Cirrus Logic CRD44800-ST-FB User Manual
CRD44800-ST-FB
60 W Full-Bridge Reference Design for the CS44800
Features
Eight full-bridge channels, 60 W each
Programmable load compensation
Power Supply Rejection (PSR) feedback
allowing amplifier to operate from low cost
linear unregulated power supplies
Peak signal limiting
Thermal and over-current protection
> 85% amplifier efficiency
Works with GUI to configure the board or in a
standalone mode for easy operation.
Demonstrates recommended layout and
grounding arrangements
Description
The CRD44800-ST-FB PWM Amplifier demonstrates
the CS44800, Cirrus’ eight-channel pure digital PMW
controller. This reference design implements an eightchannel amplifier which delivers 60 W per full-bridge
channel into 8 Ω loads using a single +30 V supply (at
I
10% THD+N). A 155 W Switched Mode Power Supply
(SMPS) is used to power the CRD44800-ST-FB.
As shown below, the CS44800 IC takes four stereo digital audio inputs in I²S format and converts them to PWM
outputs. This 64-pin LQFP IC provides an integrated
sample rate converter for 32 kHz-192 kHz input sample
rate support, volume up/down, speaker load compensation, peak limiting to prevent amplifier clipping, power
supply ripple compensation, and AM frequency interference elimination.
This reference design uses the the ST Micro STA500, an
integrated power stage back end for digital amplifiers
(four STA500 parts configured as full-bridges are used
for this eight-channel design). Current limiting and thermal protection are provided by the STA500.
The inductor/capacitor 2
nd
order low pass filter (LPF) removes high frequency components from the output
signal effectively converting it from digital to analog.
ORDERING INFORMATION
CRD44800-ST-FB Reference Design
155W Switched Mode
Power Suppl y
Audio Dri ver Board
+30V/+5V
I2S Clocks & Data
2
C Host Contro l
I
PSR Circui try
+30V
CS4461 ADC
CS44800
(PWM Controller)
PWM Outputs
To channels 3/4
To channels 5/6
To channels 7/8
+30V
LPF
ST Micro
STA500A
LPF
Channels 1 and 2 ( of 8)
8Ω
8Ω
Cirrus Logic, Inc.
www.cirrus.com
Copyright © Cirrus Logic, Inc. 2004
(All Rights Reserved)
DEC ‘04
DS632ARD1
1
TABLE OF CONTENTS
1. SCHEMATIC DESCRIPTIONS ................................................................................................. 3
1.1 CRD44800-ST-FB PWM Amplifier ..................................................................................... 3
1.2 CRD44800-ST-FB Driver Board ........................................................................................ 3
1.3 Switched Mode Power Supply ........................................................................................... 3
2. OPERATION INFORMATION ................................................................................................... 4
2.1 Power Supply Ratings ........................................................................................................ 9
2.2 Power Supply Decoupling .................................................................................................. 9
2.3 Electromagnetic Interference (EMI) ................................................................................. 10
2.3.1 Suppression of EMI at the Source ...................................................................... 10
3. SCHEMATICS.......................................................................................................................... 12
4. LAYOUT................................................................................................................................... 19
5. BILL OF MATERIALS ............................................................................................................. 22
6. TYPICAL PERFORMANCE PLOTS........................................................................................ 24
7. REVISION HISTORY .............................................................................................................. 28
LIST OF FIGURES
Figure 1. Speaker Terminal Configuration ......................................................................................5
Figure 2. CS44800 Dialog Tab........................................................................................................ 7
Figure 3. Advanced Register Debug Tab - CS44800 ...................................................................... 8
Figure 4. Power and Connectors................................................................................................... 12
Figure 5. CS44800 ........................................................................................................................ 13
Figure 6. Left/Right Back Surround Channels............................................................................... 14
Figure 7. Left/Right Surround Channels ........................................................................................ 15
Figure 8. LFE/Center Channels..................................................................................................... 16
Figure 9. Left/Right Channels........................................................................................................17
Figure 10. PSR Feedback ............................................................................................................. 18
Figure 11. Silk Screen Top............................................................................................................ 19
Figure 12. Topside Layer .............................................................................................................. 20
Figure 13. Bottomside Layer ......................................................................................................... 21
Figure 14. Bill of Materials .............................................................................................................22
Figure 15. Bill of Materials .............................................................................................................23
Figure 16. Frequency Response...................................................................................................24
Figure 17. THD+N vs. Frequency at 1 W, 10 W, and 20 W .......................................................... 25
Figure 18. THD+N vs. Power at 1 kHz .......................................................................................... 26
Figure 19. FFT at -60 dBFS and 1 kHz ......................................................................................... 27
CRD44800-ST-FB
LIST OF TABLES
Table 1. Revision History .............................................................................................................. 28
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CRD44800-ST-FB
1. SCHEMATIC DESCRIPTIONS
1.1 CRD44800-ST-FB PWM Amplifier
The CS44800 shown in Figure 2 employs a built-in Sample Rate Converter (SRC) to support
all popular sampling frequencies between 32 kHz and 192 kHz. The CS44800 produces a
PWM frequency of either 384 kHz or 768 kHz (refer to CS44800 data sheet). In this design,
analog or digital audio signals are always output at a 384 kHz PWM rate.
