7
LTC1348
APPLICATIONS INFORMATION
WUU
U
DRIVER OUTPUT
RECEIVER OUTPUT
DRIVER INPUT
LTC1348 G06
DRIVER OUTPUT
RECEIVER OUTPUT
DRIVER INPUT
LTC1348 G07
LT1348 • F05
0.1µF
0.1µF
0.1µF
0.1µF
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
V
–
V
+
V
CC
GND
0.1µF
0.1µF
1000pF
0.1µF
0.1µF
0.1µF
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
V
–
V
+
V
CC
GND
0.1µF
DR1 OUT
DR2 OUT
RX5 IN
DR3 OUT
RX1 IN
1000pF
1000pF
RX2 IN
C2
+
C3
+
C3
–
C3
+
C3
–
C2
–
C1
+
C1
–
C2
+
C2
–
C1
+
C1
–
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
3kΩ, toggling simultaneously at 120kbaud. Figure 7 shows
the same circuit with a single 1000pF/3kΩ 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.
