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AOUT (DFN and SO Packages Only): Amplifier Output.
Open collector output of the auxiliary amplifier. It is capable
of sinking up to 2mA from 80V. The negative input of the
amplifier is internally connected to a 1.25V reference.
EN: Open-Collector Enable Output. The EN pin goes high
impedance when the voltage at the OUT pin is above (VCC
– 0.7V), indicating the external MOSFET is fully on. The
state of the pin is latched until the OUT pin voltage resets
at below 0.5V and goes back up above 2V. The internal
NPN is capable of sinking up to 3mA of current from 80V
to drive an LED or opto-coupler.
Exposed Pad (DFN Package Only): Exposed pad may be
left open or connected to device ground (GND).
FB: Voltage Regulator Feedback Input. Connect this pin
to the center tap of the output resistive divider connected
between the OUT pin and ground. During an overvoltage
condition, the GATE pin is servoed to maintain a 1.25V
threshold at the FB pin. This pin is clamped internally to
7V. Tie to GND to disable the OV clamp.
FLT: Open-Collector Fault Output. This pin pulls low
after the voltage at the TMR pin has reached the fault
threshold of 1.25V. It indicates the pass transistor is
about to turn off because either the supply voltage has
stayed at an elevated level for an extended period of
time (voltage fault) or the device is in an overcurrent
condition (current fault). The internal NPN is capable of
sinking up to 3mA of current from 80V to drive an LED or
GATE: N-Channel MOSFET Gate Drive Output. The GATE pin
is pulled up by an internal charge pump current source and
clamped to 14V above the OUT pin. Both voltage and cur-
rent amplifiers control the GATE pin to regulate the output
voltage and limit the current through the MOSFET.
GND: Device Ground.
IN+ (DFN and SO Packages Only): Positive Input of the
Auxiliary Amplifier. This amplifier can be used as a level
detection comparator with external hysteresis or linear
regulator controlling an external PNP transistor. This pin is
clamped internally to 7V. Connect to ground if unused.
OUT: Output Voltage Sense Input. This pin senses the
voltage at the source of the N-channel MOSFET and sets
the fault timer current. When the OUT pin voltage reaches
0.7V away from VCC, the EN pin goes high impedance.
SHDN: Shutdown Control Input. The LT4356 can be shut
down to a low current mode by pulling the SHDN pin below
0.4V. Pull this pin above 2.1V or disconnect it and allow
the internal current source to turn the part back on. The
leakage current to ground at the pin should be limited to
no more than 1µA if no pull up device is used to turn the
part on. The SHDN pin can be pulled up to 100V or below
GND by 60V without damage. In shutdown, the auxiliary
amplifier turns off in the LT4356-1 but continues operating
in the LT4356-2.
SNS: Current Sense Input. Connect this pin to the output of
the current sense resistor. The current limit circuit controls
the GATE pin to limit the sense voltage between VCC and
SNS pins to 50mV. At the same time the sense amplifier
also starts a current source to charge up the TMR pin.
This pin can be pulled below GND by up to 60V, though
the voltage difference with the VCC pin must be limited to
less than 30V. Connect to VCC if unused.
TMR: Fault Timer Input. Connect a capacitor between this
pin and ground to set the times for early warning, fault
and cool down periods. The current charging up this pin
during fault conditions depends on the voltage difference
between the VCC and OUT pins. When VTMR reaches 1.25V,
the F LT pin pulls low to indicate the detection of a fault
condition. If the condition persists, the pass transistor turns
off when VTMR reaches the threshold of 1.35V. As soon as
the fault condition disappears, the pull up current stops
and a 2µA current starts to pull the TMR pin down. When
VTMR reaches the retry threshold of 0.5V, the GATE pin pulls
high turning back on the pass transistor. A minimum of
10nF capacitor is needed to compensate the loop. A 10V
rated X7R capacitor is recommended for CTMR.
VCC: Positive Supply Voltage Input. The positive supply
input ranges from 4V to 80V for normal operation. It
can also be pulled below ground potential by up to 60V
during a reverse battery condition, without damaging the
part. The supply current is reduced to 7µA with all the
functional blocks off.