LTM2881 datasheet(14/20 Pages) LINER

14 / 20 page

LTM2881

2881f

Figure 10. Equivalent Input Resistance into A and B

60Ω

2881 F10

>96k

APPLICATIONS INFORMATION

Receiver Input Resistance

The receiver input resistance from A or B to GND2 is greater

than 96k permitting up to a total of 256 receivers per system

without exceeding the RS485 receiver loading speciﬁcation.

The input resistance of the receiver is unaffected by

enabling/disabling the receiver or by powering/unpowering

the part. The equivalent input resistance looking into A and

B is shown in Figure 10.

Figure 13. Termination Magnitude and Phase vs Frequency

Figure 12. Termination Resistance vs Common Mode Voltage

Figure 11. Curve Trace Between A and B with Termination

Enabled and Disabled

Switchable Termination

Proper cable termination is very important for

signal ﬁdelity. If the cable is not terminated with its

characteristic impedance, reﬂections will distort the

signal waveforms.

The integrated switchable termination resistor provides

logic control of the line termination for optimal perfor-

mance 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 11 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 12. The integrated termination resistor has a high

frequency response which does not limit performance at

the maximum speciﬁed data rate. Figure 13 shows the

magnitude and phase of the termination impedance versus

frequency. The termination resistor cannot be enabled by

TE if the device is unpowered, ON is low or the LTM2881

is in thermal shutdown.

2881 F11

COMMON MODE VOLTAGE (V)

130

128

126

124

122

120

118

116

114

112

110

2881 G11

–5

–10

FREQUENCY (MHz)

150

140

130

120

110

100

–10

–20

–30

–40

2881 F13

0.1

PHASE

MAGNITUDE

LTM2881 Datasheet(PDF) 14 Page - Linear Technology

LTM2881 Datasheet(HTML) 14 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL