LNBH29 datasheet(7/31 Pages) STMICROELECTRONICS

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LNBH29

Application information

2.7

Surge protection and TVS diodes

The LNBH29 series 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 Figure 3, to protect the STB output circuits where the LNBH29 and

other devices are electrically connected to the antenna cable.

Figure 3. 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

VMON: output voltage diagnostic

When device output voltage is activated (VOUT pin), its value is internally monitored and, as

long as the output voltage level is below the guaranteed limits, the VMON I²C bit is set to “1”.

See Table 12 for more details.

2.9

PDO: overcurrent detection on output pull-down stage

When an overcurrent occurs on the pull-down output stage due to an external voltage

source greater than the LNBH29 nominal VOUT and for a time longer than ISINK_TIME-OUT

(10 ms typ.), the PDO I²C bit is set to “1”. This may happen due to an external voltage

source presence on the LNB output (VOUT pin).

For current threshold and de-glitch time details, see Table 9.

2.10

Power-on I²C interface reset and undervoltage lockout

The I²C interface built into the LNBH29 series is automatically reset at power-on. As long as

the VCC stays below the undervoltage lockout (UVLO) threshold (4.7 V typ.), the interface

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

therefore keeping the power blocks disabled. Once the VCC rises above 4.8 V typ. the I²C

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

microprocessor.

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