LTC1154

6

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BLOCK DIAGRAM

PIN FUNCTIONS

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.

Supply Pin

The supply pin of the LTC1154 serves two vital purposes.

The first is obvious: it powers the input, gate drive, regula-

tion 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.

Drain Sense Pin

The drain sense pin is compared 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

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

DRAIN

SENSE

ONE

SHOT

TTL-TO-CMOS

CONVERTER

VOLTAGE

REGULATORS

ANALOG

DIGITAL

GND

LOW STANDBY

CURRENT

REGULATOR

INPUT

STATUS

10μs

DELAY

LTC1154 • BD01

ENABLE

COMP