Cirrus Logic CRD49530-USB - Manual (Page 36)

5-3 Copyright 2008 Cirrus Logic DS705RD3
Detailed Schematic Descriptions
CRD49530-USB User’s Manual
The CS8416 has 5 different S/PDIF inputs available to it. Its internal multiplexer is used to select the
active source.
A general-purpose output of the CS8416 is used to generate an independent reset signal for the CS42448
audio codec. Providing a separate reset line for each audio device allows the system to sequence the
order in which audio devices come out of reset.
The CRD USB Master USB board acts as the host controller in the CRD49530 platform, and is connected
to the CRD49530 via J11 on page 8 of the schematics. The CRD USB Master drives the serial host
control port and CS8416_RESET signals on this page.
5.2.5 Audio CODEC
Figure 5-5 shows the schematic for the CS42448, which is a multi-channel ADC/DAC that is capable of
simultaneously supporting up to 6 channels of analog input and 8 channels analog output.
The serial host control port (SCL/CCLK, SDA/CDOUT, AD1/CDIN, AD0/CS) shares clock and data lines
with the CS4953xx and CS8416. The CS42448_CS line is unique to this chip and driven only when in SPI
mode. The pull-ups required for the SCL and SDA pins are shared with the other devices on the
CRD49530 board.
The CS42448_RST signal is a dedicated reset signal driven by a general-purpose output of the CS8416.
The CS42448 is a slave to the MUXED_MCLK signal, which is the master audio clock for the entire
CRD49530 system.
The CS42448 masters the CS8416_SCLK and CS8416_LRCLK signals which are used to shift I
2
S data
out of the CS42448 and shift I
2
S data into the CS4953xx.
The CS42448 slaves to the DSP_SCLK and DSP_LRCLK signals which are used to shift I
2
S data out of
the CS4953xx and shift I
2
S data into the CS42448.
The analog inputs and outputs of the CS42448 are being used in single-ended mode. This is evident
when looking at the input and output filter circuitry on page 6 of the schematics.
AIN5 of the CS42448 has an internal analog multiplexer that can be used to select between single-ended
inputs on the AIN5+ and AIN5- pins. This feature is used to share AIN5 between the microphone input
and RCA jack J27.
The transistor connected to MUTEC (Q1) provides the current drive necessary to drive all of the mute
transistors (see page 6 of schematic) into saturation.
The CRD USB Master USB board acts as the host controller in the CRD49530 platform, and is connected
to the CRD49530 via J11 on page 8 of the schematics. The CRD USB Master drives the serial host
control port signals shown on this schematic page.
5.2.6 Input/Output Filters
Figure 5-6 shows the input and output filters for the CRD530_USB board. Each input of the CS42448 has
its own input filter that consists of a voltage divider, an AC-coupling capacitor (10
μ
F), and a anti-aliasing
capacitor (2700 pF). The voltage divider is provided to make the CRD49530-USB capable of accepting
analog signals of up to 2 V
RMS . The CS42448 analog inputs register full-scale for an input amplitude of 1
V RMS .