The CS4461 ADC is used to monitor the signal and line frequency related ripple that is inevitable on the power supply rail when the amplifiers operate. The ripple voltage is digitized
and fed back to the CS44800. The CS44800 uses this information to substantially reduce
ripple related distortion and noise in the audio output signal.
Four ST Micro STA500s provide the power back end to drive the speaker loads. Each
STA500 consists of a pair of fully current and temperature protected full-bridge PWM output
stages. The STA500 is optimized for use in open loop Class-D amplifier systems.
1.2 CRD44800-ST-FB Driver Board
The CRD44800-ST-FB Driver board provides a convenient source of PCM I²S signals to drive
the CRD44800-ST-FB PWM Amplifier board. Eight analog inputs allow multi-channel analog
audio signals to be used for evaluation of the amplifier. In addition, either optical or coaxial
stereo S/PDIF signals can be used to evaluate the amplifier. In this case, the left and right
digital input signals are distributed to each STA500.
The CRD44800-ST-FB Driver board provides two modes of operation: stand-alone and remote. In the stand-alone mode, basic evaluation of the CS44800 is possible. The user can
select between analog and digital S/PDIF input signals (jumpers J17 and J18), control the
system volume, mute and unmute the system (switch S2), and enable or disable switching
on the PWM output (switch S3).
In the Remote mode, the DB-9 connector (J14, labelled RS-232) is connected to a host PC.
All aspects of the CS44800 may then be evaluated using the supplied software.
1.3 Switched Mode Power Supply
The SMPS used for the CRD44800-ST-FB is a 155 W OEM supply. The supply provides
+30 V for the STA500 PWM back ends, and +5 V to power all the signal level circuitry. The
SMPS is fully over-current and over-temperature protected.
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CRD44800-ST-FB
2. OPERATION INFORMATION
Switches and Indicators (Located on the Driver Board):
RESET Pushbutton (S1) - forces a complete system reset.
MUTE Pushbutton (S2) - mutes the audio output of the CRD44800-ST-FB, but the PWM output
stage will continue switching.
RAMP UP/DN Pushbutton (S3) - enables/disables the PWM output stage from switching.
MUTE LED (D16) - indicates that the audio output is muted. The MUTE LED is also used during
CRD44800-ST-FB initialization (see below).
FAULT LED (D19) - indicates several types of fault conditions. If one (or more) of the PWM outputs is shorted, or the PWM back end overheats, the FAULT LED will light. Also, if either the
Optical or Coax digital input is selected as the system input and a valid digital signal is not
present, the FAULT LED will light. The FAULT LED is also used during CRD44800-ST-FB initialization (see below).
S/PDIF ERROR LED (D6) - indicates the absence of a valid S/PDIF signal into the CS8416.
Stand-alone Operation
The CRD44800-ST-FB evaluation system is prewired for stand-alone operation. The SMPS is a
universal input, 90-260VAC, 50/60Hz.
1) Attach the supplied power cord to the power entry module. Do not turn on the power yet.
2) Configure jumper J10 for the desired volume control mode. If J10 is in, the gain of the
CS44800 will be forced to 0dB, irrespective of the position of the volume control pot. If J10 is
out, the volume control pot determines the CS44800 gain.
3) Configure jumpers J17 and J18 for the desired mode of operation. The first three options are
stand-alone, while the final option is remote.
Function J17 J18
Analog Inputs 1 - 2 1 - 2
Coaxial S/PDIF 2 - 3 1 - 2
Optical S/PDIF 1 - 2 2 - 3
Remote Mode 2 - 3 2 - 3
4) If the Analog input mode is selected, configure jumpers J6 and J7 to select the sampling frequency for the CS5341s.
Sample Rate (Fs) J6 J7
48 kHz 2 - 3 2 - 3
96 kHz 1 - 2 2 - 3
192 kHz 2 - 3 1 - 2
5) Supply either analog signals (if the Analog input option is selected) or either coaxial or optical
digital PCM inputs (if the digital S/PDIF option is selected).
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CRD44800-ST-FB
6) Connect loudspeakers to the speaker output terminals. The Red terminal is speaker positive,
and the Black terminal is speaker negative. Note that in a full-bridge system like the
CDRD44800-ST-FB, neither speaker terminal is grounded. As a result, speaker switch boxes
with common negative terminals should not be used.
