LNBP8L datasheet(10/21 Pages) STMICROELECTRONICS

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Detailed description and application hints

LNBP8L - LNBP9L - LNBP10L - LNBP11L

10/21

protection. When an overload occurs the device limits the output current for the

time TON depending on the CEXT value (see Figure 24 and Figure 25). When TON

has elapsed, the output goes low for a time of TOFF = 12 x TON. 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.

EXTM modulates the VOUT by means of a capacitor connected in series (see Figure 6).

The following equation is used to calculate the peak-to-peak voltage of VOUT:

VOUT(AC) = VEXTM(AC) x GEXTM

where VOUT(AC) and VEXTM(AC) are, respectively, the peak-to-peak voltage of VOUT and

VEXTM. GEXTM 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 VCC1 or VCC2

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 VCC1 and VCC2 (see Figure 3). These

diodes do not cause a change at VOUT, 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 VCC pins must be respected,

considering the voltage drop across the input diodes).

Figure 6.

EXTM application circuit

VCC

EN/VSEL (Tristate)

OUTPUT

GND

EXTM

1N4001

Vextm

23V

LNBP8/9L

220nF

10µF

LNB OUTPUT

100nF

1N5818

1µF

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