SI2107 SILABS [Silicon Laboratories], SI2107 Datasheet - Page 29

• Manufacturer Part Number: SI2107
• Description: SATELLITE RECEIVER FOR DVB-S/DSS
• Manufacturer: SILABS [Silicon Laboratories]

The LNB supply controller is disabled by default. To use
the supply, it must be enabled by setting the LNB enable
bit, LNB_EN. If the LNB supply circuit is connected, the
TFS bit is ignored; the internal LNB supply controller
uses its internal oscillator to generate the 22 kHz tone.
The TFQ setting can still be used to modify the nominal
frequency as explained earlier.
Selection
corresponding PWM control signal for the boost
converter. Since Japan uses a different LNB supply
voltage than the rest of the world (R.O.W.), the device
can be configured to either generate 13 V/18 V
(R.O.W.) or 12 V/15 V (Japan) dc levels via register bit
LNBLVL. To compensate for long cable lengths, a 1 V
boost can be applied to both levels by setting the COMP
bit.
Pin
10
12
Table 17. LNB Pin Configuration
7
9
8
of
high
Connected
or
VSEN
LNB2
LNB1
ISEN
PWM
LNB Supply Circuit
low
voltage
Unconnected
outputs
TGEN
TDET
DRC
DCS
NC
Preliminary Rev. 0.7
the
The nominal level of both the low- and high-output
voltages can be further fine-tuned using the VLOW and
VHIGH registers. Register bit LNBV selects whether to
output high or low dc voltage to the LNB. During
operation, the voltage level of the line can be monitored
via the VMON register.
The maximum current draw of the LNB supply can be
set using the IMAX register. The overcurrent threshold
of the LNB supply may be set via the ILIM register. If the
output current exceeds this value, the external LNB
power supply is automatically disabled, and the
overcurrent detect bit, OCD, is asserted. The device
attempts to restore normal operation after 1 s by
supplying power to the line. During the recovery period,
overcurrent detection is disabled for the time specified
by the OLOT register.
Short circuit protection circuitry operates in conjunction
with overcurrent detection to rapidly identify short-circuit
conditions. If the output is shorted to ground, the
external LNB power supply is automatically disabled,
and the short-circuit detect bit, SCD, is asserted. The
device attempts to restore normal operation after one
second by supplying power to the line. During the
recovery period, short-circuit detection is disabled for
the time specified by the SLOT register.
The LNB supply circuit is protected from an overvoltage
condition by design. In the event that the LNB supply
circuit is accidentally connected to a voltage source
greater than the intended output voltage, it remains
operational. The LNB supply circuit resumes normal
operation when the connection to the external voltage
source has been removed.
Si2107/08/09/10
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