LNBH24_0808 STMICROELECTRONICS [STMicroelectronics], LNBH24_0808 Datasheet - Page 7

• Manufacturer Part Number: LNBH24_0808
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

2.8
2.9
2.10
2.11
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
V
be noted that the VCTRL pin controls only the linear regulator V
V
(keeping V
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).
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).
Output voltage diagnostic
When VSEL=0 or 1 and LLC=0, the output voltage pin (V
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.
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
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
connected to the multi-switch box, the LNBH24 is provided with the AUX I
LNBH24 output voltage as the highest voltage on the bus (22 V typ.) during the minimum
current diagnostic phase, the AUX I
status. When the AUX bit is set to HIGH, the V
OUT
UP
voltage is controlled only through the VSEL and LLC I²C bits. That is, even if VCTRL=0
=18.5 V (or 19.5 V if LLC=1). With VCTRL=0 V
OUT
=13.4 V) you will have V
Table
13), the TMON I²C Bit is set to "1".
2
C bit can be set HIGH before reading the IMON I
UP
=19.25 V typ when VSEL=1 and 20.25 V with
OUT
is set to 22 V (typ.) and the V
OUT
=13.4 V (LLC= either 0 or 1). Should
oRX
) is internally monitored and, as
OUT
stage while the step-up
2
C bit. To force the
UP
is set to
2
C bit
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