CRD4525
2 x 15 W CS4525 Digital Amplifier Reference Design
Features
Description
Output Filters Optimized for 8 Ω Loads
The CRD4525 demonstrates the CS4525 digital PWM
controller with integrated power stages. This reference
design implements a two-channel amplifier which delivers 15 W per full-bridge channel into 8 Ω loads using a
single +18 V supply. The CRD4525 is powered by an included 80 W switching mode power supply.
Delivers 15 W/Ch into 8 Ω at 10 % THD+N
Single-Ended 2 VRMS Stereo Analog Inputs
Optical and Coaxial S/PDIF Inputs
Standard RCA phono jacks are provided to easily interface analog input signals with the evaluation board.
Optical and coaxial inputs are provided to interface with
S/PDIF digital audio input signals.
Flexible I/O Headers Provided
–
–
–
–
PCM Input Signal Interface
Auxiliary Serial Port Signal Interface
Delay Port Signal Interface
PWM Logic Level Signal Interface
The PWM audio power outputs are routed through an
inductor/capacitor 2nd order low-pass filter (LPF) to remove high frequency components from the output
signal, effectively converting it from digital to analog.
Optional CRD4412 Daughter-Card for
Subwoofer Channel
– Implements a 2.1 Configuration
The Windows software provides a GUI to make configuration of the CRD4525 easy. The software
communicates through the PC’s USB port to configure
the control port registers so that all features of the
CS4525 can be evaluated.
Demonstrates Recommended Layout and
Grounding Arrangements
+18 V Switching Mode Power Supply Included
Windows® Compatible Software Interface
–
–
Easy and Intuitive Graphical Interface
Supports USB PC Connectivity
ORDERING INFORMATION
CRD4525
CS4525 Reference Design
Stereo Analog
Inputs
Output
Filter
8Ω
Speaker
Connector
Optical
Receiver
CS4525
CS8416
S/PIDF
Receiver
PCM
Input
Header
Output
Filter
8Ω
Aux Port Header
Coaxial Input
CRD4412 Interface Header
USB
I/O
Status LED’s
Micro-controller
Tactile Controls
Power
Jack
Included 18 V Power Supply
http://www.cirrus.com
Copyright © Cirrus Logic, Inc. 2006
(All Rights Reserved)
SEPTEMBER '06
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CRD4525
TABLE OF CONTENTS
1. SYSTEM OVERVIEW ............................................................................................................................. 3
1.1 Power ............................................................................................................................................... 3
1.2 CS4525 Digital TV Amplifier ............................................................................................................ 3
1.3 CS8416 Digital Audio Receiver ........................................................................................................ 3
1.4 System Clocking .............................................................................................................................. 3
1.5 External Data Headers ..................................................................................................................... 3
1.6 Analog Inputs ................................................................................................................................... 4
1.7 Speaker Outputs .............................................................................................................................. 4
1.8 PC Interface ..................................................................................................................................... 4
1.9 Tactile Controls ................................................................................................................................ 4
1.10 CRD4412 Interface ........................................................................................................................ 4
2. PC SOFTWARE CONTROL ................................................................................................................... 6
2.1 CS4525 Main Controls Tab .............................................................................................................. 6
2.2 CS4525 Aux & Filter Controls Tab ................................................................................................... 7
2.3 S/PDIF Input Controls Tab ............................................................................................................... 8
2.4 Register Maps Tab ........................................................................................................................... 9
2.5 Pre-Configured Script Files ............................................................................................................ 10
2.5.1 Analog In ............................................................................................................................... 10
2.5.2 Optical SPDIF In .................................................................................................................... 10
2.5.3 Coaxial SPDIF In ................................................................................................................... 10
3. GROUNDING AND POWER SUPPLY DECOUPLING ........................................................................ 11
3.1 Power Supply Decoupling .............................................................................................................. 11
3.2 Electromagnetic Interference (EMI) ............................................................................................... 11
3.2.1 Suppression of EMI at the Source ......................................................................................... 11
4. SYSTEM CONNECTIONS & JUMPERS .............................................................................................. 13
5. CRD SCHEMATICS .............................................................................................................................. 14
