SI2107-X-FM SILABS [Silicon Laboratories], SI2107-X-FM Datasheet - Page 32

• Manufacturer Part Number: SI2107-X-FM
• Description: SATELLITE RECEIVER FOR DVB-S/DSS WITH QUICKLOCK AND QUICKSCAN
• Manufacturer: SILABS [Silicon Laboratories]

6.8. On-Chip LNB DC-DC Step-Up
In addition to the LNB signaling controller present on all
device versions, Si2108 and Si2110 devices contain an
internal supply controller circuit. This internal dc-dc
controller can be enabled via register bit LNB_EN. The
internal circuit requires the connection of an external
circuit with a specified bill-of-materials, and this
combination generates the selected LNB voltage with
superimposed one-way or two-way LNB signaling
communications. Si2108/10 devices include short-
circuit protection, overcurrent protection, and a step-up
dc-dc controller to implement a low-cost LNB power
supply using minimal external components. The
required circuit for DiSEqC1.x operation is illustrated in
Figure 9 on page 14. A circuit for DiSEqC2.x operation
is shown in Figure 6 on page 12.
When the LNB supply circuit is populated, the Si2108/
10 detects a connection to ground on the ISEN pin via
R10 during reset and configures the LNB pins for dc-dc
converter control instead of providing the interfaces to
an external LNB supply regulator discussed in the
previous section. See Table 17.
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. To compensate for long cable lengths, a 1 V
boost can be applied to both levels by setting the COMP
bit.
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.
Controller (Si2108/10 Only)
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. 0.81
the
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.
6.9. On-Chip Blindscan Controller:
QuickScan is comprised of a two stage process: a
blindscan stage and confirmation stage. It is an
automated
maximum RF frequency and symbol rate limits are
entered in the following registers BS_FMIN, BS_FMAX,
SRMIN, and SRMAX. After blindscan is completed, the
host may further use the resulting candidate channel
information (channel center frequencies and baud
rates) to try to actually acquire such channels by locking
the receiver to them. Further information such as C/N,
BER, channel program IDs, and etc. can be obtained
once the receiver locks to a candidate channel. Through
this
channels can be rejected.
6.9.1. Programming Sequence
If QuickScan is conducted whereby the symbol rate
search range is above 12.5 MBaud (for example
SRMIN = 2 MBaud and SRMAX = 20 MBaud) Silicon
Laboratories recommends that blindscan is performed
twice to ensure the most favorable estimates of channel
frequencies and symbol rates.
The programming sequence is as follows:
1. Program the frequency range (BS_FMIN, BS_FMAX) and
symbol rate range (SRMIN, SRMAX) values over which to
perform blindscan.
QuickScan (Si2109/10 Only)
confirmation
process
Si2107/08/09/10
process,
whereby
any
the
falsely
minimum
identified
and
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