LT4363
8
4363fb
For more information
pin FuncTions
ENOUT:
Open Collector Enable Output. The ENOUT pin goes
high impedance when the voltage at the OUT pin is within
0.5V of V
CC
and 3V above GND, indicating the external
MOSFET is fully on. The state of the pin is latched until the
OUT pin voltage drops below 2V, resetting the latch. The
internal NPN is capable of sinking up to 2mA of current.
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 resistive divider connected between
the OUT pin and ground. During an overvoltage condition,
the GATE pin is controlled to maintain a 1.275V threshold
at the FB pin. Connect 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 1.275V. 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 2mA of current.
GATE:
N-Channel MOSFET Gate Drive Output. The GATE pin
is pulled up by an internal charge pump current source to
13V above the OUT pin. A 14V protection clamp limits this
voltage during faults. Both voltage and current amplifiers
control the GATE pin to regulate the output voltage and
limit the current through the MOSFET.
GND:
Device Ground.
OUT:
Output Voltage Sense Input. This pin senses the
voltage at the source of the external N-channel MOSFET.
The voltage difference between V
CC
and OUT sets the fault
timer current. When this difference drops below 0.5V, the
EN pin goes high impedance.
OV (LT4363-2):
Overvoltage Comparator Input. When OV
is above its threshold of 1.275V, the fault retry function
is inhibited even when the TMR pin voltage has reached
its retry threshold. As soon as the voltage at OV pin falls
below its lower threshold the GATE pin is allowed to turn
back on. Connect to GND if unused.
SHDN:
Shutdown Control Input. The LT4363 can be
shutdown to a low current mode by pulling the
SHDN
pin
below the threshold of 0.4V. Pull this pin above 2.1V or
disconnect it to 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 external
pull up is used to turn the part on. The
SHDN
pin can be
pulled up to 100V or below GND by 60V without damage.
SNS:
Current Sense Input. Connect this pin to the input of
the current sense resistor. The current limit circuit controls
the GATE pin to limit the sense voltage between SNS and
OUT pins to 50mV. This is reduced to 25mV in a severe
fault when OUT is below 2V. When in current limit mode,
a current source charges up the TMR pin. The voltage
difference with the OUT pin must be limited to less than
30V. Connect to OUT pin if unused.
TMR:
Fault Timer Input. Connect a capacitor between this
pin and ground to set the times for early fault warning,
fault turn-off, and cool down periods. The current charg-
ing up this pin during fault conditions depends on the
voltage difference between the V
CC
and OUT pins. When
TMR reaches 1.275V, the
FLT
pin pulls low to indicate the
detection of a fault condition. If the condition persists, the
pass transistor turns off when TMR reaches the threshold
of 1.375V. A 2µA current source then continues to pull the
TMR up. When TMR reaches 4.3V, the 2µA current reverses
direction and starts to pull the TMR pin low. When TMR
reaches the retry threshold of 0.5V, the GATE pin pulls
high turning back on the pass transistor for the LT4363-2
version. The GATE pin latches low after fault time out for
the LT4363-1. A minimum of 10nF capacitor is needed to
compensate the loop.
UV:
Undervoltage Comparator Input. When UV falls below
its threshold of 1.275V, the GATE is pulled down with a
1mA current. When UV rises above 1.275V plus the hys-
teresis, the pull down current disappears and the GATE
pin is pulled up by the internal charge pump. If unused,
connect to V
CC
.
V
CC
:
Positive Supply Voltage Input. The positive supply
input ranges from 4V to 80V for normal operation. It can
also be pulled below ground by up to 60V during a reverse
battery condition, without damaging the part. Shutting
down the LT4363 by pulling the
SHDN
pin to ground will
reduce the supply current to 7µA.
