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LTC1157

PI FU CTIO S

Input Pins: The LTC1157 input pins are active high and

activate the charge pump circuitry when switched ON. The

LTC1157 logic inputs are high impedance CMOS gates

with ESD protection diodes to ground and supply and

therefore should not be forced beyond the power supply

rails.

Gate Drive Pins: 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 k

Ω). 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 LTC1157 should never

be forced below ground as this may result in permanent

damage to the device. A 300

Ω resistor should be inserted

in series with the ground pin if negative supply voltage

transients are anticipated.

OPERATIO

The LTC1157 is a dual micropower MOSFET driver de-

signed specifically for operation at 3.3V and 5V and

includes the following functional blocks:

3.3V Logic Compatible Inputs

The LTC1157 inputs have been designed to accommodate

a wide range of 3.3V and 5V logic families. Approximately

50mV of hysteresis is provided to ensure clean switching.

An ultra low standby current voltage regulator provides

continuous bias for the logic-to-CMOS converter. The

logic-to-CMOS converter output enables the rest of the

circuitry. In this way the power consumption is kept to an

absolute minimum in the standby mode.

Gate Charge Pump

Gate drive for the power MOSFET is produced by an

internal charge pump circuit which generates a gate volt-

age substantially higher than the power supply voltage.

The charge pump capacitors are included on-chip and

therefore no external components are required to generate

the gate drive.

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

been set to minimize RFI and EMI emissions.

BLOCK DIAGRA

(One Channel)

LOW STANDBY

CURRENT

REGULATOR

HIGH

FREQUENCY

OSCILLATOR

CHARGE

PUMP

LOGIC-TO-CMOS

CONVERTER

VOLTAGE

REGULATOR

INPUT

GND

GATE

GATE

DISCHARGE

LOGIC

LTC1157 • BD