w WM9082
PDM Input Mono 3W Class D Speaker Driver
WOLFSON MICROELECTRONICS plc
T
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Production Data, August 2012, Rev 4.1
Copyright 2012 Wolfson Microelectronics plc
DESCRIPTION
The WM9082 is a high-performance sigma-delta Class D
speaker driver. Audio input is supported using a stereo PDM
interface; clock and control-code detection circuitry supports
all of the audio and control functions via a 2-wire interface.
The digital audio interface provides excellent noise
immunity, eliminating traditional input-filtering components.
The flexible 2-wire interface minimises the PCB footprint and
simplifies software development.
The combined audio and control interface configuration is
ideal for enabling the WM9082 to be located close to the
speaker; this reduces the length of the output connections,
giving good EMC performance and removing the need for
output filter components.
The sigma-delta architecture provides good power efficiency
and improved EMI performance with respect to traditional
PWM Class D designs.
A first-order high-pass filter can be selected on the input
signal to remove DC offsets and help to prevent speaker
damage. Other features include a low-power mute state,
and output slew-rate control.
Short-circuit and thermal protection is provided.
The WM9082 is supplied in a 9-ball 1.56 x 1.46mm CSP
package, with 0.5mm ball pitch.
FEATURES
Sigma-Delta Class-D speaker driver
- 92dB SNR - ‘A’ weighted
- 2.5W into 4 (5V supply, 1% THD)
- 1.3W into 4 (3.6V supply, 1% THD)
- 1.25W into 8 (5V supply, 1% THD)
- 650mW into 8 (3.6V supply, 1% THD
Stereo PDM digital audio input
Supports 32kHz, 44.1kHz, 48kHz sample rates (128fs input)
Automatic Left/Right channel selection
First-order high pass filter (HPF)
RF noise suppression
Pop and click suppression
Programmable output slew rates for low EMI
Short-circuit and thermal protection
9-ball CSP package
APPLICATIONS
Mobile Handsets
Portable Media Players (PMP)
Notebooks / Laptop computers
LCD televisions
BLOCK DIAGRAM
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TABLE OF CONTENTS
DESCRIPTION ....................................................................................................... 1
FEATURES ............................................................................................................ 1
APPLICATIONS ..................................................................................................... 1
BLOCK DIAGRAM ................................................................................................ 1
TABLE OF CONTENTS ......................................................................................... 2
PIN CONFIGURATION .......................................................................................... 3
ORDERING INFORMATION .................................................................................. 3
PIN DESCRIPTION ................................................................................................ 3
ABSOLUTE MAXIMUM RATINGS ........................................................................ 4
RECOMMENDED OPERATING CONDITIONS ..................................................... 4
ELECTRICAL CHARACTERISTICS ..................................................................... 5
TERMINOLOGY ............................................................................................................... 6
TYPICAL PERFORMANCE ................................................................................... 7
SIGNAL TIMING REQUIREMENTS ...................................................................... 8
PDM AUDIO INTERFACE TIMING .................................................................................. 8
DEVICE DESCRIPTION ........................................................................................ 9
INTRODUCTION .............................................................................................................. 9
PDM AUDIO INTERFACE ................................................................................................ 9
DEVICE CONTROL CODES .......................................................................................... 10
INITIAL POWER-UP .................................................................................................................................. 12
CONFIGURATION EVENTS ..................................................................................................................... 12
START-UP EVENTS ................................................................................................................................. 13
STANDBY EVENTS .................................................................................................................................. 14
SHUTDOWN EVENTS .............................................................................................................................. 14
STATE TRANSITION DIAGRAM ............................................................................................................... 15
SPEAKER DRIVER ........................................................................................................ 16
RESETS AND SHUTDOWN .......................................................................................... 16
APPLICATIONS INFORMATION ........................................................................ 17
RECOMMENDED EXTERNAL COMPONENTS ............................................................ 17
PCB LAYOUT CONSIDERATIONS ............................................................................... 20
PACKAGE DIMENSIONS .................................................................................... 21
PACKAGE DIAGRAM FOR DEVICES MARKED LT9 ................................................... 21
PACKAGE DIAGRAM FOR DEVICES MARKED JC5 ................................................... 22
IMPORTANT NOTICE ......................................................................................... 23
ADDRESS: ..................................................................................................................... 23
REVISION HISTORY ........................................................................................... 24
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PIN CONFIGURATION
The WM9082 is supplied in a 9-ball CSP format. The pin configuration is illustrated below, showing
the top-down view from above the chip.
