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SP3223BCP

High Speed Intelligent +3.0V to +5.5V RS-232 Transceivers

Signal Processing Technologies 

DESCRIPTION

The SP3223B and SP3243B transceivers meet

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

munication protocols and can be implemented

in battery-powered, portable, or hand-held ap-

plications such as notebook or palmtop comput-

ers. The SP3223B and SP3243B devices feature

Sipex's proprietary and patented (U.S.--

5,306,954) on-board charge pump circuitry that

generates ±5.5V RS-232 voltage levels from a

single +3.0V to +5.5V power supply. The

SP3223B and SP3243B devices can operate at a

data rate of 250kbps fully loaded.

The SP3223B is a 2-driver/2-receiver device,

and the SP3243B is a 3-driver/5-receiver device

ideal for portable or hand-held applications.

The SP3243B includes one complementary

always-active receiver that can monitor an

external device (such as a modem) in shutdown.

This aids in protecting the UART or serial

controller IC by preventing forward biasing

of the protection diodes where VCC may be

disconnected.

VCC

UART

or

Serial µC

+

C5 0.1µF

28 C1+

+

C1 0.1µF

24 C1-

+

C2 0.1µF

1 C2+

2 C2-

TxD

14 T1IN

RTS

13 T2IN

DTR

12 T3IN

26

VCC

V+ 27

+

C3 0.1µF

SP3243B V- 3

T1OUT 9

T2OUT 10

T3OUT 11

C4 0.1µF

+

RS-232

OUTPUTS

RxD

CTS

DSR

DCD

RI

VCC

20 R2OUT

19 R1OUT

R1IN 4

18 R2OUT

17 R3OUT

5KΩ

R2IN 5

5KΩ

R3IN 6

16 R4OUT

5KΩ

R4IN 7

15 R5OUT

22 SHUTDOWN

23 ONLINE

5KΩ

R5IN 8

5KΩ

21 STATUS

GND

25

RS-232

INPUTS

RESET

µP

Supervisor

VIN

IC

Figure 16. Interface Circuitry Controlled by Micropro-

cessor Supervisory Circuit

The SP3223B and SP3243B series is an ideal

choice for power sensitive designs. The SP3223B

and SP3243B devices feature AUTO ON-LINE®

circuitry which reduces the power supply drain

to a 1µA supply current. In many portable or

hand-held applications, an RS-232 cable can be

disconnected or a connected peripheral can be

turned off. Under these conditions, the internal

charge pump and the drivers will be shut down.

Otherwise, the system automatically comes

online. This feature allows design engineers to

address power saving concerns without major

design changes.

THEORY OF OPERATION

The SP3223B and SP3243B series is made up

of four basic circuit blocks:

1. Drivers,

2. Receivers,

3. the Sipex proprietary charge pump, and

4. AUTO ON-LINE® circuitry.

Drivers

The drivers are inverting level transmitters that

convert 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 +5.4V with no load and

+5V minimum fully loaded. 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

previous RS-232 versions. Unused driver inputs

should be connected to GND or VCC.

The drivers can guarantee a data rate of 250kbps

fully loaded with 3kΩ in parallel with 1000pF,

ensuring compatibility with PC-to-PC commu-

nication software.

The slew rate of the driver 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.

Rev. 6/30/03

SP3223B/3243B +3.0V to +5.5V RS-232 Transceivers

10

© Copyright 2003 Sipex Corporation

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