Detailed description and application hints LNBP8L - LNBP9L - LNBP10L - LNBP11L
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protection. When an overload occurs the device limits the output current for the
time T
ON
depending on the C
EXT
value (see Figure 24 and Figure 25). When T
ON
has elapsed, the output goes low for a time of T
OFF
= 12 x T
ON
. This keeps the
power dissipated by the device low in overload conditions, and avoids the need for
an oversized heat sink in this condition. For the IPPAK package, when the
overload or the short-circuit occurs, the device clamps the output current in a
range between 550 mA and 850 mA.
7. EXTM modulates the V
OUT
by means of a capacitor connected in series (see Figure 6).
The following equation is used to calculate the peak-to-peak voltage of V
OUT
:
V
OUT
(AC) = V
EXTM
(AC) x G
EXTM
where V
OUT
(AC) and V
EXTM
(AC) are, respectively, the peak-to-peak voltage of V
OUT
and
V
EXTM
. G
EXTM
is the external modulation gain.
6.1 Input voltage protection
In some cases two or more receivers share the same coaxial cable, rendering their outputs
hard-paralleled, so the same voltage is present at the outputs of the receivers. If a receiver
is not disconnected at the mains, a current will flow from the OUTPUT to the V
CC1
or V
CC2
pins, depending the EN/VSEL pin setting. To avoid this, two diodes (only one for the IPPAK
package) in series are recommended at input pins V
CC1
and V
CC2
(see Figure 3). These
diodes do not cause a change at V
OUT
, but only a voltage drop, which can be minimized by
using Schottky diodes. Diodes used in Figure 4 and Figure 5 must withstand a continuous
current of almost 1 A and a breakdown voltage of 30 V (suggested type is 1N4001 or
BYV10-30). Be aware that the minimum voltage needed at the V
CC
pins must be respected,
considering the voltage drop across the input diodes).
Figure 6. EXTM application circuit
VCC
EN/VSEL (Tristate)
OUTPUT
GND
EXTM
D1
1N4001
Vextm
23V
LNBP8/9L
C2
220nF
C1
10µF
LNB OUTPUT
C3
100nF
D2
1N5818
C4
1µF
