IC-HX_17 Datasheet, PDF (9/14 Pages) IC-Haus GmbH – 3-CHANNEL DIFFERENTIAL COLD LINE DRIVER

iC-HX
3-CHANNEL DIFFERENTIAL COLD LINE DRIVER
Rev D1, Page 9/14
ing edge when over the double signal run time the
internal resistor forms a voltage divider with the charac-
teristic line impedance and is proportional to the length
of the connected line and the switching frequency. If
the internal resistor is perfectly matched to the charac-
teristic line impedance, the voltage divider generates
half the supply voltage at the line input, only supplying
the full voltage when an echo occurs. iC-HX exploits
this behavior of the open line in order to reduce the
power dissipation in the driver. A switch is triggered
by applying the halved low-impedance supply voltage,
buffered with capacitors, to the line input and termi-
nated by applying the internal resistor shortly before the
echo occurs. Power dissipation occurs regardless of
the length of the connected line in the time between the
application of the resistor to the line and the beginning
of the echo. In order to control this process iC-HX must
recognize the length of the connected line. The line is
measured using an integrated procedure which evalu-
ates the line echo. This principle of power dissipation
reduction only functions when a single wave travels
along the line. The maximum transmission frequency
with a reduced power dissipation is directly proportional
to the line length. If the transmission frequency is too
high for the line length, iC-xSwitch is no longer used, re-
sulting in increased power dissipation in the driver. The
required halved supply voltage is generated internally
in the chip and must be buffered by capacitors. On a
rising edge current flows from the capacitor into the line
and back into the capacitor on a falling edge. With the
differential operation of two lines the currents flow from
one line to the other and back again.
dissipation P_D(HX) occurs at intervals t1 to t4 and t5 to
t8. Figure 7 describes operation with iC-xSwitch; power
dissipation P_D(HX) occurs between t3 and t4 and t7
and t8. The mean power dissipation is significant for
the warming of the device, which is proportional to the
duty cycle. This results in a reduced power dissipation
(at the same frequency), meaning there is less power
dissipation with a shorter line or through the use of
iC-xSwitch with a long line, for example.
V(E)
V(A)
V(B)
ENHi
ENLo
ENxS
PD(HX)
Time
t1 t2 t4
t5 t6 t8
Figure 6: Power dissipation P_D(HX)
iC-xSwitch
without
Figure 5 shows the three switches, the integrated re-
sistor to match the characteristic line impedance and
V(E)
the connected line. VB is the positive power supply and
VB/2 is the half of it. The control of the switches de-
V(A)
pends on the input signals of the device and the length
of the connected line. With all enable-signals at lo-level
the output A is high impedance (tristate).
V(B)
VB
ENHi
ENHi
HiSwitch
Line
ENLo
ENxS
ENLo
LoSwitch
ENxS
xSwitch
VB/2
Figure 5: Circuit diagram with switches and line
PD(HX)
Time
t1 t2 t3 t4
t5 t6 t7 t8
Figure 7: Power dissipation P_D(HX) with iC-xSwitch
Figures 6 and 7 show the input signal V(E), the switch
trigger signals derived from this and the voltage curve at
the beginning (A) and end (B) of the line at intervals t1 to
t8. Figure 6 shows operation without iC-Xswitch. Power
An example for the power dissipation is given in figure
8. When xSwitch is not used by setting NXS to high,
the iC-HX behaves like the iC-DL.