ORDERING INFORMATION
ORDER CODE TEMPERATURE RANGE PACKAGE MOISTURE
SENSITIVITY LEVEL
PEAK SOLDERING
TEMPERATURE
WM9082ECSN/R -40C to +85C 9-ball CSP
(Pb-free, tape and reel)
MSL1 260oC
Note:
Reel quantity = 5,000
PIN DESCRIPTION
PIN NO NAME TYPE DESCRIPTION
A1 SPKOUTP Analogue Output Positive BTL speaker output
A2 DNC Do not connect
A3 GND Supply Ground
B1 SPKVDD Supply Class D output driver supply
B2 SPKGND Supply Ground
B3 DVDD Supply Digital supply
C1 SPKOUTN Analogue Output Negative BTL speaker output
C2 IN2 Digital Input PDM input (CLK or Left DATA input)
C3 IN1 Digital Input PDM input (CLK or Right DATA input)
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ABSOLUTE MAXIMUM RATINGS
Absolute Maximum Ratings are stress ratings only. Permanent damage to the device may be caused by continuously
operating at or beyond these limits. Device functional operating limits and guaranteed performance specifications are given
under Electrical Characteristics at the test conditions specified.
ESD Sensitive Device. This device is manufactured on a CMOS process. It is therefore generically susceptible
to damage from excessive static voltages. Proper ESD precautions must be taken during handling and storage
of this device.
Wolfson tests its package types according to IPC/JEDEC J-STD-020B for Moisture Sensitivity to determine acceptable storage
conditions prior to surface mount assembly. These levels are:
MSL1 = unlimited floor life at <30C / 85% Relative Humidity. Not normally stored in moisture barrier bag.
MSL2 = out of bag storage for 1 year at <30C / 60% Relative Humidity. Supplied in moisture barrier bag.
MSL3 = out of bag storage for 168 hours at <30C / 60% Relative Humidity. Supplied in moisture barrier bag.
The Moisture Sensitivity Level for each package type is specified in Ordering Information.
CONDITION MIN MAX
Class D output driver supply voltage (SPKVDD) -0.3V 7.0V
Digital supply voltage (DVDD) -0.3V 2.5V
Voltage range digital inputs GND - 0.3V DVDD +0.3V
Operating temperature range, TA -40ºC +85ºC
Storage temperature after soldering -65ºC +150ºC
RECOMMENDED OPERATING CONDITIONS
PARAMETER SYMBOL MIN TYP MAX UNIT
Class D output driver supply SPKVDD 3.2 3.6 5.5 V
Digital supply DVDD 1.35 1.8 2.0 V
Ground SPKGND, GND 0 V
Note:
1. All digital and analogue grounds must always be within 0.3V of each other.
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ELECTRICAL CHARACTERISTICS
Test Conditions
SPKVDD = 3.6V, DVDD = 1.8V, SPKGND=GND = 0V, TA = +25oC, Load = 4+33µH,
1kHz signal, CLK=6.144MHz (128fs), fs=48kHz unless otherwise stated.
PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT
Speaker Driver
Signal to Noise ratio SNR A-weighted 92 dB
Idle channel noise A-weighted 66 VRMS
Total Harmonic
Distortion + Noise
THD+N PO = 625mW -70 dB
Output Power
(THD+N = 1%)
PO RL = 4, SPKVDD = 3.6V 1.3 W
RL = 4, SPKVDD = 5.0V 2.5
RL = 8, SPKVDD = 3.6V 0.65
RL = 8, SPKVDD = 5.0V 1.25
Speaker Load resistance
(see note 1)
3
Speaker Load
capacitance
(see note 1)
Direct connection to
SPKOUTP+SPKOUTN
200 pF
PSRR (SPKVDD) PSRR 200mV (peak-peak) 217Hz
Idle digital audio input while in
the ON state
70 dB
Power efficiency RL = 4, PO = 625mW,
SPKVDD = 3.6V
82 %
RL = 8, PO = 625mW,
SPKVDD = 3.6V
86
Clocking (IN1 or IN2)
CLK input fs = 48kHz 6.144 MHz
fs = 44.1kHz 5.6448
fs = 32kHz 4.096
Digital Input (IN1 or IN2)
Input high level
(see note 1)
0.7 x DVDD V
Input low level
(see note 1)
0.3 x DVDD V
Input capacitance
(see note 1)
10 pF
Input leakage -0.9 0.9 A
Other Parameters
Pop-free start-up time ‘OFF’ state to ‘ON’ state
(see Figure 3)
1 ms
Shutdown time ‘ON’ state to ‘OFF’ state
(see Figure 3)
1 ms
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PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT
Power Consumption
Quiescent current
(WM9082 in the ‘ON’
state; CLK enabled;
DATA input is idle
channel data.)
