Cirrus Logic CDB470xx - Manual (Page 53)

CDB47xxS Single-Ended Schematic Descriptions
CDB47xxx User’s Manual
DS886DB11 Copyright 2014 Cirrus Logic, Inc 6-2
The audio output connectors consist of the following:
• 1 RCA jack for coaxial S/PDIF output
• 1 optical jack for S/PDIF output
• 1 2x10 header for serial audio data (I
2
S)
There is one control connector - JP1. This 20-pin connector provides pins for the following functions:
• Serial control interface for configuring the DSP
• Reset line for the DSP
• Proprietary serial debug interface
Jumper (J28) can be used to bypass the on-board MCU and enable use of JP1. While this header is
configured for MCU control (pins 2-3), the MCU will continue to drive all control lines to the CS470xx.
6.2.4 Memory
Figure 6-5 shows the schematic for the SPI Flash and I
2
C EEPROM devices. The CDB47xxxS is
designed with 32Mbits of SPI Flash and 512 kbit on-board. The serial control port for each device is
routed to the daughtercard connector J2.
6.2.5 Microphone Preamplifier
Figure 6-6 shows the microphone preamplifier for the CDB47xxxS, which has a 1/8” microphone input
jack to allow direct connection to an encapsulated condenser microphone (ECM). Because the output of
the ECM is so small, a pre-amplifier is needed to boost the signal to a line-level voltage.
These specifications for the amplifier are noted on the schematic page. These parameters should be
considered when choosing the microphone to be connected to the CDB47xxxS. Too large of a signal on
the ADC input will result in distortion of the sampled signal.
It is important to note that although the amplifier circuit shown is non-inverting (the input to U19-B is the
same polarity as the output from U19-C), the output of an ECM is inherently inverted since it acts as an
open-collector device. Therefore the microphone signal driven to the CS470xx should be considered an
inverted signal for processing purposes.
6.2.6 Power
Figure 6-7 shows the schematics for power on the CDB47xxxS board.
The DC input connector (J22) for the CDB47xxxS can accept +9 to +12 V DC , and the power supply should
be capable of supplying at least 2 amps of current.
The 4 voltage regulators on the CDB47xxxS generate the +1.8V, +3.3V, +5V and -5V necessary for
powering all of the ICs on the board. Note that the +5V, +3.3V and +1.8V regulators run directly off the DC
input supply connected to the CDB47xxxS. Also notice that the +1.8 V regulator is dependent upon +3.3V
power to enable it (not necessarily the 3.3 V regulator).
The 3 power jumpers (P1-P3) are used to choose between the on-board regulators, and an external
source for +5V, +3.3V, and +1.8V. This is a feature intended only for special applications, so these
jumpers should be left populated for normal operation.
6.2.7 Input Filters
Figure 6-8 shows the input CDB47xxxS. Each input of the CS470xx has its own input filter that consists of
a current limiter, an AC-coupling capacitor (10
F), and an anti-aliasing capacitor (2200 pF) which is not