Cirrus Logic CDB48500-USB - Manual (Page 34)

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A.1.1.1.8 Codec 1 and Codec 2 Input Filters (See Figure 1-8 )
Each input of the CS42448 has its own input filter that consists of a voltage divider, an AC-coupling capacitor
(10
F), and a anti-aliasing capacitor (2700 pF). The voltage divider is provided to make the CDB48500 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 . The 12 RCA jacks for analog inputs are also shown on this page.
A.1.1.1.9 Output Filters & Headphone Output (See Figure 1-9 )
A headphone Amp is provided on the AOUT7 and AOUT8 of the second CODEC. The output of the headphone
amp is connected to an 1/8” headphone output. The headphone maps to DAO2_D1 on the DSP. Refer to
section
Section 4.2.5, “Headphone Output” on page 4-8 for more details on the headphone output.
A.1.1.1.10 Mic and Pre-Amp (See Figure 1-10 )
The CDB48500 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 CDB48500. Too large of a signal on the CS42448 analog
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 U12-B is the same
polarity as the output from U12-C), the output of an ECM is inherently inverted since it acts as an open-collector
device. Therefore the microphone signal driven to the CS42448 should be considered an inverted signal for
processing purposes.
A.1.1.1.11 Control Connector and Power (See Figure 1-11 )
There is one control connector on the board, J11. This 50-pin connector provides pins for the following
functions:
• Serial control interface for configuring the DSP, codecs, and S/PDIF RX
• Reset lines for the DSP and other board devices
• Pins to provide power to the CDB USB MASTER USB control board
• An interface for delivering audio data to and from the USB board (feature not yet available)
The DC input connector (J25) for the CDB48500 can accept 9 to 12 V DC , and the power supply should be
capable of supplying at least 1 amp of current.
The 3 voltage regulators on the CDB48500 generate the 1.8V, 3.3V, and 5V necessary for powering all of the
ICs on the board. Note that the 5 V and 3.3 V regulators run directly off the DC input supply connected to the
CDB48500, while the 1.8 V regulator is dependent upon 3.3 V system power (not necessarily the 3.3 V
regulator).
The 3 power jumpers (J17, J18, J19) are used to choose between the on-board regulators, and an external
source for 5 V, 3.3 V, and 1.8 V. This is a feature intended only for special applications, so these jumpers should
be left in the ‘REG’ position for normal operation.
The DC input power jumper (J3) is used to bring the main 9 to 12V DC supply voltage from the control connector
(J11) rather than the standard DC input connector (J25). This jumper is not populated on the board, and is
intended only for special applications. J3 should not be used in normal operation.