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LTC1154

The LTC1154 is a single micropower MOSFET driver with

built-in protection, status feedback and gate charge pump.

The LTC1154 consists of the following functional blocks:

TTL and CMOS Compatible Inputs

The LTC1154 input and shutdown input have been de-

signed to accommodate a wide range of logic families.

Both input thresholds are set at about 1.3V with approxi-

mately 100mV of hysteresis.

A low standby current voltage regulator provides continu-

ous bias for the TTL-to-CMOS converter. The TTL-to-

CMOS converter output enables the rest of the circuitry. In

this way the power consumption is kept to a minimum in

the standby mode.

ENABLE Input

The ENABLE input is CMOS compatible and inhibits the

input signal whenever it is held logic high. This input

should be grounded when not in use.

Internal Voltage Regulation

The output of the TTL-to-CMOS converter drives two

regulated supplies which power the low voltage CMOS

logic and analog blocks. The regulator outputs are isolated

from each other so that the noise generated by the charge

TRUTH TABLE

The Truth Table demonstrates how the LTC1154 receives

inputs and returns status information to the

µP. The

ENABLE and input signal from the

µP controls the switch

in its normal operating mode, where the rise and fall time

of the gate drive are controlled to limit EMI and RFI

emissions. The shutdown and over-current detection cir-

cuitry however, switch the gate off at a much higher rate

to limit the exposure of the MOSFET switch and the load to

dangerous conditions. The status pin remains high as long

as the switch is operating normally, and is driven low only

when a fault condition is detected. Note that the shutdown

pin is edge-sensitive and latches the output off even if the

shutdown pin returns to a low state.

LTC1154 OPERATIO

pump logic is not coupled into the 100mV reference or the

analog comparator.

Gate Charge Pump

Gate drive for the MOSFET switch is produced by an

adaptive charge pump circuit which generates a gate

voltage substantially higher than the power supply volt-

age. The charge pump capacitors are included on chip and

therefore no external components are required to generate

the gate drive.

Drain Current Sense

The LTC1154 is configured to sense the current flowing

into the drain of the power MOSFET in a high-side applica-

tion. An internal 100mV reference is compared to the drop

across a sense resistor (typically 0.002

Ω to 0.10Ω) in

series with the drain lead. If the drop across this resistor

exceeds the internal 100mV threshold, the input latch is

reset and the gate is quickly discharged via a large

N-channel transistor.

Controlled Gate Rise and Fall Times

When the input is switched ON and OFF, the gate is

charged by the internal charge pump and discharged in a

controlled manner. The charge and discharge rates have

GATE

STATUS

SWITCH OFF

SWITCH ON

SWITCH LATCHED OFF

(OVER CURRENT)

SWITCH LATCHED OFF

(SHUTDOWN)

INPUTS

OUTPUTS

SWITCH

CONDITION

L = LOGIC LOW

H = LOGIC HIGH

X = IRRELEVANT

= EDGE TRIGGERED

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