LTC1154
6
1154fc
For more information www.linear.com/LTC1154
block DiagraM
pin FuncTions
G (Pin 6): Gate Drive Pin. The gate drive pin is either driven
to ground when the switch is turned OFF or driven above
the supply rail when the switch is turned ON. This pin is a
relatively high impedance when driven above the rail (the
equivalent of a few hundred kΩ). Care should be taken to
minimize any loading of this pin by parasitic resistance
to ground or supply.
V
S
(Pin 8): Supply Pin. The supply pin of the LTC1154
serves two vital purposes. The first is obvious: it powers
the input, gate drive, regulation and protection circuitry.
The second purpose is less obvious: it provides a Kelvin
connection to the top of the drain sense resistor for the
internal 100mV reference.
The LTC1154 is designed to be continuously powered so
that the gate of the MOSFET is actively driven at all times.
If it is necessary to remove power from the supply pin
and then re-apply it, the input pin (or enable pin) should
be cycled a few milliseconds after the power is re-applied
to reset the input latch and protection circuitry. Also, the
input and enable pins should be isolated with 10k resistors
to limit the current flowing through the ESD protection
diodes to the supply pin.
The supply pin of the LTC1154 should never be forced
below ground as this may result in permanent damage to
the device. A 300Ω resistor should be inserted in series
with the ground pin if negative supply voltage transients
are anticipated.
DS (Pin 7): Drain Sense Pin. The drain sense pin is com
-
pared against the supply pin voltage. If the voltage at this
pin is more than 100mV below the supply pin, the input
latch will be reset and the MOSFET gate will be quickly
discharged. Cycle the input, or ENABLE input, to reset the
short-circuit latch and turn the MOSFET back on.
This pin is also a high impedance CMOS gate with ESD
protection and therefore should not be forced beyond the
power supply rails. To defeat the overcurrent protection,
short the drain sense to supply.
Some loads, such as large supply capacitors, lamps, or
motors require high inrush currents. An RC time delay
can be added between the sense resistor and the drain
sense pin to ensure that the drain sense circuitry does not
false-trigger during start-up. This time constant can be
set from a few microseconds to many seconds. However,
very long delays may put the MOSFET in risk of being
destroyed by a short-circuit condition. (see Applications
Information Section).
STATUS (Pin 3): STATUS Pin. The STATUS pin is an open-
drain output which is driven low whenever a fault condition
is detected. A 51k pull-up resistor should be connected
between this output and a logic supply. The STATUS pins
of multiple LTC1154s can be OR’d together if independent
fault sensing is not required. No connection is required to
this pin when not in use.
GATE CHARGE
AND DISCHARGE
CONTROL LOGIC
SHUTDOWN
TTL-TO-CMOS
CONVERTER
OSCILLATOR
AND CHARGE
PUMP
FAST/SLOW
GATE CHARGE
LOGIC
FAULT DETECTION
AND STATUS
OUTPUT DRIVER
100mV
REFERENCE
ANALOG SECTION
INPUT
LATCH
R
S
GATE
SHUTDOWN
SENSE
ONE
SHOT
TTL-TO-CMOS
CONVERTER
VOLTAGE
REGULATORS
ANALOG DIGITAL
GND
LOW STANDBY
CURRENT
REGULATOR
INPUT
STATUS
V
S
10µs
DELAY
LTC1154 • BD01
ENABLE
COMP
