iC-HX
3-CHANNEL DIFFERENTIAL COLD LINE DRIVER
Rev A1, Page 8/11
Power dissipation in the driver occurs with each switch- at the beginning (A) and end (B) of the line at intervals
ing edge when over the double signal run time the in- t1 to t8. Figure 6 shows operation without iC-Xswitch.
ternal resistor forms a voltage divider with the charac- Power dissipation PD(HX) occurs at intervals t1 to t4
teristic line impedance and is proportional to the length and t5 to t8. Figure 7 describes operation with iC-
of the connected line and the switching frequency. If xSwitch; power dissipation PD(HX) occurs between t3
the internal resistor is perfectly matched to the charac- and t4 and t7 and t8. The mean power dissipation is
teristic line impedance, the voltage divider generates significant for the warming of the device, which is pro-
half the supply voltage at the line input, only supplying portional to the duty cycle. This results in a reduced
the full voltage when an echo occurs. iC-HX exploits power dissipation (at the same frequency), meaning
this behavior of the open line in order to reduce the there is less power dissipation with a shorter line or
power dissipation in the driver. A switch is triggered through the use of iC-xSwitch with a long line, for ex-
by applying the halved low-impedance supply voltage, ample.
buffered with capacitors, to the line input and termi-
nated by applying the internal resistor shortly before
the echo occurs. Power dissipation occurs regardless
V(E)
of the length of the connected line in the time between
the application of the resistor to the line and the begin-
ning of the echo. In order to control this process iC-HX
V(A)
must recognize the length of the connected line. The
line is measured using an integrated procedure which
evaluates the line echo. This principle of power dis-
V(B)
sipation reduction only functions when a single wave
ENHi
travels along the line. The maximum transmission fre-
ENLo
quency with a reduced power dissipation is directly
proportional to the line length. If the transmission fre-
quency is too high for the line length, iC-xSwitch is no
ENxS
longer used, resulting in increased power dissipation in
the driver. The required halved supply voltage is gen-
PD(HX)
erated internally in the chip and must be buffered by
Time
t1 t2
t4
t5 t6
t8
capacitors. On a rising edge current flows from the ca-
pacitor 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.
Figure 6: Power dissipation PD(HX) without iC-
xSwitch
V(E)
V(A)
Figure 5 shows the three switches, the integrated re-
sistor to match the characteristic line impedance and
the connected line. VB is the positive power supply
and VB/2 is the half of it. The control of the switches
depends 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)
ENHi
ENLo
ENxS
VB
ENHi
HiSwitch
Line
PD(HX)
Time
LoSwitch
ENxS
ENLo
xSwitch
t1 t2 t3 t4
t5 t6 t7 t8
VB/2
Figure 7: Power dissipation PD(HX) with iC-xSwitch
Figure 5: Circuit diagram with switches and line
An example for the power dissipation is given in figure
Figures 6 and 7 show the input signal V(E), the switch 8. When xSwitch is not used by setting NXS to high,
trigger signals derived from this and the voltage curve the iC-HX behaves like the iC-DL.
ICHAUS [ IC-HAUS GMBH ]
