Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

SP2209E_100_071612

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THEORY OF OPERATION

The

SP2209E device is made up of four

basic circuit blocks:

1. Drivers

2. Receivers

3. The Exar proprietary charge pump

4. Standby circuitry

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. With V

DD

= +12V, the typical RS-232 output voltage

swing is +9V with no load and +5V minimum

fully loaded. Unused driver input may be left

unconnected with an internal pull-up resis-

tor pulling the inputs high forcing the driver

outputs into a low state. The driver outputs

are protected against infinite short-circuits

to ground without degradation in reliability.

These drivers comply with the EIA/TIA-232F

and all other previous versions.

The drivers typically operate at a minimum

data rate of 460kbps fully loaded with 3kΩ in

parallel with 1000pF, ensuring compatibility

with PC-to-PC communication software.

The

SP2209E device is ideal for the new

generation modem standards which require

data rates greater than 460kbps. Refer to

Figures 3 and 5 for driver propagation delay

test circuit and waveforms, respectively.

Receivers

The Receivers convert EIA/TIA-232 levels

to TTL or CMOS logic output levels. Should

an input be left unconnected, an internal

5kΩ pulldown resistor to ground will commit

the output of the receiver to a HIGH state.

Receiver inputs are protected against over-

voltages of up to +/-15V. Refer to Figures

4 and 6 for receiver propagation delay test

circuits and waveforms, respectively.

DESCRIPTION

The

SP2209E device is a rugged, high

ESD, complete dual RS-232 port inte-

grated onto a single integrated circuit. Six

drivers and ten receivers provide a dual

port solution fully meeting the EIA/TIA-232

and ITU-T V.28/V.24 communication pro-

tocols and can be implemented in appli-

cations such as personal desktop comput-

ers and workstations. Refer to Figure 2

for a typical operating circuit.

Features include high transmission rates,

low power consumption, space saving

package dimensions, and compatibility

with the EU directive on electromagnetic

compatibility. EM compatibility includes

protection against radiated and con-

ducted interference including high levels

of electrostatic discharge. This device

is ideal for operation in electrically harsh

environments or where RS-232 cables are

frequently being plugged and unplugged.

This device is also immune to high RF

field strengths without special shielding

precautions. Emissions are also con-

trolled to within very strict limits.

The

SP2209E device features the inverter

portion of Exar's proprietary and patented

(U.S. 5,306,954) on-board charge pump

circuitry that generates a -9V voltage level

from a single +12V power supply. The

SP2209E device can operate at data rates

up to 460kbps fully loaded.

Its low power CMOS operation makes the

SP2209E device an ideal choice for power

sensitive designs. The

SP2209E device

has two receivers, one for each RS-232

port, that remains active in the standby

mode to allow the monitoring of peripheral

devices while the rest of the system is in a

power-saving standby mode. This allows

the

SP2209E device to wake up the entire

system when any communication is initi-

ated in peripheral devices. The

SP2209E

device has a low standby current of

100mA.