6. CRD LAYOUT ...................................................................................................................................... 18
7. REVISION HISTORY ............................................................................................................................ 23
LIST OF FIGURES
Figure 1.Speaker Terminal Configuration ................................................................................................... 4
Figure 2.CS4525 Main Controls Tab ........................................................................................................... 6
Figure 3.CS4525 Aux & Filter Controls Tab ................................................................................................ 7
Figure 4.S/PDIF Input Controls Tab ............................................................................................................ 8
Figure 5.Register Maps Tab ........................................................................................................................ 9
Figure 6.CS4525 - Schematic Page 1 ....................................................................................................... 14
Figure 7.Power Outputs - Schematic Page 2 ............................................................................................ 15
Figure 8.S/PDIF Digital Audio Input - Schematic Page 3 .......................................................................... 16
Figure 9.Serial Control / Power - Schematic Page 4 ................................................................................. 17
Figure 10.Silkscreen Top .......................................................................................................................... 18
Figure 11.Topside Copper Layer .............................................................................................................. 19
Figure 12.Inner Copper Layer 1 ................................................................................................................ 20
Figure 13.Inner Copper Layer 2 ................................................................................................................ 21
Figure 14.Bottomside Copper Layer ......................................................................................................... 22
LIST OF TABLES
Table 1. System Connections ................................................................................................................... 13
Table 2. On-Board Tactile Controls ........................................................................................................... 13
Table 3. System Headers .......................................................................................................................... 13
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1. SYSTEM OVERVIEW
The CRD4525 reference design is an excellent means for evaluating the CS4525 30 W digital TV amplifier with integrated ADC. Analog and digital audio input signal interfaces are provided, an on-board microcontroller and USB
PC interface is used for easily configuring the CS4525’s internal registers, and a USB cable is included for use with
the FlexGUI Windows configuration software.
The CRD4525 schematic set is shown in Figure 6 through Figure 9.
1.1
Power
A 80 W OEM switching-mode power supply is included to power the CRD4525. The power supply provides
+18 V to the CS4525 power stages, and an on-board buck-converter and regulator provide power to the
logic-level digital circuitry.
Power must be supplied from the included power supply to the CRD4525 via the power connector J3 (see
the System Connections table on page 13).
1.2
CS4525 Digital TV Amplifier
A complete description of the CS4525 is included in the CS4525 product data sheet.
The required configuration settings of the CS4525 are achieved via its control port registers, accessible
through the CS4525 tab of the Cirrus Logic FlexGUI software. A register-level configuration interface is provided on the Register Maps tab. See the “PC Software Control” section on page 6 for more information.
1.3
CS8416 Digital Audio Receiver
A complete description of the CS8416 receiver (Figure 8 on page 16) and a discussion of the digital audio
interface are included in the CS8416 data sheet.
The CS8416 converts the input S/PDIF data stream into PCM data and clocks for the CS4525. The CS8416
operates in master mode and can provide PCM data in Left-Justified, I²S, Right-Justified 16-bit, and RightJustified 24-bit interface formats.
The most common operations of the CS8416 may be controlled via the S/PDIF Input Controls tab in the GUI
software application. Advanced options are accessible through the CS8416 sub-tab on the Register Maps
tab of the Cirrus Logic FlexGUI software.
1.4
System Clocking
A 24.576 MHz parallel resonant crystal, Y1, is available to provide a clock source to the CS4525. The crystal
is mounted in pin sockets, allowing easy removal or replacement. Alternatively, an input SYS_CLK signal
can be provided on pin 3 of the serial audio input header (J2).
1.5
External Data Headers
The evaluation board has been designed to allow interfacing with external systems via the headers J2, J4,
and J11. Figure 6 shows the headers’ electrical connections.
The 12-pin, 3 column header, J2, provides access to the CS4525’s serial audio input and SYS_CLK input
signals. Place shunts across the SCLK, LRCK, and SDIN pins located in the columns labeled “S/PDIF” to
connect to the on-board S/PDIF digital interface receiver circuitry. To use an external digital audio source,
simply remove the shunts and connect a ribbon across the SCLK, LRCK, and SDIN pins located in the columns labeled “EXT SAI”. A single ground column for the ribbon cable’s ground connection is provided to
maintain signal integrity.
