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4 memory, 5 microphone preamplifier, 6 power – Cirrus Logic CDB470xx User Manual

Page 53: 7 input filters

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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