7

LTC1348

DRIVER OUTPUT

RECEIVER OUTPUT

DRIVER INPUT

LTC1348 G06

DRIVER OUTPUT

RECEIVER OUTPUT

DRIVER INPUT

LTC1348 G07

LT1348 • F05

0.1

µF

0.1

µF

0.1

µF

0.1

µF

LTC1348

1

2

3

4

5

6

7

8

9

10

11

12

13

14

RX1 IN

RX2 IN

RX3 IN

RX4 IN

RX5 IN

28

27

26

25

24

23

22

21

20

19

18

17

16

15

DR1 IN

RX1 OUT

DR2 IN

RX2 OUT

RX3 OUT

RX4 OUT

DR3 IN

RX5 OUT

DREN

RXEN

GND

0.1

µF

0.1

µF

1000pF

0.1

µF

0.1

µF

0.1

µF

LTC1348

1

2

3

4

5

6

7

8

9

10

11

12

13

14

DR1 OUT

DR2 OUT

RX3 IN

RX4 IN

DR3 OUT

28

27

26

25

24

23

22

21

20

19

18

17

16

15

DRIVER 1 IN

RX1 OUT

DRIVER 2 IN

RX2 OUT

RX3 OUT

RX4 OUT

DRIVER 3 IN

RX5 OUT

DREN

RXEN

GND

0.1

µF

DR1 OUT

DR2 OUT

RX5 IN

DR3 OUT

RX1 IN

1000pF

1000pF

RX2 IN

Figure 5. Data Rate Evaluation Circuit

Figure 6. Driver Test Result at 120kbps

Figure 7. Driver Test Results at 250kbps

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

High Data Rates

The LTC1348 maintains true RS232

±5V minimum driver

output even at high data rates. Figure 5 shows a test circuit

with 2m wires connecting the two test chips. Both chips

are run from 3.3V supplies. Figure 6 shows the typical line

waveforms with all three drivers, loaded with 1000pF and

3k

Ω,togglingsimultaneouslyat120kbaud.Figure7shows

the same circuit with a single 1000pF/3k

Ω loaded driver

driven at 250kbaud, and the other two drivers loaded but

not toggling. This closely approximates the actual behav-

ior of an RS232 serial port, with only one driver (TX) driven

at high speed and the other two drivers (RTS and DTR)

driven at a relatively low data rate or at DC. Under the same

conditions, the LTC1348 can go as fast as 350kbaud and

still meet EIA562 (

±3.7V) minimum driver output levels.