LNBH24

Introduction

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The LNBH24 is also compliant with the USA LNB power supply standards. In order to allow

fast transition of the output voltage from 18 V to 13 V and vice-versa, the LNBH24 is

provided with the VCTRL TTL pin which keeps the output at 13 V when it is set LOW and at

18 V when it is set HIGH or floating. VSEL and, if required, LLC bits must be set HIGH

before using the VCTRL pin to switch the output voltage level. If VCTRL=1 or floating, then

VSEL=LLC=1. This means that VCTRL=0 must be used only for short period to avoid the

higher power dissipation. In standby condition (EN bit LOW) all the I²C bits and the TTX pin

must be set LOW (if the TTX pin is not used it can be left floating but the TTX bit must be set

LOW during the standby condition).

2.8

Diagnostic and protection functions

The LNBH24 has 5 diagnostic internal functions provided via I²C BUS by reading 5 bits on

the system register (SR bits in read mode). All the diagnostic bits are, in normal operation

(no failure detected), set to LOW. Two diagnostic bits are dedicated to the over-temperature

and over-load protection status (OTF and OLF), while the remaining 3 bits are dedicated to

the output voltage level (VMON), 22 kHz Tone (TMON) and to the Minimum Load Current

diagnostic function (IMON).

2.9

Output voltage diagnostic

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

"1". The output voltage diagnostic is valid only with LLC=0 and AUX=0. Any VMON

information with LLC=1 and/or AUX=1 must be disregarded by the MCU.

2.10

22 kHz tone diagnostic

The 22 kHz tone can be internally detected and monitored If the DETIN pin is connected to

the LNB output bus (see typical application circuits) through a decoupling capacitor. The

Tone diagnostic function is provided with the TMON I²C bit. If the 22 kHz Tone amplitude

and/or the Tone frequency is out of the guaranteed limits (see TMON limits in the electrical

characteristics in Table 13), the TMON I²C Bit is set to "1".

2.11

Minimum output current diagnostic

In order to detect the output load absence (no LNB connected on the bus or cable not

connected to the IRD) the LNBH24 is provided with a minimum output current flag by the

IMON I²C bit in read mode, which is set to "1" if the output current is lower than 12 mA

typically with ITEST=1, and 6 mA with ITEST=0. The minimum current diagnostic function

(IMON) is always active. In order for it to function even in a multi-IRD configuration (multi-

switch), where the supply current could be sunk only from the higher supply voltage

LNBH24 output voltage as the highest voltage on the bus (22 V typ.) during the minimum