IC-HF Datasheet, PDF (22/36 Pages) IC-Haus GmbH – 6-CH. ENCODER LINK, RS-422 DRIVER/RECEIVER

iC-HF
preliminary
6-CH. ENCODER LINK, RS-422 DRIVER/RECEIVER
Rev C1, Page 22/36
RS-422 RECEIVER CONFIGURATION
In A/B/Z and BiSS/SSI mode, BiSS bus structure mode,
and BiSS bus loopback mode some channels are con-
figured as RS-422 receivers. Table 9 presents the
function modes together with the channels that are con-
figured as RS-422 receivers.
Function mode RS-422 receiving channels
A/B/Z and BiSS/ISS
channel 5 and 6
BiSS bus structure
channel 4, 5 and 6
BiSS bus loopback
channel 4, 5 and 6
+10V
+200mV
-200mV
Vid
Vid
Transition
Region
Maximum
Operating
Range
-10V
Figure 25: RS-422 input maximum and minimum op-
erating voltages
Table 9: RS-422 receiving channels
Some parameters are important in characterizing the
receiver: the input voltage (VQi and VNQi), the differen-
tial voltage (Vid), and the common mode voltage (Vic),
where:
Vid = VQi − VNQi
Vic
=
VQi+VNQi
2
Figure 24 shows these voltages.
RS422 Input
Qi
Xi
+
VQi
Vid
-
NQi
VNQi
Vic
GND
Figure 24: RS-422 input sensitivity
Possible voltage ranges of RS-422
To comply with the possible voltage ranges of RS-422
standard, the RS-422 receiver must fulfill the following
requirements:
• Over an entire common mode voltage ranging from
-7 V to 7 V the receiver should not require a differen-
tial input voltage of more than |200 mV| to correctly
assume the intended binary state.
• The receiver has to maintain correct operation for dif-
ferential input voltages ranging from 200 mV to 10 V
in magnitude.
• The maximum input voltage (VQi, VNQi) shall not
exceed 10 V in magnitude.
• The receiver must be able to operate with a maximum
differential of 12 V without being damaged.
Figure 25 illustrates the minimum and maximum oper-
ating voltages of the receiver.
It is not allowed in iC-HF to apply negative input sig-
nals or signals higher than supply voltage. Following
these requirements, table 10 shows the sensitivity, the
minimum and the maximum values at the receiver.
Parameter Minimum Maximum
Vi
0V
5.5 V
|Vid|
50 mV
5.5 V
Vic
800 mV 5.5 V
Table 10: RS-422 sensitivity and input voltages
To comply with the total voltage ranges of RS-422 ex-
ternal resistors can be placed in line of the input pins
each receiver. The resistor value is 16.9 kΩ with a tol-
erance of 1%. The relative tolerance of both resistors
(matching) requires a tolerance of 0.1%.
An elegant solution is an integrated resistor network
with a matching better 0.1% e.g. :
• Vishay ACAS 0606 for a point-to-point BiSS interface
(MA+/- input) with two resistors each 4 pin package.
• Vishay ACAS 0612 for a BiSS bus structure interface
(MA+/-, SLI+/- inputs) with four resistors each 8 pin
package.
It is recommended to locate such optional resistors
closely and symmetrically to the related RS-422 input
pins. If these resistors are used, the sensitivity, the min-
imum, and the maximum input voltages at the receiver
are shown in table 11.
Parameter Minimum Maximum
Vi
-10 V
10 V
|Vid|
200 mV
12 V
Vic
-7 V
7V
Table 11: RS-422 sensitivity and input voltages with ex-
ternal resistors
In addition to the external resistors, the bus termination
resistor of 120 Ω should be placed between both inputs
of the receiver. Figure 26 shows this configuration.