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The 8-pin, 2 column header, J11, provides access to the CS4525’s auxiliary serial audio port output signals,
as well as the SYS_CLK output signal. A single ground column is provided to maintain signal integrity.
The 20-pin, 2 column header, J4, is included to interface with a CRD4412 card. Various signals, power, and
ground are presented on this header. Notably, this header includes the DLY_SDOUT and DLY_SDIN signals which can be used to interface with an external delay device or DSP. See Figure 6 for complete connectivity information.
1.6
Analog Inputs
RCA connectors supply the CS4525 analog inputs through single-ended passive circuits with one pole of
input filtering. A resistive attenuation network is implemented to allow 2 VRMS input levels to be supplied to
the CRD4525. Refer to the CS4525 data sheet for the maximum input signal level at the analog input pins.
1.7
Speaker Outputs
The CS4525 power outputs are configured for stereo parallel full-bridge operation. The outputs are routed
through a 2nd order low-pass filter to remove high-frequency content from the output signals and then presented at the speaker wire crimp terminals (J5). The output filters are optimized for 8 Ω speaker loads. The
speaker terminal connections are shown below.
R
L
Figure 1. Speaker Terminal Configuration
1.8
PC Interface
A USB connection is provided to facilitate software control of the CS4525’s internal registers.
A graphical user interface is available for the CRD4525 to allow easy manipulation of the CS4525’s internal
registers. See the CS4525 datasheet for complete internal register descriptions.
To enable the CRD4525, simply connect the supplied USB cable from an available USB port on a PC to the
USB connector (J37) and launch the Cirrus Logic FlexGUI software.
Refer to “PC Software Control” on page 6 for a description of the Graphical User Interface (GUI).
1.9
Tactile Controls
A volume control knob (S1), reset button (S2), and mute button (S3) are included for stand-alone operation
of the CRD4525. These controls are currently unsupported by the firmware running on the CRD4525, and
the PC interface must be used in order to operate the board.
The CRD4525 firmware is field-upgradable through the Cirrus Logic FlexGUI application. When available,
a new version of the FlexGUI (downloadable at www.cirrus.com/msasoftware) will automatically upgrade
the firmware upon its first launch.
1.10
CRD4412 Interface
A keyed connector (J4) is included to interface with the CRD4412. The CRD4525 can be used with or without a CRD4412 attached.
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Without the CRD4412 attached, the CRD4525 configures itself for 2-channel stereo full-bridge operation.
When the CRD4412 is attached, the CS4525 enables its bass manager and routes the LFE channel to the
CRD4412 which amplifies the signal in mono parallel full-bridge mode. Together, the CRD4525 and
CRD4412 implement a 2.1 configuration.
The CRD4412 must be inserted and removed while power is not applied to the CRD4525.
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CRD4525
2. PC SOFTWARE CONTROL
The CRD4525 is designed for use with the Microsoft Windows based FlexGUI graphical user interface. This interface provides comprehensive control over the CS4525’s internal registers via a PC’s USB port.
The FlexGUI software may be downloaded and installed from www.cirrus.com/msasoftware.
Step-by-step instructions for using the FlexGUI are provided as follows:
1. Download and install the FlexGUI software from www.cirrus.com/msasoftware.
2. Connect the CRD4525 to a host PC using the supplied USB cable.
3. Connect load speakers to the speaker output terminals.
4. Connect an input source to the S/PDIF or analog input connectors.
5. Plug the input to the included +18 V power supply into an available power outlet.
6. Plug the output of the included +18 V power supply into the power input connector on the CRD4525.
7. Launch the FlexGUI software. The GUI will load and be displayed.
8. Un-check the “Power Down CS4525” check box to power-up the device. In this state, the CRD4525 will convert and amplify the content present on the optical S/PDIF input.
2.1
CS4525 Main Controls Tab
The CS4525 Main Controls tab provides a high-level intuitive interface to many of the basic configuration
options of the CS4525. Use this tab to access functions such as power-down, input source, and volume control.
