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Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50)668-7000 • www.exar.com SP202E,232E,233E, 30E, 32E_00_0608

DESCRiPTion

DETAiLED DESCRiPTion

The SP202E, SP232E, SP233E, SP30E and

SP32A devices are a family of line driver and

receiver pairs that meet the EIA/TIA-232 and

V.28 serial communication protocols. The ESD

tolerance has been improved on these devices

to over +/-5kV for Human Body Model. These

devices are pin-to-pin compatible with Exar's

232A, 233A, 30A and 32A as well as popular

industry standards. This family of parts offer a

board charge pump that operates from a single

The SP202E, 232E, 233E, 30E and 32E de-

vices have internal charge pump voltage con-

verters which allow them to operate from a sin-

gle +5V supply. The charge pumps will operate

with polarized or non-polarized capacitors rang-

ing from 0. to 0µF and will generate the +/-6V

needed to generate the RS-232 output levels.

The SP233E design offers internal charge pump

capacitors. The SP30E provides an ON/OFF

input that simultaneously disables the internal

charge pump circuit and puts all transmitter and

receiver outputs into a high impedance state.

The SP32E is identical to the SP30E but with

seperate tri-state and shutdown inputs

Theory of operation

The SP202E, SP232E, SP233E, SP30E and

SP32E devices are made up of three basic

circuit blocks: 1. Drivers, 2. Receivers, and 3.

charge pump. Each block is described below.

Drivers

The drivers are inverting level transmitters that

convert TTL or CMOS logic levels to EIA/TIA-

232 levels with an inverted sense relative to

the input logic levels. The typical driver output

voltage swing is +/-6V. Even under worst case

loading conditions of 3k ohms and 2500pF, the

driver output is guaranteed to be +/-5.0V mini-

mum, thus satisfying the RS-232 specification.

The driver outputs are protected against infinite

short-circuits to ground without degradation in

reliability.

The slew rate of the driver output is internally

dards (EIA-232F). Additionally, the driver out-

puts LOW to HIGH transition meets the mon-

tonic output requirements of the standard.

Receivers

The receivers convert EIA/TIA-232 signal lev-

els to inverted TTL or CMOS logic output lev-

els. Since the input is usually from a transmis-

sion line, where long cable length and system

interference can degrade the signal, the inputs

have a typical hysteresis margin of 500mV. This

ensures that the receiver is virtually immune to

noisy transmission lines. The input thresholds

are 0.8V minimum and 2.8V maximum, again

well within the +/-3V RS-232 requirements.

Should an input be left unconnected, an internal

5kohm pull-down resistor to ground will commit

the output of the receiver to a HIGH state.

In actual system applications, it is quite pos-

sible for signals to be applied to receiver inputs

before power is applied to the receiver circuitry.

This occurs, for example, when a PC user at-

tempts to print, only to realize that the printer

wasn't turned on. In this case an RS-232 signal

from the PC will appear on the receiver input

at the printer. When the printer power is turned

on, the receiver will operate normally. All of

these devices are fully protected.

Charge pump

The charge pump is an Exar patented design

and uses a unique approach compared to

older less efficiant designs. The charge pump

requires 4 external capacitors and uses a four

phase voltage shifting technique. The internal

power supply consists of a dual charge pump

that provides a driver output voltage swing of

+/-6V. The internal oscillator controls the four

phases of the voltage shifting. A description of

each phase follows:

Phase 1

Vss charge store and double: The positive ter-

minals of capacitors C and C2 are charged

from Vcc with their negative terminals initially

connected to ground. C+ is then connected

to ground and the stored charge from C- is

superimposed onto C2-. Since C2+ is still con-

nected to Vcc the voltage potential across C2

is now 2 x Vcc.

Phase 2

Vss transfer and invert: Phase two connects

the negative terminal of C2 to the Vss storage

capacitor and the positive terminal of C2 to

ground. This transfers the doubled and invert-

ed (V-) voltage onto C4. Meanwhile, capacitor