iC-HX
3-CHANNEL DIFFERENTIAL COLD LINE DRIVER
Rev A1, Page 7/11
DESCRIPTION
Line drivers for control engineering couple TTL- or vented by an integrated impedance network, as shown
CMOS-compatible digital signals with 24 V systems via in Figure 3.
cables. The maximum permissible signal frequency is
dependent on the capacitive load of the outputs (ca-
T
iC−HX Eingang
ble length) or, more specifically, the power dissipation
in iC-HX resulting from this. To avoid possible short
iC−HX Ausgang
circuiting the drivers are current-limited and shutdown
with excessive temperature.
SPS Eingang
(100 m Leitung)
When the output is open the maximum output voltage
vert. 8 V/div
hor. 2 µs/div
corresponds to supply voltage VB (with the exception
of any saturation voltages). Figure 2 gives the typical
DC output characteristic of a driver as a function of the
load. The differential output resistance is typically 75 Ω
over a wide voltage range.
Figure 3: Reflections caused by a mismatched line
termination
During a pulse transmission the amplitude at the iC-
output initially only increases to half the value of sup-
ply voltage VB as the internal driver resistance and
characteristic line impedance form a voltage divider.
A wave with this amplitude is coupled into the line and
experiences after a delay a total reflection at the high-
impedance end of the line. At this position, the re-
flected wave superimposes with the transmitted wave
and generates a signal with the double wave amplitude
at the receiving device.
40
VE = hi
36
VB = 40 V
32
28
24
20
16
T
iC−HX Eingang
12
VB = 24 V
iC−HX Ausgang
8
4
0
SPS Eingang
(100 m Leitung)
180 ns
760 ns
0
100
200
300
400
500
vert. 8V/div hor. 500 ns/div
−I(A) [mA]
Figure 4: Pulse transmission and transit times
Figure 2: Load dependence of the output voltage
(High-side stage)
After a further delay, the reflected wave also increases
the driver output to the full voltage swing. iC-HX’s inte-
grated impedance adapter prevents any further reflec-
tion and the achieved voltage is maintained along and
at the termination of the line.
Each open-circuited input is set to low by an internal
pull-down current source; an additional connection to
GND increases the device’s immunity to interference.
The inputs are TTL- and CMOS-compatible. Due to
their high input voltage range, the inputs can also be
set to high-level by applying VCC or VB.
A mismatch between iC-HX and the transmission line
influences the level of the signal wave first coupled into
the line, resulting in reflections at the beginning of the
line. The output signal may then have a number of
graduations. Voltage peaks beyond VB or below GND
are capped by integrated diodes. By this way, trans-
misssion lines with a characteristic impedance of be-
tween 30 and 140 Ω thus permit correct operation of
the device.
LINE EFFECTS
In PLC systems data transmission using 24 V sig-
nals usually occurs without a matched line termina-
tion. A mismatched line termination generates reflec-
tions which travel back and forth if there is also no line
adaptation on the driver side of the device. With rapid
pulse trains transmission is disrupted. In iC-HX, how-
ever, further reflection of back travelling signals is pre- iC-xSwitch
ICHAUS [ IC-HAUS GMBH ]
