IC-DL_17 Datasheet, PDF (7/10 Pages) IC-Haus GmbH – 3-CHANNEL DIFFERENTIAL LINE DRIVER

iC-DL
3-CHANNEL DIFFERENTIAL LINE DRIVER
DESCRIPTION
Rev C1, Page 7/10
Line drivers for control engineering couple TTL- or
CMOS-compatible digital signals with 24 V systems via
cables. The maximum permissible signal frequency is
dependent on the capacitive load of the outputs (cable
length) or, more specifically, the power dissipation in
iC-DL resulting from this. To avoid possible short circuit-
ing the drivers are current-limited and shutdown with
excessive temperature.
ther reflection of back travelling signals is prevented by
an integrated impedance network, as shown in Figure 3.
When the output is open the maximum output voltage
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
40
36
VB = 40 V
32
28
24
20
16
12
VB = 24 V
8
4
0
0
100
200
300
- I(A) [mA]
VE = hi
400
500
During a pulse transmission the amplitude at the iC-DL
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 reflected
wave superimposes with the transmitted wave and gen-
erates a signal with the double wave amplitude at the
receiving device.
Figure 2: Load dependence of the output voltage
(High-side stage)
Figure 4: Pulse transmission and transit times
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.
LINE EFFECTS
In PLC systems data transmission using 24 V sig-
nals usually occurs without a matched line termination.
A mismatched line termination generates reflections
which travel back and forth if there is also no line adap-
tation on the driver side of the device. With rapid pulse
trains transmission is disrupted. In iC-DL, however, fur-
After a further delay, the reflected wave also increases
the driver output to the full voltage swing. iC-DL’s inte-
grated impedance adapter prevents any further reflec-
tion and the achieved voltage is maintained along and
at the termination of the line.
A mismatch between iC-DL 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 between
30 and 140 Ω permit proper operation.