SP3220BET datasheet(9/18 Pages) SIPEX

9 / 18 page

Rev. 7/8/03

SP3220B/U +3.0 to +5.0V RS-232 Transceivers

DESCRIPTION

The SP3220B/U device meets the EIA/TIA-232

and V.28/V.24 communication protocols and

can be implemented in battery-powered,

portable, or hand-held applications such as

notebook or palmtop computers. The SP3220B/

U device features Sipex's proprietary on-board

charge pump circuitry that generates 2 x V

CC 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 +3.0V to +5.5V

systems, or +5.0V-only systems that require true

RS-232 performance. The SP3220B device has

a driver that can operate at a data rate of 250Kbps

fully loaded. The SP3220U can Operate at

1000Kbps

The SP3220B/U is a 1-driver/1-receiver device

ideal for portable or hand-held applications.

The SP3220B/U features a 1

µA shutdown mode

that reduces power consumption and extends

battery life in portable systems. Its receivers

remain active in shutdown mode, allowing

external devices such as modems to be

monitored using only 1

µA supply current.

THEORY OF OPERATION

The SP3220B/U device is made up of three basic

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

the Sipex proprietary charge pump.

Drivers

The drivers are inverting level transmitters that

convert TTL or CMOS logic levels to +5.0V

EIA/TIA-232 levels inverted 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 without degradation in reliability. Driver

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

with supply voltages as low as 2.7V.

The SP3220B drivers typically can operate at a

data rate of 250Kbps fully loaded with 3K

Ω in

parallel with 1000pF, ensuring compatibility

with PC-to-PC communication software.

The SP3220U drivers can guarantee a data rate

of 1000Kbps fully loaded with 3

Ω in parallel

with 250pF.

The slew rate of the SP3220B output is 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 meets the monotonicity

requirements of the standard.

Figure 12 shows a loopback circuit used to test

the RS-232 driver. Figure 13 shows the test

results of the loopback circuit with the SP3220B

driver active at 250Kbps with an RS-232 load in

parallel with a 1000pF capacitor. Figure 14

shows the test results where the SP3220U driver

was active at 1000Kbps and loaded with an RS-

232 receiver in parallel with a 250pF capacitor.

A solid RS-232 data transmission rate of 250Kbps

provides compatibility with many designs in

personal computer peripherals and LAN appli-

cations.

The SP3220B/U driver's output stage is turned

off (high-Z) when the device is in shutdown

mode. When the power is off, the SP3220B/U

device permits the outputs to be driven up to

+12V. The driver's input does not have pull-up

resistors. Designers should connect an unused

input to V

CC or GND.

In the shutdown mode, the supply current falls to

less than 1

µA, where SHDN = LOW. When the

SP3220B/U device is shut down, the device's

driver output is disabled (high-Z) and the charge

pump is turned off with V+ pulled down to V

and V- pulled to GND. The time required to exit

shutdown is typically 100

µs. Connect SHDN to

CC if the shutdown mode is not used. SHDN has

no effect on RxOUT. Note that the driver is

enabled only when the magnitude of V- exceeds

approximately 3V.

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