4

Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50) 668-707 • www.exar.com

SP320_00_092208

±10Ω.

2. Resistance to ground of 150Ω ±15Ω,

measured from short-circuited terminals.

All of the V.35 receivers can operate at data

rates as high as 5Mbps. The sensitivity of

the V.35 receiver inputs is ±300mV.

rs-232 (V.28) drivers

The RS-232 drivers are inverting transmit-

ters, which accept either TTL or CMOS

inputs and output the RS-232 signals with

an inverted sense relative to the input logic

levels. Typically, the RS-232 output voltage

swing is ±9V with no load, and ±5V minimum

with full load. The transmitter outputs are

protected against infinite short-circuits to

ground without degradation in reliability.

In the power off state, the output imped-

ance of the RS-232 drivers will be greater

than 300Ω over a ±2V range. Should the

input of a driver be left open, an internal

400kΩ pullup resistor to V

input high, thus committing the output to

a low state. The slew rate of the trans-

mitter output is internally limited to a

maximum of 30V/µs in order to meet the EIA

standards. The RS-232 drivers are rated for

20kbps data rates.

rs-232 (V.28) receivers

The RS-232 receivers convert RS-232

input signals to inverted TTL signals. Each

of the four receivers features 500mV of

hysteresis margin to minimize the effects

of noisy transmission lines. The inputs also

have a 5kΩ resistor to ground; in an open

circuit situation the input of the receiver

will be forced low, committing the output

to a logic high state. The input resistance

will maintain 3kΩ-7kΩ over a ±15V range.

Themaximumoperatingvoltagerangeforthe

receiver is ±30V, under these conditions the

input current to the receiver must be limited

to less than 00mA. The RS-232 receivers

can operate to beyond 20kbps.

cHArGe pUMp

ThechargepumpisanExarpatenteddesign

(U.S.5,306,954)andusesauniqueapproach

compared to older less-efficient designs.

The charge pump still requires four external

tHeorY oF operAtion

The

sp320 is a single chip +5V-only serial

transceiver that supports all the signals

necessary to implement a full V.35 interface.

Three V.35 drivers and three V.35 receivers

make up the clock and data signals. Four

RS-232(V.28)driversandfourRS-232(V.28)

receivers are used for control line signals for

the interface.

V.35 drivers

The V.35 drivers are +5V-only, low power

voltage output transmitters. The drivers do

not require any external resistor networks,

and will meet the following requirements:

1. Source impedance in the range of 50Ω

to 150Ω.

2. Resistance between short-circuited ter-

minals and ground is 150Ω ±15Ω.

3. When terminated with a 100Ω resistive

load the terminal to terminal voltage will be

0.55 Volts ±20% so that the A terminal is

positive to the B terminal when binary 0 is

transmitted, and the conditions are reversed

to transmit binary .

4. The arithmetic mean of the voltage of the

A terminal with respect to ground, and the B

terminal with respect to ground will not

exceed 0.6 Volts when terminated as in 3

above.

The V.35 drivers can operate at data rates

as high as 5Mbps. The driver outputs are

protected against short-circuits between

the A and B outputs and short circuits to

ground.

Two of the V.35 drivers, DRIN2 and DRIN3

areequippedwithenablecontrollines.When

theenablepinsarehighthedriveroutputsare

disabled,theoutputimpedanceofadisabled

driver will nominally be 300Ω. When the en-

able pins are low, the drivers are active.

V.35 receivers

The V.35 receivers are +5V only, low power

differential receivers which meet the follow-

ing requirements:

1. Input impedance in the range of 100Ω