LT1342CSW datasheet(6/8 Pages) LINER

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LT1342

PI FU CTIO S

V–: Negative Supply Output (RS232 Drivers). V –

≈

–(2VCC – 2.5V). This pin requires an external charge

storage capacitor C

≥ 0.1µF. To reduce supply ripple,

increase the size of the storage capacitor.

C1+, C1–, C2+, C2–: Commutating Capacitor Inputs. These

pins require two external capacitors C

≥ 0.2µF: one from

C1+ to C1–, and another from C2+ to C2–. The capacitor’s

effective series resistance should be less than 2

Ω. For

≥ 1µF, low ESR tantalum capacitors work well in this

application, although small value ceramic capacitors may

be used with a minimal reduction in charge pump compli-

ance. For operation with an external 12V supply, omit C1

and connect the 12V supply to pin C1+. Pin V + may also be

shorted to C1+ when a separate supply is used. The 12V

supply must be bypassed with a 0.1F capacitor.

DRIVER IN: RS232 Driver Input Pins. These inputs are

compatible with TTL or CMOS logic. Tie unused inputs to

VCC or VL.

DRIVER OUT: Driver Outputs at RS232 Voltage Levels.

Driver output swing meets RS232 levels for loads up to

3k. Slew rates are controlled for lightly loaded lines.

Output current capability is sufficient for load condi-

tions up to 2500pF. Outputs are in a high impedance

state when in shutdown mode, VCC = 0V, or when the

DRIVER DISABLE pin is active. Outputs are fully short-

circuit protected from V – + 30V to V + – 30V. Applying

higher voltages will not damage the device if the over-

drive is moderately current limited. Short circuits on

one output can load the power supply generator and

may disrupt the signal levels of the other outputs. The

driver outputs are protected against ESD to

±10V for

human body model discharges.

RX IN: Receiver Inputs. These pins accept RS232 level

signals (

±30V) into a protected 5k terminating resistor.

The receiver inputs are protected against ESD to

±10kV for

human body model discharges. Each receiver provides

0.4V of hysteresis for noise immunity. Open receiver

inputs assume a logic low state.

RX OUT: Receiver Outputs with 3.3V Logic Compatible

Voltage Levels. Outputs are in a high impedance state

when in shutdown mode to allow data line sharing.

Outputs are fully short-circuit protected to ground or VCC

or VL with the power on, off, or in shutdown mode.

Receiver output level is determined by VL supply voltage.

Use VL = 3.3V for interfacing with 3.3V logic, VL = 5V for

interfacing with 5V logic.

ESD PROTECTIO

The RS232 line inputs of the LT1342 have on-chip protec-

tion from ESD transients up to

±10kV. The protection

structures act to divert the static discharge safely to

system ground. In order for the ESD protection to function

effectively, the power supply and ground pins of the

LT1342 must be connected to ground through low imped-

ances. The power supply decoupling capacitors and charge

pump storage capacitors provide this low impedance in

normal application of the circuit. The only constraint is that

low ESR capacitors must be used for bypassing and

charge storage. ESD testing must be done with pins VCC,

V+, V – and GND shorted to ground or connected with low

ESR capacitors.

ESD Test Circuit

LT1342 • ESD TC

5V VCC

0.1

µF

0.2

µF

0.1

µF

RS232

LINE PINS

PROTECTED

±10kV

LT1342

DRIVER 1 OUT

RX1 IN

DRIVER 2 OUT

RX2 IN

RX3 IN

RX4 IN

DRIVER 3 OUT

RX5 IN

3V VL

0.2

µF

DRIVER 1 IN

RX1 OUT

DRIVER 2 IN

RX2 OUT

RX3 OUT

RX4 OUT

DRIVER 3 IN

RX5 OUT

V–

V+

0.1

µF

GND

DRIVER DISABLE

0.1

µF

ON/OFF

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