6

LT1237

PI FU CTIO S

quire two external capacitors C

tive series resistance should be less than 2

Ω. For C ≥ 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 compliance.

DRIVER IN: RS232 Driver Input Pins. These inputs are

TTL/CMOS compatible. Inputs should not be allowed to

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 conditions up to

2500pF. Outputs are in a high impedance state when in

pin is active. Outputs are fully short-circuit protected from

damage the device if the overdrive 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

±15kV for human body model discharges, ±8kV

for IEC 1000-4-2 contact mode discharges and

±15kV for

IEC 1000-4-2 air gap 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

±15kV for

human body model discharges,

±8kV for IEC 1000-4-2

contact mode discharges and

±15kV for IEC 1000-4-2 air

gap discharges. Each receiver provides 0.4V of hysteresis

for noise immunity. Open receiver inputs assume a logic

low state.

RX OUT: Receiver Outputs with TTL/CMOS Voltage Lev-

els. Outputs RX1, RX2, RX3, and RX4 are in a high

impedance state when in shutdown mode to allow data

line sharing. Outputs, including LOW-Q RX OUT, are fully

on, off, or in shutdown mode.

LOW Q-CURRENT RX IN: Low Power Receiver Input. This

special receiver remains active when the part is in shut-

down mode, consuming typically 60

µA. This receiver has

the same 5k input impedance and

±10kV ESD protection

characteristics as the other receivers.

LOW Q-CURRENT RX OUT: Low Power Receiver Output.

This pin produces the same TTL/CMOS output voltage

levels as receivers RX1, RX2, RX3, and RX4 with slightly

decreased speed and short-circuit current. Data rates to

120kbaud are supported by this receiver.

ESD PROTECTIO

The RS232 line inputs of the LT1237 have on-chip protec-

tion from ESD transients up to

±15kV for human body

discharges,

±8kV for IEC 1000-4-2 contact mode dis-

charges and

±15V for IEC 1000-4-2 air gap discharges.

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 LT1237 must be connected to ground through low

impedances. The power supply decoupling capacitors and

charge pump storage capacitors provide this low imped-

ance in normal application of the circuit. The only con-

straint is that low ESR capacitors must be used for

bypassing and charge storage. ESD testing must be done

connected with low ESR capacitors.

1237 TC01

1

µF

0.2

µF

0.1

µF

RS232

LINE PINS

PROTECTED

TO

±10kV

LT1237

1

2

3

4

5

6

7

8

9

10

11

12

13

14

DRIVER 1 OUT

RX1 IN

DRIVER 2 OUT

RX2 IN

RX3 IN

RX4 IN

DRIVER 3 OUT

RX5 IN (LOW-Q)

ON/OFF

28

27

26

25

24

23

22

21

20

19

18

17

16

15

0.2

µF

DRIVER 1 IN

RX1 OUT

DRIVER 2 IN

RX2 OUT

RX3 OUT

RX4 OUT

DRIVER 3 IN

RX5 OUT (LOW-Q)

0.1

µF

GND

DRIVER DISABLE

ESD Test Circuit