LTC2855IGN datasheet(11/16 Pages) LINER

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LTC2854/LTC2855

285455fa

Switchable Termination

Proper cable termination is very important for good

signal ﬁdelity. If the cable is not terminated with its char-

acteristic impedance, reﬂections will result in distorted

waveforms.

The LTC2854/LTC2855 are the ﬁrst 3.3V RS485/RS422

transceivers to offer integrated switchable termination

resistors on the receiver input pins. This provides the

advantage of being able to easily change, through logic

control, the line termination for optimal performance when

conﬁguring transceiver networks.

When the TE pin is high, the termination resistor is enabled

and the differential resistance from A to B is 120Ω. Figure

10 shows the I/V characteristics between pins A and B

with the termination resistor enabled and disabled. The

resistance is maintained over the entire RS485 common

mode range of –7V to +12V as shown in Figure 11.

The integrated termination resistor has a high frequency

response which does not limit performance at the maximum

speciﬁed data rate. Figure 12 shows the magnitude and

phase of the termination impedance vs frequency.

Figure 10. Curve Trace Between A and B

with Termination Enabled and Disabled

Figure 11. Typical Resistance of the

Enabled Terminator vs Voltage on B Pin

Figure 12. Termination Magnitude

and Phase vs Frequency

10–1

100

FREQUENCY (MHz)

101

110

125

140

155

170

185

–75

–60

–45

–30

–15

285455 F12

MAGNITUDE

PHASE

COMMON MODE VOLTAGE (V)

–10

130

140

150

285455 F11

120

110

100

–5

VAB = 2V

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