IDVDD 0.6 mA
ISPKVDD RL = 4 8 mA
RL = 8 8
Standby current
(WM9082 in the
‘STANDBY’ state; CLK
enabled; DATA input is
repeated Control Code.)
IDVDD 250 µA
ISPKVDD 200 µA
Shutdown current
(WM9082 in the OFF
state; CLK and DATA
inputs disabled.)
IDVDD 0.6 µA
ISPKVDD 0.05 µA
Note 1: Guaranteed by design; not production-tested.
TERMINOLOGY
1. Signal-to-Noise Ratio (dB) – SNR is the difference in level between a full scale output signal and the device output
noise with no signal applied, measured over a bandwidth of 20Hz to 20kHz. (No Auto-zero or Mute function is
employed).
2. Total Harmonic Distortion (dB) – THD is the difference in level between a 1kHz reference sine wave output signal and
the sum of the harmonics of the output signal. The amplitude of the fundamental frequency of the output signal is
compared to the RMS value of the sum of the harmonics and expressed as a ratio.
3. Total Harmonic Distortion plus Noise (dB) – THD+N is the difference in level between a 1kHz reference sine wave
output signal and all noise and distortion products in the audio band. The amplitude of the fundamental reference
frequency of the output signal is compared to the RMS value of all other noise and distortion products and expressed
as a ratio.
4. Power Supply Rejection Ratio (dB) – PSRR is a measure of ripple attenuation between a power supply rail and a
signal output path. With the signal path idle, a small sine wave ripple is applied to power supply rail. The amplitude of
the supply ripple is compared to the amplitude of the output signal generated and is expressed as a ratio.
5. All performance measurements are carried out with 20kHz AES17 low pass filter for distortion measurements, and an
A-weighted filter for noise measurement. Failure to use such a filter will result in higher THD and lower SNR and
Dynamic Range readings than are found in the Electrical Characteristics. The low pass filter removes out-of-band
noise; although it is not audible, it may affect dynamic specification values.
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TYPICAL PERFORMANCE
Typical speaker driver THD+N performance is shown below for 8 and 4 load conditions. Plots are shown for typical
SPKVDD supply voltage conditions. (DVDD=1.8V in all cases.)
0.00
0.01
0.10
1.00
10.00
0.10 1.00
THD + N Ratio (% )
Output Power (W)
THD+N vs. Output Power
Load = 8+ 33µH
SPKVDD=5.5V
SPKVDD=3.6V
0.00
0.01
0.10
1.00
10.00
0.10 1.00
THD + N Ratio (% )
Output Power (W)
THD+N vs. Output Power
Load = 4+ 33µH
SPKVDD=5.5V
SPKVDD=3.6V
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SIGNAL TIMING REQUIREMENTS
PDM AUDIO INTERFACE TIMING
CLK
(input)
DATA
(input)
tLH
tLSU tRH
tRSU
tCY
tCL
tCH
Test Conditions
SPKVDD=3.6V, DVDD=1.8V, SPKGND=GND=0V, TA = +25oC, unless otherwise stated.
PARAMETER SYMBOL MIN TYP MAX UNIT
PDM Audio Interface Timing
CLK cycle time tCY 140 162 250 ns
CLK pulse width high tCH 60 81 ns
CLK pulse width low tCL 60 81 ns
DATA set-up time to CLK rising edge (Left channel data) tLSU 10 ns
DATA hold time from CLK rising edge (Left channel data) tLH 7 ns
DATA set-up time to CLK falling edge (Right channel data) tRSU 10 ns
DATA hold time from CLK falling edge (Right channel data) tRH 7 ns
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DEVICE DESCRIPTION
INTRODUCTION
The WM9082 is a high performance sigma-delta Class D speaker driver designed for a range of high
performance, low-power audio applications. It is packaged in a 9-ball CSP.
The device comprises two digital input pins, which support the CLK and DATA inputs of the PDM
audio interface. Automatic Left/Right channel selection is provided using automatic detection of the
input configuration. The PDM audio interface also supports decoding of silent Control Codes which
can be used to configure the WM9082 or to select the low power, Standby operating state.
The WM9082 incorporates a selectable first-order high-pass filter for removing DC offsets and to help
prevent speaker damage. Input sample rates of 32kHz, 44.1kHz and 48kHz are supported.
The sigma-delta architecture of the Class D output driver provides good power efficiency and
improved EMI performance with respect to traditional PWM Class D designs.
