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

SP3220E_EB_EU_101_060311

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The

SP3220E/EB/EU devices meet the

EIA/TIA-232 and ITU-T V.28/V.24 commu-

nication protocols and can be implemented

in battery-powered, portable, or hand-held

applications such as notebook or palmtop

computers. The

SP3220E/EB/EU devices

feature

Exar's proprietary on-board charge

pump circuitry that generates ±5.5V for RS-

232 voltage levels from a single +3.0V to

+5.5V power supply. This series is ideal for

+3.3V-only systems, mixed +3.3V to +5.5V

systems, or +5.0V-only systems that require

true RS-232 performance. The

SP3220EB

device has a driver that can operate at a data

rate of 250kbps fully loaded.The

SP3220EU

can operate at 1000kbps; the

SP3220E

device can operate at a typical data rate of

235kbps when fully loaded.

The

SP3220E/EB/EUisa1-driver/1-receiver

device ideal for portable or hand-held ap-

plications. The

SP3220E/EB/EU features a

1µA shutdown mode that reduces power

consumption and extends battery life in por-

table systems. Its receivers remain active in

shutdown mode, allowing external devices

such as modems to be monitored using only

1µA supply current.

THEORY OF OPERATION

The

SP3220E/EB/EU series is made up of

three basic circuit blocks:

1. Driver

2. Receiver

3. The Exar proprietary charge pump

Driver

Thedriverisaninvertingleveltransmitterthat

converts TTL or CMOS logic levels to +5.0V

EIA/TIA-232 levels with an inverted sense

relative to the input logic levels. Typically,

the RS-232 output voltage swing is +5.5V

with no load and at least +5V minimum fully

loaded. The driver outputs are protected

against infinite short-circuits to ground with-

out degradation in reliability. Driver outputs

will meet EIA/TIA-562 levels of +/-3.7V with

supply voltages as low as 2.7V.

The

SP3220EB driver can guarantee a data

rate of 250kbps fully loaded with 3kΩ in

parallel with 1000pF, ensuring compatability

withPC-to-PCcommunicationsoftware.The

SP3220EU driver can guarantee a data rate

of 1000kbps fully loaded with 3kΩ in parallel

with 250pF.

The slew rate of the

SP3220E and

SP3220EB outputs are internally limited to a

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

standards (EIA RS-232D 2.1.7, Paragraph

5). The transition of the loaded output from

HIGH to LOW also meet the monotonicity

requirements of the standard. The slew rate

of the

SP3220EU is not limited. This allows

it to transmit at much faster data rates.

Figure 12 shows a loopback test circuit

used to test the RS-232 Driver. Figure

13 shows the test results of the loopback

circuit with the

SP3220EB driver active at

250kbps with RS-232 load in parallel with

a 1000pF capacitor. Figure 14 shows the

test results where the

SP3220EU driver

was active at 1000kbps and loaded with an

RS-232 receiver in parallel with 250pF ca-

pacitors. A solid RS-232 data transmission

rate of 250kbps provides compatibility with

many designs in personal computer periph-

erals and LAN applications.

The

SP3220E/EB/EU driver's output stage

is turned off (tri-state) when the device

is in shutdown mode. When the power is

off, the

SP3220E/EB/EU device permits

the outputs to be driven up to +/-12V. The

driver's inputs do not have pull-up resistors.

Designers should connect unused inputs to

Vcc or GND.

In the shutdown mode, the supply current

falls to less than 1µA, where SHDN = LOW.

When the

SP3220E/EB/EU device is shut

down, the device's driver output is disabled

DESCRIPTION