SI4844-B20 Datasheet, PDF (17/27 Pages) Silicon Laboratories – BROADCAST ANALOG TUNING DIGITAL DISPLAY AM/FM/SW RADIO RECEIVER

Si4844-B20
4.10. Stereo DAC
High-fidelity stereo digital-to-analog converters (DACs)
drive analog audio signals onto the LOUT and ROUT
pins. The audio output may be muted.
4.11. Soft Mute
The soft mute feature is available to attenuate the audio
outputs and minimize audible noise in very weak signal
conditions. An advanced algorithm is implemented to
get a better analog tuning experience. The soft mute
feature is triggered by the SNR metric. The SNR
threshold for activating soft mute is programmable, as
are soft mute attenuation levels and attack and decay
rates.
4.12. Reference Clock
The Si4844-B supports programmable RCLK input (to
XTALI pin) with the spec listed in Table 7. It can be
shared with the host MCU to save extra crystal.
An onboard crystal oscillator is available to generate the
32.768 kHz reference when an external crystal and
load capacitors are provided. Refer to "AN602:
Si4822/26/27/40/44 Antenna, Schematic, Layout, and
Design Guidelines" for more details.
4.13. Reset, Powerup, and Powerdown
Setting the RSTB pin low will disable analog and digital
circuitry, reset the registers to their default settings, and
disable the bus. Setting the RSTB pin high will bring the
device out of reset.
Figure 1 shows typical reset, startup, and shutdown
timings for the Si4844-B. RSTB must be held low
(asserted) during any power supply transitions and kept
asserted as specified in Figure 1 after the power
supplies are ramped up and stable. Failure to assert
RSTB as indicated here may cause the device to
malfunction and may result in permanent device
damage.
A powerdown mode is available to reduce power
consumption when the part is idle. Putting the device in
powerdown mode will disable analog and digital circuitry
while keeping the bus active.
4.14. Memorizing Status
The Si4844-B provides the feature to memorize status
from the last power down with a simple design on PCB,
including frequency of the FM/AM/SW station. Refer to
“AN602: Si4822/26/27/40/44 Antenna, Schematic,
Layout, and Design Guidelines” for details.
4.15. Programming with Commands
To ease development time and offer maximum
customization, the Si4844-B provides a simple yet
powerful software interface to program the receiver. The
device is programmed using commands, arguments,
properties, and responses.
To perform an action, the user writes a command byte
and associated arguments, causing the chip to execute
the given command. Commands control an action such
as powerup the device, shut down the device, or get the
current tuned frequency. Arguments are specific to a
given command and are used to modify the command.
Properties are a special command argument used to
modify the default chip operation and are generally
configured immediately after powerup. Examples of
properties are de-emphasis and soft mute attenuation
threshold.
Responses provide the user information and are
echoed after a command and associated arguments are
issued. All commands provide a 1-byte status update,
indicating interrupt and clear-to-send status information.
For a detailed description of the commands and
properties for the Si4844-B, see "AN610: Si48xx ATDD
Programming Guide."
Rev. 1.0
17