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PDF LT4356-2 Data sheet ( Hoja de datos )
| Número de pieza | LT4356-2 | |
| Descripción | Surge Stopper | |
| Fabricantes | Intersil Corporation | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LT4356-2 (archivo pdf) en la parte inferior de esta página. Total 24 Páginas | ||
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FEATURES
n Stops High Voltage Surges
n Adjustable Output Clamp Voltage
n Overcurrent Protection
n Wide Operation Range: 4V to 80V
n Reverse Input Protection to –60V
n Low 7μA Shutdown Current, LT4356-1
n Adjustable Fault Timer
n Controls N-channel MOSFET
n Shutdown Pin Withstands –60V to 100V
n Fault Output Indication
n Guaranteed Operation to 125°C
n Spare Amplifier for Level Detection Comparator or
Linear Regulator Controller
n Available in (4mm × 3mm) 12-Pin DFN,
10-Pin MSOP or 16-Pin SO Packages
APPLICATIONS
n Automotive/Avionic Surge Protection
n Hot Swap/Live Insertion
n High Side Switch for Battery Powered Systems
n Intrinsic Safety Applications
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
LT4356-1/LT4356-2
Surge Stopper
DESCRIPTION
The LT®4356 surge stopper protects loads from high voltage
transients. It regulates the output during an overvoltage
event, such as load dump in automobiles, by controlling
the gate of an external N-channel MOSFET. The output is
limited to a safe value thereby allowing the loads to con-
tinue functioning. The LT4356 also monitors the voltage
drop between the VCC and SNS pins to protect against
overcurrent faults. An internal amplifier limits the current
sense voltage to 50mV. In either fault condition, a timer
is started inversely proportional to MOSFET stress. If the
timer expires, the FLT pin pulls low to warn of an impend-
ing power down. If the condition persists, the MOSFET is
turned off. After a cool down period, the GATE pin pulls
up turning on the MOSFET again.
The spare amplifier may be used as a voltage detection
comparator or as a linear regulator controller driving an
external PNP pass transistor.
Back-to-back FETs can be used in lieu of a Schottky diode
for reverse input protection, reducing voltage drop and
power loss. A shutdown pin reduces the quiescent current
to less than 7μA during shutdown for the LT4356-1 and
60μA for the LT4356-2 while keeping the reference and
auxiliary amplifier functioning.
TYPICAL APPLICATION
4A, 12V Overvoltage Output Regulator
VIN
10mΩ IRLR2908
VOUT
12V
383k
100k
UNDERVOLTAGE
10Ω
VCC
SHDN
IN+
SNS GATE OUT
FB
LT4356DE
AOUT
GND
EN
TMR FLT
4356 TA01
0.1μF
102k
4.99k
VCC
DC-DC
CONVERTER
SHDN GND
FAULT
Overvoltage Protector Regulates Output at
27V During Transient
80V INPUT SURGE
CTMR = 6.8μF
ILOAD = 500mA
VIN
20V/DIV
12V
VOUT
20V/DIV
12V
27V ADJUSTABLE CLAMP
100ms/DIV
4356 TA01b
4356f
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LT4356-1/LT4356-2
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 12V unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN TYP MAX
VSHDN(FLT) SHDN Pin Float Voltage
ISHDN
SHDN Pin Current
VCC = 12V to 48V
VSHDN = 0V
l 0.6
1.2
2
l –1 –4 –8
tOFF(OC) Overcurrent Turn Off Delay Time GATE From High to Low, ΔVSNS = 0 → 120mV
l
24
tOFF(OV) Overvoltage Turn Off Delay Time GATE From High to Low, VFB = 0 → 1.5V
l 0.25 1
UNITS
V
μA
μs
μs
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to GND unless otherwise
specified.
Note 3: An internal clamp limits the GATE pin to a minimum of 10V above
the OUT pin. Driving this pin to voltages beyond the clamp may damage
the device.
TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at VCC = 12V, TA = 25°C unless otherwise noted.
ICC vs VCC
1000
800
600
400
200
0
0 10 20 30 40 50 60 70 80
VCC (V)
4356 G02
ICC (Shutdown) vs VCC
60 LT4356-1
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80
VCC (V)
4356 G01
ICC (Shutdown) vs VCC
120 LT4356-2
IN+ = 1.3V
100
80
60
40
20
0
0 10 20 30 40 50 60 70 80
VCC (V)
4356 G20
ICC (Shutdown) vs Temperature
35 LT4356-1
30
25
20
15
10
5
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
4356 G03
ICC (Shutdown) vs Temperature
300 LT4356-2
250
200
150
100
50
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
4356 G21
4356f
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LT4356-1/LT4356-2
APPLICATIONS INFORMATION
The LT4356 can limit the voltage and current to the load
circuitry during supply transients or overcurrent events.
The total fault timer period should be set to ride through
short overvoltage transients while not causing damage
to the pass transistor. The selection of this N-channel
MOSFET pass transistor is critical for this application.
It must stay on and provide a low impedance path from
the input supply to the load during normal operation and
then dissipate power during overvoltage or overcurrent
conditions.
The following sections describe the overcurrent and the
overvoltage faults, and the selection of the timer capacitor
value based on the required warning time. The selection
of the N-channel MOSFET pass transistor is discussed
next. Auxiliary amplifier, reverse input, and the shutdown
functions are covered after the MOSFET selection. External
component selection is discussed in detail in the Design
Example section.
Overvoltage Fault
The LTC4356 limits the voltage at the OUT pin during an
overvoltage situation. An internal voltage amplifier regu-
lates the GATE pin voltage to maintain a 1.25V threshold at
the FB pin. During this period of time, the power MOSFET
is still on and continues to supply current to the load. This
allows uninterrupted operation during short overvoltage
transient events.
When the voltage regulation loop is engaged for longer
than the time-out period, set by the timer capacitor con-
nected from the TMR pin to ground, an overvoltage fault is
detected. The GATE pin is pulled down to the OUT pin by a
150mA current. After the fault condition has disappeared
and a cool down period has transpired, the GATE pin starts
to pull high again. This prevents the power MOSFET from
being damaged during a long period of overvoltage, such
as during load dump in automobiles.
Overcurrent Fault
The LT4356 features an adjustable current limit that
protects against short circuits or excessive load current.
During an overcurrent event, the GATE pin is regulated to
limit the current sense voltage across the VCC and SNS
pins to 50mV.
An overcurrent fault occurs when the current limit circuitry
has been engaged for longer than the time-out delay set
by the timer capacitor. The GATE pin is then immediately
pulled low by a 10mA current to GND turning off the
MOSFET. After the fault condition has disappeared and a
cool down period has transpired, the GATE pin is allowed
to pull back up and turn on the pass transistor.
Fault Timer
The LT4356 includes an adjustable fault timer pin. Con-
necting a capacitor from the TMR pin to ground sets the
delay timer period before the MOSFET is turned off. The
same capacitor also sets the cool down period before the
MOSFET is allowed to turn back on after the fault condition
has disappeared.
Once a fault condition, either overvoltage or overcurrent,
is detected, a current source charges up the TMR pin. The
current level varies depending on the voltage drop across
the drain and source terminals of the power MOSFET(VDS),
which is typically from the VCC pin to the OUT pin. This
scheme takes better advantage of the available Safe
Operating Area (SOA) of the MOSFET than would a fixed
timer current. The timer function operates down to VCC =
5V across the whole temperature range.
4356f
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11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT4356-2.PDF ] | |
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