LNBH24 datasheet(5/30 Pages) STMICROELECTRONICS

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LNBH24

Introduction

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Introduction

The LNBH24 includes two completely independent sections. Except for the VCC and I²C

inputs, each circuit can be separately controlled and have independent external

components. The specification that follow should be considered equally for both sections

(A/B).

2.1

Application information

This IC has a built-in DC-DC step-up converter which, from a single 8 V to 15 V source,

generates the voltages (VUP) that allow the linear post-regulator to work at a minimum

dissipated power of 0.375 W Typ. @ 500 mA load (the linear post-regulator drop voltage is

internally held at VUP-VOUT=0.75 V typ.). An under voltage lockout circuit will disable the

entire circuit when the supplied VCC drops below a fixed threshold (6.7 V typically).

Note:

In this document the VOUT is intended as the Voltage present at the linear post-regulator

output (VoRX pin).

2.2

DiSEqC™ data encoding and decoding

The new internal 22 kHz tone generator (patent pending) is factory trimmed in accordance

with the standards, and can be selected through I²C interface TTX bit (or TTX pin) and

activated by a dedicated pin (DSQIN) which allows immediate DiSEqC™ data encoding, or

through TEN I²C bit in case the 22 kHz presence is requested in continuous mode. In

standby condition (EN bit LOW). The TTX function must be disabled setting TTX to LOW.

2.3

DiSEqC™ 2.0 implementation

The built-in 22 kHz Tone detector completes the fully bi-directional DiSEqC™ 2.0 (see Note:)

interfacing. Its input pin (DETIN) must be AC coupled to the DiSEqC™ bus, and extracted

PWK data are available on the DSQOUT pin. To comply with the bi-directional DiSEqC™ 2.0

bus hardware requirements an output R-L filter is needed. The LNBH24 is provided with two

output pins for each section, one for the DC voltage output (VoRX) and one for the 22 kHz

tone transmission (VoTX). The VoTX must be activated only during the tone transmission

while the VoRX provides the 13/18 V output voltage. This allows the 22 kHz Tone to pass

without any losses due to the R-L filter impedance (see Figure 4). During the 22 kHz

transmission, in DiSEqC™ 2.0 applications, activated by DSQIN pin or by the TEN bit, the

VoTX pin must be preventively set ON by the TTX function. This can be controlled both

through the TTX pin and the I²C bit. As soon as the tone transmission is expired, the VoTX

must be disabled by setting the TTX to LOW to set the device in the 22 kHz receiving mode.

The 13/18 V power supply is always provided to the LNB from the VoRX pin through the R-L

filter.

2.4

DiSEqC™ 1.X implementation

When the LNBH24 is used in DiSEqC™ 1.x applications the R-L filter is always needed for

the proper operation of the 22 kHz tone generator (patent pending. See Figure 4). Also in

this case, the TTX function must be preventively enabled before to start the 22 kHz data

transmission and disabled as soon as the data transmission has been expired. The tone can

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