The Class D speaker driver is powered from SPKVDD in the range 3.2V to 5.5V. The driver can
deliver 2.5W output into a 4 load. The WM9082 is suitable for positioning very close to the external
loudspeaker. The differential (BTL) outputs can connect directly to the loudspeaker with no other
external components required.
Short-circuit and thermal protection is also provided.
The WM9082 is supplied in a 9-ball 1.56 x 1.46mm CSP package, with 0.5mm ball pitch.
PDM AUDIO INTERFACE
The WM9082 supports a stereo PDM audio interface, comprising a CLK wire and a DATA wire. Two
channels of audio data are multiplexed on the DATA wire; the WM9082 speaker driver selects either
the Left channel data or the Right channel data depending on the hardware configuration of the
interface connection.
Each channel of PDM audio data consists of a stream of 1-bit data samples; the bit rate is 128 x fs,
where fs is the sample frequency of the received audio signal. Note that PDM is a ‘pulse density
modulation’ coding, where the signal amplitude is represented by the density of logic 1’s in any
window of consecutive data bits.
Two audio channels are interleaved on the PDM interface as illustrated in Figure 1. The Left channel
data is read at the rising edge of CLK; the Right channel data is read at the falling edge of CLK. See
“Signal Timing Requirements” for specific timing requirements.
CLK input
DATA input
(left & right channels interleaved) L R L R L R
Left channel input LLL
Right channel input RRR
Figure 1 PDM Audio Interface
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The channel selection for the WM9082 speaker driver is implemented automatically by sensing which
of the inputs pins is CLK and which pin is DATA, as defined in Table 1.
To ensure correct channel selection, it must be ensured that the DATA input is disabled whenever the
CLK input is disabled. If the DATA input signal is present when CLK is disabled, this may result in
incorrect channel selection.
INPUT CONFIGURATION SPEAKER CHANNEL
CLK = IN1 DATA = IN2 Left
CLK = IN2 DATA = IN1 Right
Table 1 PDM Channel Selection
If stereo operation is required, using two WM9082 speaker drivers, then this can be implemented very
easily, by cross-connecting the CLK and DATA wires on the two speaker drivers, as illustrated in
Figure 2.
Figure 2 Stereo PDM Operation
The channel detection is determined automatically at device start-up, and also after any period when
the CLK input has stopped.
DEVICE CONTROL CODES
When power supplies are present (see “Recommended Operating Conditions”), and audio data is
input at the audio interface, the WM9082 powers up and the Class D speaker driver is enabled. The
WM9082 selects either the Left or Right channel data as described in “PDM Audio Interface”.
The WM9082 can be controlled using specific data sequences, known as Control Codes, received
over the PDM audio interface. Each Control Code is a “zero” code when decoded as audio data.
Therefore, the Control Codes can be transmitted to the WM9082 in the form of silent audio data, but
the codes will be recognised by the WM9082 as control instructions.
The WM9082 Control Codes are defined in Table 2 and Table 3.
The Control Codes are 8-bit codes, which must be transmitted LSB first.
The Page 1 Control Codes (see Table 2) are valid when transmitted consecutively for the required
number of times. The Page 2 Control Codes (see Table 3) are valid only when preceded by the “Page
2 access” instruction (ie. Page 1, Code 6).
In most cases, the Control Codes are only valid if they are received more than 32 times consecutively
(see below for further details). For greatest reliability, however, it is recommended that the host device
always transmits Control Codes at least 64 times whenever it is desired to send a control instruction
to the WM9082.
If the WM9082 is configured to receive Left channel data, then it will only respond to Control Codes
received on the Left channel of the PDM interface. Similarly, if the WM9082 is configured to receive
Right channel data, then it will only respond to Control Codes received on the Right channel.
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ID FUNCTION DESCRIPTION CONTROL
CODE
Code 1 Start Up (3.6V SPKVDD) Fast Start-Up for default SPKVDD AA
Code 2 Standby Disable Class D output 66
Code 3 EMI control 1 Invert SR[1] F0
Code 4 32kHz mode control Select 32kHz sample rate mode 8B
Code 5 High Pass Filter control Disable 2Hz High Pass Filter 39
Code 6 Page 2 access Enable Page 2 Control Codes 56
Code 7 Reserved D1
Code 8 Reserved D2
Code 9 Start Up (3.6V SPKVDD) Start-Up for SPKVDD = 3.6V D4
Code 10 Start Up (5.0V SPKVDD) Start-Up for SPKVDD = 5.0V D8
Table 2 WM9082 Page 1 Control Codes
ID FUNCTION DESCRIPTION CONTROL
CODE
Code 1 Reserved AA
Code 2 Reserved 66
Code 3 Performance control 1 Invert PC1[0] F0
Code 4 Reserved 8B
Code 5 Reserved 39
Code 6 Reserved 56
Code 7 Reserved D1
Code 8 Reserved D2
Code 9 EMI control 2 Invert SR[0] D4
Code 10 Performance control 2 Increment PC2[1:0] D8
Table 3 WM9082 Page 2 Control Codes
The output driver slew-rate control is configurable using the SR[1] and SR[0] bits. These fields are
defined in Table 4. The slew-rate Control Code sequences are described in Table 6.
