LNBH23 Application information
Doc ID 13356 Rev 8 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
When V
SEL
=0 or 1 and LLC=0, the output voltage pin (V
oRX
) is internally monitored and, as
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
Tabl e 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
current diagnostic phase. When the AUX bit is set to HIGH, the V
oRX
is set to 22 V (typ.) and
V
UP
is set to 22.75 V (V
UP
= V
oRX
+0.75 V typ.) independently of the VSEL/LLC bits status. If
the AUX function is used to force the V
oRX
to 22 V, it is recommended to set the AUX bit to
LOW as soon as the minimum current test phase is expired, so that the V
oRX
voltage will be
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.
