LTC1348
APPLICATIONS INFORMATION
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
V
+
0.1µF
0.1µF
–
1
C2
+
2
3
LTC1348
28
27 C3
+
26
V
–
0.1µF
0.1µF
C2 4
V
CC
C1
+
5
0.1µF
DR1 OUT
C1
–
6
7
8
9
10
11
RX1 IN
DR2 OUT
RX2 IN
RX3 IN
12
RX4 IN
DR3 OUT 13
1000pF
RX5 IN
14
C3
–
25
DR1 IN
24
RX1 OUT
23
DR2 IN
22
RX2 OUT
21
RX3 OUT
20
RX4 OUT
19
DR3 IN
18
RX5 OUT
17
DREN
16
RXEN
15
GND
V
0.1µF
0.1µF
+
1
C2
+
C2
–
2
3
LTC1348
28
27
26
C3
+
V
–
0.1µF
4
V
CC
+
5
C1
0.1µF
6
C1
–
7
DR1 OUT
RX1 IN 8
9
DR2 OUT
RX2 IN 10
1000pF
RX3 IN
RX4 IN
DR3 OUT
RX5 IN
1000pF
11
12
13
14
C3
–
25
DRIVER 1 IN
24
RX1 OUT
23
DRIVER 2 IN
22
RX2 OUT
21
RX3 OUT
20
RX4 OUT
19
DRIVER 3 IN
18
RX5 OUT
17
DREN
16
RXEN
15
GND
LT1348 • F05
Figure 5. Data Rate Evaluation Circuit
LTC1348 G07
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.
U
W
U
U
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.
DRIVER OUTPUT
RECEIVER OUTPUT
DRIVER INPUT
LTC1348 G06
Figure 6. Driver Test Result at 120kbps
0.1µF
DRIVER OUTPUT
RECEIVER OUTPUT
DRIVER INPUT
Figure 7. Driver Test Results at 250kbps
7
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