Cirrus Logic CDB42428 - Manual (Page 4)

CDB42428
4
1. SYSTEM OVERVIEW
The CDB42428 demonstration board is an excellent means for evaluating the CS42428/26/18/16 family of highly
integrated CODECs. Analog and digital audio signal interfaces are provided, as well as a DB-25 computer parallel
port interface for use with the supplied Windows® configuration software.
The CDB42428 schematic set has been partitioned into 14 pages as shown in Figures 3 through 16.
1.1 CS424xx
A complete description of each member of the CS42428/26/18/16 family is included in each respective product data
sheet.
1.2 CS8406
The CS8406 S/PDIF transmitter on the demonstration board (see Figure 5) allows the performance of the CS424xx
internal ADC’s to be measured digitally. Either the CS424xx DAC port or the ADC port can be multiplexed to the
CS8406. The CS8406 transmitter is configured to operate in slave mode only, and will receive the required clocks
from the CS424xx. The data format for the CS8406 is selectable and must match that of its source. The CS8406
must be configured using the supplied software.
1.3 CS8416
The CS8416 S/PDIF receiver on the demonstration board (see Figure 5) allows the performance of the CS42428
internal DAC’s to be evaluated through the use of a digital (S/PDIF) input source. The CS8416 receiver interfaces
with the DSP header and can be configured to master the CS424xx DAC and ADC as well as the CS8406. The data
format is selectable and must match that of the CS424xx. The CS8416 must be configured using the supplied soft-
ware.
1.4 CS5361
There are two CS5361 A/D converters on the CS424xx demonstration board (see Figures 6 and 7). These convert-
ers supply the CS424xx ADCIN signals, and must operate in left-justified, 24-bit mode only. Their serial data outputs
are used when supporting the CS424xx One Line Mode of operation.
RCA analog connectors supply the inputs to each CS5361 channel through a unity gain, AC-coupled, single-to-
differential circuit. Each CS5361 input circuit is biased to 1/2 VA, and a 1V
RMS
signal will drive the converter to full
scale. The CS5361 converters are set to operate in slave mode and will receive their clocks from the CS424xx. The
SCLK and LRCK signals can be provided from either the CS424xx DAC or ADC port, and must be selected using
the configuration software.
1.5 Crystal Oscillator
Oscillator Y1 (see Figure 4) provides the System Clock (OMCK) for the CS424xx. The crystal oscillator on the board
is mounted in pin sockets that allow it to be removed or replaced. The board is shipped with a 24.576 MHz crystal
oscillator stuffed at Y1. Please refer to the CS424xx data sheet for details on OMCK operation.
The buffer on the output of the oscillator provides for signal level shifting to the proper VLS supply. This buffer can
be removed if the oscillator is powered from the same VLS voltage source as the codec.
Oscillator Y2 provides the OMCK clock for the CS8416. Please refer to the CS8416 data sheet for details on auto-
matic clock switching operation.This oscillator is not populated.
1.6 Analog Input
RCA phono connectors supply the CS424xx analog inputs through unity gain, AC-coupled single-to-differential cir-
cuits (see Figure 8). Each input circuit is biased to match the 2.7V
DC
VQ, and a 1V
RMS
differential signal will drive
the CS424xx converter to full scale.
1.7 Analog Outputs
Each CS424xx analog output is routed through a differential to single-ended, unity-gain low pass filter, which is AC-
coupled to an RCA phono jack (see Figures 9 through 12). The analog output filter on the CDB42428 has been de-
signed to add flexibility when evaluating the CS424xx DAC outputs. The output filter was designed in a two stage
format, with the first stage being an optional instrumentation amplifier, and the second stage a 2-pole butterworth
low pass filter.