LNBH26L

Application information (valid for each section A/B)

Doc ID 022876 Rev 1

7/28

2.6

Diagnostic and protection functions

The LNBH26L has 4 diagnostic internal functions provided via the I²C bus, by reading 4 bits

on the STATUS1 register (in read mode). All the diagnostic bits are, in normal operation (that

is, no failure detected), set to LOW. One diagnostic bit is dedicated to the overtemperature

(OTF), and two bits (one per section) are dedicated to overcurrent (OLF-A, OLF-B). One bit

is dedicated to the input voltage power not good function (PNG). Once the OTF bit (or OLF-

A, OLF-B or PNG) has been activated (set to “1”), it is latched to “1” until the relevant cause

is removed and a new register reading operation is done.

2.7

Surge protection and TVS diodes

Each LNBH26L device section is directly connected to the antenna cable in a set-top box.

Atmospheric phenomenon can cause high voltage discharges on the antenna cable causing

damage to the attached devices. Surge pulses occur due to direct or indirect lightning

strikes to an external (outdoor) circuit. This leads to currents or electromagnetic fields

causing high voltage or current transients. Transient voltage suppressor (TVS) devices are

usually placed, as shown in the following schematic, to protect each section of STB output

circuits where the LNBH26L and other devices are electrically connected to the antenna

cable.

Figure 4.

Surge protection circuit

For this purpose the use of LNBTVSxx surge protection diodes specifically designed by ST

is recommended. The selection of the LNBTVS diode should be made based on the

maximum peak power dissipation that the diode is capable of supporting (see the LNBTVS

datasheet for further details).

2.8

Power-on I²C interface reset and undervoltage lockout

The I²C interface built into the LNBH26L is automatically reset at power-on. As long as the

not respond to any I²C command and all DATA register bits are initialized to zeroes,

interface becomes operative and the DATA registers can be configured by the main

microprocessor.