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

SP3243E_102_060611

DESCRIPTION

The SP3243E transceivers meet the EIA/TIA-

232andITU-TV.28/V.24communicationprotocols

and can be implemented in battery-powered,

portable, or hand-held applications such as

notebook or palmtop computers. The SP3243E

devices feature Exar's proprietary and patented

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

cuitrythatgenerates±5.5VRS-232voltagelevels

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

SP3243EU devices can operate at a data rate

of 1000kbps fully loaded.

The SP3243E is a 3-driver/5-receiver device,

ideal for portable or hand-held applications.

The SP3243E 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 V

disconnected.

The SP3243E series is an ideal choice for power

sensitive designs.The SP3243E devices feature

power supply drain to a 1µA supply current.

In many portable or hand-held applications, an

RS-232cablecanbedisconnectedoraconnected

peripheral can be turned off. Under these condi-

tions,theinternalchargepumpandthedriverswill

be shut down. Otherwise, the system automati-

cally comes online. This feature allows design

engineers to address power saving concerns

without major design changes.

THEORY OF OPERATION

The SP3243E series is made up of four basic

circuit blocks:

1. Drivers

2. Receivers

3. the Exar proprietary charge pump, and

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-232-F and all previous

RS-232 versions. Unused drivers inputs should

be connected to GND or V

The drivers have a minimum data rate of 250kbps

(EB) or 1000kbps (EU) fully loaded.

Figure 11 shows a loopback test circuit used to

test the RS-232 Drivers. Figure 12 shows the

test results where one driver was active at 1Mbps

and all three drivers loaded with an RS-232 re-

ceiver in parallel with a 250pF capacitor. Figure

13 shows the test results of the loopback circuit

with all drivers active at 250kbps with typical

RS-232loadsinparallelwith1000pFcapacitors.A

superior RS-232 data transmission rate of 1Mbps

makes the SP3243EU an ideal match for high

speed LAN and personal computer peripheral

applications.

Figure 10. Interface Circuitry Controlled by Micropro-

cessor Supervisory Circuit

SP3243E

28

24

2

1

27

3

26

5KΩ

5KΩ

5KΩ

5KΩ

5KΩ

GND

C1+

C1-

C2+

C2-

V+

V-

14

13

12

20

19

18

17

16

15

0.1 µF

0.1 µF

0.1 µF

+

C2

C5

C1

+

+

C3

C4

+

+

0.1 µF

0.1 µF

9

10

11

4

5

6

7

8

RS-232

OUTPUTS

RS-232

INPUTS

23

22

21

25

R

ONLINE

SHUTDOWN

STATUS

UART

or

Serial µC

µ P

Supervisor

IC

TxD

RTS

DTR

RxD

CTS

DSR

DCD

RI

VIN

RESET