Figure 2. CS4525 Main Controls Tab
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2.2
CS4525 Aux & Filter Controls Tab
The CS4525 Aux & Filter Controls tab provides a high-level intuitive interface to many of the advanced configuration options of the CS4525. Use this tab to configure the auxiliary port, the internal filters, and advanced PWM adjustments. Control over device and board resets is also provided.
Figure 3. CS4525 Aux & Filter Controls Tab
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2.3
S/PDIF Input Controls Tab
When the CRD4525 is configured to make use of the CS8416 S/PDIF receiver, the devices must be configured for proper operation. The S/PDIF Input Controls tab provides a high-level intuitive interface to the most
common configuration options of the CS8416.
Figure 4. S/PDIF Input Controls Tab
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2.4
Register Maps Tab
The Register Maps tab provides an easy register-level interface to the on-board devices. Register values
can be modified on a bit-wise or byte-wise basis. To modify a single bit, first select the register by clicking
its position in the register matrix, then click the appropriate push-button for the desired bit. To modify an
entire register, simply enter the register’s new value directly into the register matrix.
Within the Register Maps tab, the CS4525 tab is used to access the CS4525’s internal registers, and the
CS8416 tab is used to access the CS8416’s internal registers.
Figure 5. Register Maps Tab
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CRD4525
2.5
Pre-Configured Script Files
Pre-configured script files are provided with the CRD4525 to allow easy initial board bring-up. The board
configurations stored within these files are described in sections 2.5.1 - 2.5.3.
2.5.1
Analog In
Using the pre-configured script file named “Analog In.fgs”, an analog input signal applied to the analog
inputs of the CRD4525 will be used as the CS4525’s input source. The device will be powered up with no
internal processing active and the master volume control set to -20 dB.
2.5.2
Optical SPDIF In
Using the pre-configured script file named “Optical SPDIF In.fgs”, the optical S/PDIF input signal will be
received by the CS8416 S/PDIF receiver. The CS8416 PCM output signals will be used as the CS4525’s
input source. The device will be powered up with no internal processing active and the master volume
control set to -20 dB.
2.5.3
Coaxial SPDIF In
Using the pre-configured script file named “Coaxial SPDIF In.fgs”, the coaxial S/PDIF input signal will be
received by the CS8416 S/PDIF receiver. The CS8416 PCM output signals will be used as the CS4525’s
input source. The device will be powered up with no internal processing active and the master volume
control set to -20 dB.
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3. GROUNDING AND POWER SUPPLY DECOUPLING
The CS4525 requires careful attention to power supply and grounding arrangements to optimize performance and
heat dissipation and minimize radiated emissions. Figure 10 on page 18 shows the component placement. Figure
11 on page 19 shows the top layout. Figure 14 on page 22 shows the bottom layout. The decoupling capacitors are
located as close to the CS4525 as possible. Extensive use of ground plane fill in the evaluation board yields large
reductions in radiated noise.
3.1
Power Supply Decoupling
Proper power supply decoupling is one key to maximizing the performance of a Class-D amplifier. Because
the design uses an open loop output stage, noise on the power supply rail will be coupled to the output.
Careful decoupling of the power stage supply rails is essential. Figure 10 on page 18 demonstrates good
decoupling capacitor placement. Notice that the small value decoupling capacitors are placed as close as
physically possible to the power pins of the CS4525. The ground side of the capacitors is connected directly
to top side ground plane, which is also used by the power supply return pins. This keeps the high frequency
current loop small to minimize power supply variations and EMI. 470 µF electrolytic capacitors are also located in close proximity to the power supply pins to supply the current locally for each channel. These are
not required to be expensive low ESR capacitors. General purpose electrolytic capacitors that are specified
to handle the ripple current can be used.
3.2
Electromagnetic Interference (EMI)
The EMI challenges that face a maker of Class-D amplifiers are largely the same challenges that have been
faced by the switch mode power supply industry for many years. The numerous EMI consulting firms that
have arisen and the many books that have been written on the subject indicate the scope of potential problems and available solutions. They should be considered a resource - most makers of switch mode equipment would benefit from developing a working relationship with a qualified EMI lab and from bringing their
experience to bear on design issues, preferably early in the design process.