Rx Lx Rs Ls S C R L
Figure 1. Speaker Terminal Configuration
Turn the volume control fully counterclockwise and apply power using the power switch on the
power entry module. The Fault and Mute LEDs will both light briefly as the system is initialized.
Note that if either the Coax or the Optical input is selected, a valid digital signal must be provided
to the selected input so that the CRD44800-ST-FB can complete initialization. If a valid signal is
not present at the selected input, both the Fault and Mute LEDs will remain lit.
If one of the stand-alone modes is selected, the amplifiers should now be operating. Slowly advance the volume control clockwise until the desired volume is achieved. The MUTE pushbutton
(S2) may be used to mute and unmute the audio output. The RAMP UP/DN pushbutton (S3) will
enable or disable switching on the PWM back end.
Note that in the stand-alone mode, several system faults are indicated by the lighting of the red
Fault LED, D19. Typical causes for fault conditions are short circuited speaker outputs, thermal
shutoff of the power back end, or lack of a S/PDIF signal when either of the S/PDIF inputs is selected.
Remote Operation
The CRD44800-ST-FB may also be operated remotely via the Cirrus FlexGUI for complete control of all the features of the CS44800. Note that the Fault and Mute LEDs operate differently in
the remote mode. They indicate the selected audio signal input as explained below. Follow the
procedure below to set up remote operation.
1) Attach the supplied power cord to the power entry module. Do not turn on the power yet.
2) Configure jumpers J17 and J18 for remote operation. Jumpers J17 and J18 should have pins
2 and 3 connected for remote operation. Jumpers J6 and J7 should be removed completely.
3) Turn on the AC power. Press the Reset button on the driver board. Select the desired audio
input source by pressing the Mute button. The following table shows the inputs selections:
Selected Input Mute LED Fault LED
Analog Inputs On Off
Optical S/PDIF Off On
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CRD44800-ST-FB
Selected Input Mute LED Fault LED
Coaxial S/PDIF On On
4) Connect the DB-9 RS-232 port (J14) on the CRD44800-ST-FB Driver board to a PC serial
port.
5) Copy the CRD44800-ST-FB directory from the included CD-ROM to the users local hard
drive. Note that FlexGUI is only compatible with systems running Windows 98 or better (i.e.
Windows 98, ME, 2000, XP, etc.).
6) Modify the following line in the file “flexconfig.ini”, which is found in the FlexLoader application
directory. This line is found in the [CDB44800Comm] section of the ini file.
SERIAL = PI_Serial.dll, 2500, COM1, 38400
Replace “COM1” with the number of the serial communications (RS-232) port you are using
(COM1/COM2/COM3/COM4).
7) Start FlexGUI opening FlexLoader.exe. This application can be used to read and modify any
CS44800 register, and provides easy control over individual channel volumes.
The CS44800 Dialog tab provides high level control over the CS44800’s registers. Controls are
provided to change volume, mute, power down, ramp control, quantization level, SAI input format, minimum pulse width, and channel delay.
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CRD44800-ST-FB
Figure 2. CS44800 Dialog Tab
The Advanced Register Debug tab provides low level control over the CS44800 and CS8416 individual register settings. Each device is displayed on a separate tab. Register values can be
modified bitwise or bytewise. For bitwise, click the appropriate pushbutton for the desired bit. For
bytewise, the desired hex value can be typed directly in the register address box in the register
map.
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CRD44800-ST-FB
Figure 3. Advanced Register Debug Tab - CS44800
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CRD44800-ST-FB
System Issues
2.1 Power Supply Ratings
The required power supply current rating can be estimated as follows. 45 W is used as the
reference output power because this represents the typical full scale output with no clipping.
Assume the efficiency, η, is approximately 85% (this accounts for power to supply control
electronics and overhead), then for 45 W / 8 channels:
W
Total
P
Supply
P
Consequently the supply current is:
Supply
I
P
Total
P
V
Out
η
2
Supply
Supply
360
424
212
85.0
30
W
424
===
WP
===
212
W
2
W
V
A
1.7
===
The factor of 2 in the denominator of the P
calculation arises from the fact that for typical
Supply
consumer applications in A/V or DVD receivers, the power supply should be capable of providing ½ the total requirement for all channels operating at full power. This design guide is
still quite conservative, and gives more that adequate headroom in real applications.
2.2 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. While the PSR functionality of the CS44800 helps reduce power
supply noise feedthrough to the output, careful decoupling of the power stage supply rails is
essential. Referring to Figure 11, the top side of the CRD44800-ST-FB PWM amplifier board,
good decoupling practice is shown. Notice that the 0.1 µF ceramic capacitors are as close
as physically possible to the power pins of the STA500. 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. The real time PSR feedback of the CS44800/CS4461 can greatly
attenuate the induced voltages due to the power supply ripple current.
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