LT1330 datasheet(7/10 Pages) LINER

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LT1330

1330fb

ESD PROTECTION

The RS232 line inputs of the LT1330 have on-chip protection

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 LT1330 must

be connected to ground through low impedances. 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, VL, V+,

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

ESR capacitors.

1330 TC01

5V VCC

1μF

0.2μF

0.1μF

RS232

LINE PINS

PROTECTED

TO ±10kV

LT1330

DRIVER 1 OUT

RX1 IN

DRIVER 2 OUT

RX2 IN

RX3 IN

RX4 IN

DRIVER 3 OUT

RX5 IN (LOW-Q)

ON/OFF

3V VL

0.2μF

DRIVER 1 IN

RX1 OUT

DRIVER 2 IN

RX2 OUT

RX3 OUT

RX4 OUT

DRIVER 3 IN

RX5 OUT (LOW-Q)

V–

V+

0.1μF

GND

DRIVER DISABLE

0.1μF

ESD Test Circuit

APPLICATIONS INFORMATION

Storage Capacitor Selection

The V+ and V – storage capacitors must be chosen care-

fully to insure low ripple and stable operation. The LT1330

charge pump operates in a power efﬁcient Burst Mode®

operation. When storage capacitor voltage drops below

a preset threshold, the oscillator is gated on until V+ and

V– are boosted up to levels exceeding a second threshold.

The oscillator then turns off, and current is supplied from

the V+ and V – storage capacitors.

The V– potential is monitored to control charge pump

operation. It is therefore important to insure lower V+ ripple

than V – ripple, or erratic operation of the charge pump will

result. Proper operation is insured in most applications

by choosing the V+ ﬁlter capacitor to be at least 5 times

the V– ﬁlter capacitor value. If V+ is more heavily loaded

than V–, a larger ratio may be needed.

The V – ﬁlter capacitor should be selected to obtain low

ripple when the drivers are loaded, forcing the charge

pump into continuous mode. A minimum value 0.1μF is

suggested.

Do not attempt to reduce V– ripple when the charge pump

is in discontinuous Burst Mode operation. The ripple in this

mode is determined by internal comparator thresholds.

Larger storage capacitor values increase the burst period,

and do not reduce ripple amplitude.

Power Saving Operational Modes

The LT1330 has both shutdown and driver disable operating

modes. These operating modes can optimize power

consumption based upon applications needs.

The On/Off shutdown control turns off all circuitry except

for Low-Q RX5. When RX5 detects a signal, this information

can be used to wake up the system for full operation.

If more than one line must be monitored, the driver

disable mode provides a power efﬁcient operating option.

The driver disable mode turns off the charge pump and

RS232 drivers, but keeps all ﬁve receivers active. Power

consumption in driver disable mode is 3mA from VCC.

Burst Mode is a registered trademark of Linear Technology Corporation.

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