LTC485CS8 Linear Technology, LTC485CS8 Datasheet - Page 10

• Manufacturer Part Number: LTC485CS8
• Description: IC TXRX INTRFC RS485 LOPWR 8SOIC
• Manufacturer: Linear Technology
• Type: Transceiverr

Specifications of LTC485CS8

• Number Of Drivers/receivers: 1/1
• Protocol: RS485
• Voltage - Supply: 4.75 V ~ 5.25 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS INFORMATION
LTC485
LTC485 Line Length vs Data Rate
The maximum line length allowable for the RS422/RS485
standard is 4000 feet.
Using the test circuit in Figure 14, Figures 15 and 16 show
that with ~20V
line, The LTC485 is able to reconstruct the data stream at
the end of 4000 feet of twisted pair wire.
10
VOLTAGE (A + B)/2
COMMON MODE
VOLTAGE A – B
DIFFERENTIAL
TTL
IN
Figure 15. System Common Mode Voltage at 19.2kHz
LTC485
Figure 16. System Differential Voltage at 19.2kHz
GENERATOR
A
B
Figure 14. Line Length Test Circuit
NOISE
RO
RO
DI
DI
P-P
common mode noise injected on the
4000 FT 26AWG
TWISTED PAIR
C
100Ω
D
LTC485
485 F15
485 F16
485 F14
TTL
OUT
Figures 17 and 18 show that the LTC485 is able to com-
fortably drive 4000 feet of wire at 110kHz.
When specifying line length vs maximum data rate the
curve in Figure 19 should be used.
VOLTAGE (A + B)/2
COMMON MODE
COMMON MODE
VOLTAGE (A – B)
Figure 17. System Common Mode Voltage at 110kHz
Figure 18. System Differential Voltage at 110kHz
Figure 19. Cable Length vs Maximum Data Rate
100
10k
1k
10
10k
RO
RO
DI
DI
MAXIMUM DATA RATE
100k
1M
2.5M
485 F19
10M
485 F17
485 F18
485fh