LTC2859/LTC2861

13

285961fc

from a driver transition may exceed the hysteresis levels

on the logic and data inputs pins causing an unintended

state change. This can be avoided by maintaining normal

logic levels on the pins and by slewing inputs through

their thresholds by faster than 1V/µs when transitioning.

Good supply decoupling and proper line termination also

reduces glitches caused by driver transitions.

Cable Length vs Data Rate

For a given data rate, the maximum transmission distance

is bounded by the cable properties. A typical curve of cable

length vs data rate compliant with the RS485 standard is

shown in Figure 14. Three regions of this curve reflect

different performance limiting factors in data transmis-

sion. In the flat region of the curve, maximum distance is

determined by resistive losses in the cable. The downward

sloping region represents limits in distance and data

rate due to AC losses in the cable. The solid vertical line

represents the specified maximum data rate in the RS485

standard. The dashed lines at 250kbps and 20Mbps show

the maximum data rates of the LTC2859/LTC2861 in Low-

EMI and normal modes, respectively.

Figure 14. Cable Length vs Data Rate

(RS485 Standard Shown in Solid Lines)

applicaTions inFormaTion

285961 F14

DATA RATE (bps)

10k

1M

10M

100k

100M

100

1k

10

10k

LOW-EMI MODE

MAX DATA RATE

RS485 MAX

DATA RATE

NORMAL

MODE MAX

DATA RATE

Multi-Node Network with End Termination Using LTC2859

Typical applicaTions

TE = 5V

TE = 5V

TE = 0V

R

D

TE = 0V

R

D

2859/61 TA04

R

D

LTC2859

R

D

LTC2859

LTC2859

LTC2859