LT4356HMS-3#PBF Linear Technology, LT4356HMS-3#PBF Datasheet - Page 9

• Manufacturer Part Number: LT4356HMS-3#PBF
• Description: IC, SURGE STOPPER, 16V, MSOP-10
• Manufacturer: Linear Technology

Specifications of LT4356HMS-3#PBF

• Input Voltage: 1.25V
• Internal Switch: No
• Supply Voltage Range: 4V To 80V
• Digital Ic Case Style: MSOP
• No. Of Pins: 10
• Operating Temperature Range: -40°C To +125°C
• Peak Reflow Compatible (260 C): Yes
• Msl: MSL 1 - Unlimited
• Rohs Compliant: Yes
• Applications: Automotive/Avionic Surge Protection, Intrinsic Safety Applications, High Side Switch
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

OPERATION
Some power systems must cope with high voltage surges
of short duration such as those in automobiles. Load
circuitry must be protected from these transients, yet
high availability systems must continue operating during
these events.
The LT4356-3 is an overvoltage protection regulator that
drives an external N-channel MOSFET as the pass transis-
tor. It operates from a wide supply voltage range of 4V to
80V. It can also be pulled below ground potential by up
to 60V without damage. The low power supply require-
ment of 4V allows it to operate even during cold cranking
conditions in automotive applications. The internal charge
pump turns on the N-channel MOSFET to supply current
to the loads with very little power loss. Two MOSFETs can
be connected back to back to replace an inline Schottky
diode for reverse input protection. This improves the ef-
fi ciency and increases the available supply voltage level
to the load circuitry during cold crank.
Normally, the pass transistor is fully on, powering the
loads with very little voltage drop. When the supply volt-
age surges too high, the voltage amplifi er (VA) controls
the gate of the MOSFET and regulates the voltage at the
source pin to a level that is set by the external resistive
divider from the OUT pin to ground and the internal 1.25V
reference. A current source starts charging up the capaci-
tor connected at the TMR pin to ground. If the voltage at
the TMR pin, V
to indicate impending turn-off due to the overvoltage
condition. The pass transistor stays on until the TMR
pin reaches 1.35V, at which point the GATE pin pulls low
turning off the MOSFET.
TMR
, reaches 1.25V, the FLT pin pulls low
The potential at the TMR pin starts decreasing as soon
as the overvoltage condition disappears, but the GATE
pin remains low even when the voltage at the TMR pin
reaches 0.5V. Pulling the SHDN pin low momentarily will
turn the GATE pin back on.
The fault timer allows the load to continue functioning
during short transient events while protecting the MOSFET
from being damaged by a long period of supply overvoltage,
such as a load dump in automobiles. The timer period var-
ies with the voltage across the MOSFET. A higher voltage
corresponds to a shorter fault timer period, ensuring the
MOSFET operates within its safe operating area (SOA).
The LT4356-3 senses an overcurrent condition by monitor-
ing the voltage across an optional sense resistor placed
between the V
circuit (IA) controls the GATE pin to limit the sense volt-
age to 50mV. A current is also generated to start charging
up the TMR pin. This current is about 5 times the current
generated during an overvoltage event. The FLT pin pulls
low when the voltage at the TMR pin reaches 1.25V and
the MOSFET is turned off when it reaches 1.35V.
An auxiliary amplifi er is provided with the negative input
connected to an internal 1.25V reference. The output pull
down device is capable of sinking up to 2mA of current
allowing it to drive an LED or opto coupler. This amplifi er
can be confi gured as a linear regulator controller driving
an external PNP transistor or a comparator function to
monitor voltages.
The SHDN pin turns off the pass transistor and reduces
the supply current to less than 7μA.
CC
and SNS pins. An active current limit
LT4356-3
43563fa
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