This reference design is a board level solution which is meant to control emissions by minimizing and suppressing them at the source in contrast to containing them in an enclosure.
The EMI requirements for an amplifier have added dimensions beyond those imposed on power supplies.
Audio amplifiers are usually located in close proximity to radio receivers, particularly AM receivers which are
notoriously sensitive to interference. Amplifiers also need to operate with speaker leads of unpredictable
length and construction which make it possible for any high frequency currents that appear on the outputs
to generate nuisance emissions. The criteria for judging successful EMI control is not as well defined for
amplifier design as it is for power supplies. While the techniques of measuring conducted and radiated emissions are similar for both types of products, power supplies have a number of clearly defined (and legally
imposed) thresholds that are useful mainly as guidelines when testing amplifiers.
3.2.1
Suppression of EMI at the Source
Several techniques are used in the circuit design and board layout to minimize high frequency fields in the
immediate vicinity of the high power components. Specific techniques include the following:
• As mentioned in Section 3.1, effective power supply decoupling of high frequency currents, and minimizing the loop area of the decoupling loop is one aspect of minimizing EMI.
• Each output of the CS4525 includes “snubbing” components. For example, OUT1 and OUT2 include
snubber components R24 (20 Ω) and C23 (330 pF). These components serve to damp ringing on the
switching outputs in the 30-50 MHz range. The snubbing components should be as close as practical
to the output pins to maximize their effectiveness.
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• A separate ground plane with a solid electrical connection to the chassis and which surrounds the
speaker output connector should be implemented. This allows the speaker outputs to be RF decoupled
to the chassis just before they exit the chassis from the speaker connector.
• Make use of source termination resistors on all digital signals whose traces are longer than about
25 mm.
It is extremely critical that the layout of the power amplifier section of the CRD4525 be copied as exactly
as possible to assure best RF/EMI performance.
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4. SYSTEM CONNECTIONS & JUMPERS
Connector
Name
Reference
Designator
Signal
Direction
Power In
Left In
Right In
S/PIDF Input
S/PIDF Input
Speaker
Connector
USB
C2
J3
J1
J10
J6
J7
Input
Power connector. +18V.
Input
Analog input to CS4525.
Input
Input
Coaxial digital input to CS8416
Optical digital input to CS8416
J5
Output
J8
J9
Input/Output
Input/Output
Connector Function
Analog output from CS4525.
USB connection to PC for software control.
Connection for programming the on-board microcontroller (U3).
Table 1. System Connections
Control Name
Reference
Designator
Master Volume
Board Reset
Mute
S1
S2
S3
Tactile Control Function
Tactile controls not currently supported. See “Tactile Controls” on page 4.
Table 2. On-Board Tactile Controls
Connector Name
Reference
Designator
DSP IN
J2
DSP OUT
CRD4412 I/F
J11
J4
Header Function
When shunts are placed across column 1 and 2, the CS4525 serial audio
input data is sourced by the CS8416.
To use external serial audio input data, connect the PCM source cable
across column 2 and 3.
Auxiliary serial audio data from the CS4525.
Connection to CRD4412 daughter card.
Table 3. System Headers
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5. CRD SCHEMATICS
CRD4525
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Figure 6. CS4525 - Schematic Page 1
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CRD4525
Figure 7. Power Outputs - Schematic Page 2
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Figure 8. S/PDIF Digital Audio Input - Schematic Page 3
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Figure 9. Serial Control / Power - Schematic Page 4
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6. CRD LAYOUT
4.5”
2.65”
CRD4525
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Figure 10. Silkscreen Top
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Figure 11. Topside Copper Layer
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Figure 12. Inner Copper Layer 1
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Figure 13. Inner Copper Layer 2
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Figure 14. Bottomside Copper Layer
CRD4525
7. REVISION HISTORY
Release
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Changes
Initial Release
Contacting Cirrus Logic Support
For all product questions and inquiries, contact a Cirrus Logic Sales Representative.
To find the one nearest to you, go to www.cirrus.com.
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Cirrus Logic, Inc. and its subsidiaries ("Cirrus") believe that the information contained in this document is accurate and reliable. However, the information is subject
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