
with Fault Detection and Sleep Mode
A2557
CIRCUIT DESCRIPTION AND APPLICATION
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 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
Normal Load
Sleep Mode
INN
ENABLE
OUTN
FAULT
H
H
L
H
L
H
H
H
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 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 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:
• 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 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 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 addition, 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 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 maximum rated
voltage to the lamp.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
Protected Quad Driver
with Fault Detection and Sleep Mode
A2557
CIRCUIT DESCRIPTION AND APPLICATION (continued)
NORMAL LAMP IN-RUSH CURRENT
Fault diagnostics
A pull-up resistor or current source is required on the FAULT
output. This can be connected to whatever supply level the following circuitry requires (within the specification 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 following the combined duty-cycle of all channels showing a fault
condition. There are therefore two basic approaches to using the
function in an application:
LAMP CURRENT
NOT TO SCALE
THERMAL GRADIENT SENSING
CURRENT LIMIT
ITRIP
0
TIME
Dwg. WP-008
Inductive load driver
Bifilar (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 flyback voltage and improve performance. However, the
peak voltage must not exceed the specified 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 thermalshutdown circuit will shut off the affected output. If the fault
condition is corrected, the output driver will return to its normal
saturated condition.
• 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 find 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’ channels while disabling signals to the faulty channel.
• As a simple ‘common’ fault indication. If there is no controller 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 reflect 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.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
Protected Quad Driver
with Fault Detection and Sleep Mode
A2557
CIRCUIT DESCRIPTION AND APPLICATION (continued)
OUTPUT CURRENT
NOT TO SCALE
IN
FAULT
(SHORTED
LOAD)
SHORT CIRCUIT
NORMAL LOAD
WITH OUTPUT CAPACITOR
CURRENT LIMIT (12 V SUPPLY)
FAULT
(OPEN
LOAD)
CURRENT LIMIT (24 V SUPPLY)
Dwg. WP-035
TIME
Dwg. WP-013-1
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 turnoff delay (see characteristics above) of the output stage increases
and may result in a spurious fault output of a few μs (the duration being proportional to the turn-off delay). As it is difficult to
define this over all operating conditions, if a particular application 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 filament results in the driver operating in current
limit for a period after turn-on. During this period a “fault” condition 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 microcontrollerbased system, the code could be written to ignore the FAULT
condition for an appropriate period after lamp turn on.
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 reasonable 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 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.
Correct FAULT operation cannot be guaranteed with an unconnected output — unused outputs should not be turned on, or
unused outputs should be pulled high to >2.5 V, and/or associated inputs tied low.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
9
Protected Quad Driver
with Fault Detection and Sleep Mode
A2557
LB Package, 16-pin SOIC
with internally fused pins 4 and 5, and 12 and 13
10.30±0.20
4° ±4
16
1.27
0.65
16
+0.07
0.27 –0.06
10.30±0.33
7.50±0.10
9.50
A
+0.44
0.84 –0.43
2.25
1
2
1
0.25
16X
SEATING
PLANE
0.10 C
0.41 ±0.10
1.27
C
2
B
PCB Layout Reference View
SEATING PLANE
GAUGE PLANE
2.65 MAX
0.20 ±0.10
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
A Terminal #1 mark area
B
Reference 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
Copyright ©1998-2010, Allegro MicroSystems, Inc.
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 departures from the detail specifications as may be required to permit improvements in the performance, 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 information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use;
nor for any infringement of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
10
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