LNBH23

Application information

7/32

This means that VCTRL=0 must be used only for short time to avoid the higher power

dissipation. In stand-by 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 stand-by condition).

2.7

Diagnostic and protection functions

The LNBH23 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 protections 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).

2.8

Output voltage diagnostic - VMON

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. Any VMON information with LLC=1

must be disregarded by the MCU.

2.9

22 kHz tone diagnostic - TMON

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

LNB output bus (see typical application circuits Figure 4) 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 Table 13), the TMON I²C bit is set to "1".

2.10

Minimum output current diagnostic - IMON

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

connected to the IRD) the LNBH23 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 to make it work even in a multi-IRD configuration (multi-

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

connected to the multi-switch box, the LNBH23 is provided with the AUX I²C bit which can

be set HIGH, in write mode by the MCU, before to read the IMON I²C bit status, to force the

LNBH23 output voltage as the highest voltage on the bus (22 V typ.) during the minimum

controlled again as per the VSEL/LLC bits status. In order to avoid false triggering, the

IMON function must be used only with the 22 kHz tone transmission deactivated

(TEN=TTX=0 and DSQIN=LOW), otherwise the IMON bit could be erroneously set to 0 even

if the output current is below the minimum current thresholds (6 mA or 12 mA). Any TMON

information with 22 kHz tone enabled must be disregarded by the MCU.