SR[1] SR[0] OUTPUT SLEW RATE
(OUTPUT RISE / FALL TIME)
0 0 5ns (Default)
0 1 10ns
1 0 20ns
1 1 40ns
Table 4 Output Slew Rate Control bits
The output driver operating mode is configurable using the PC1[0] and PC2[1:0] bits. These fields are
defined in Table 5. Selected operating mode Control Code sequences are described in Table 6.
PC1[0] PC2[1:0] DESCRIPTION
1 00 Best PSRR
1 01 (default)
1 10
1 11
0 XX Best SNR
Table 5 Operating Mode Control bits
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As noted above, the WM9082 Control Codes are only valid when they are transmitted consecutively
for the required number of times. The valid Control Codes can be used to control the operating state
of the WM9082 and also to select different operating modes.
The “Page 2 access” Control Code enables the Page 2 Control Codes for the next control code only;
the Page 1 codes will apply again for any subsequent control code(s).
The state transitions and operating modes are described below.
INITIAL POWER-UP
When a valid CLK signal is first detected on IN1 or IN2, the WM9082 powers up to the “STANDBY”
state. The WM9082 will remain in this state until a “Start-up Event” is detected, or until the CLK signal
is removed.
CONFIGURATION EVENTS
In the STANDBY state, the WM9082 can be configured (if required) using the Control Code
sequences listed in Table 6.
Note that these Control Code sequences are only valid when the WM9082 is in the STANDBY state; it
is not possible to configure the device whilst simultaneously sending audio data.
The following features are configurable in the STANDBY state:
Sample rate (33kHz, 44.1kHz or 48kHz)
Input path High Pass Filter (HPF)
Output slew rate control
Operating Mode (PSRR vs SNR control)
The cut-off frequency of the input path HPF, when enabled, is around 2Hz, assuming a 48kHz audio
sample rate (CLK = 6.144MHz).
The operating mode selections provide different options for SNR vs PSRR optimisation.
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The Control Code sequences are listed in Table 6.
DESCRIPTION CONTROL CODE
Select 32kHz sample rate 32 x Code 4
Disable the input path HPF 32 x Code 5
Select 10ns output slew rate 32 x Code 6
32 x Code 9
Select 20ns output slew rate 32 x Code 3
Select 40ns output slew rate 32 x Code 3
32 x Code 6
32 x Code 9
Select ‘Best PSRR’ mode 32 x Code 6
32 x Code 10
32 x Code 6
32 x Code 10
32 x Code 6
32 x Code 10
Select ‘Best SNR’ mode 32 x Code 6
32 x Code 3
Table 6 WM9082 Configuration Events
If none of these Control Code sequences is received, then the WM9082 is configured for the following
default operating conditions:
Sample rate is 44.1kHz or 48kHz
Input path High Pass Filter (HPF) enabled
Output slew rate is 10ns
Default PSRR and SNR (see “Electrical Characteristics”)
Note that the default operating conditions are only restored on power-up or following a period when
the CLK input is stopped.
START-UP EVENTS
The WM9082 Class D output is enabled whenever PDM audio data is detected at the input pins, or
when a valid Start-Up Control Code is detected. The WM9082 Start-Up is selected under any of the
conditions described in Table 7. Each of these conditions results in a transition to the “ON” state.
Note that, if SPKVDD > 4.3V, then it is recommended to start up the WM9082 using Code 10; this
ensures that the device is optimally configured for the higher SPKVDD level.
Note that, when the start-up transition occurs as a result of PDM audio data, then the WM9082 will be
enabled in whichever mode had previously been selected (if any). In the case where the “ON” state
has not previously been selected, then the default (SPKVDD = 3.6V) mode is chosen.
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CONDITION DESCRIPTION
4 x Code 1 Fast start-up for default SPKVDD condition (SPKVDD = 3.6V)
32 x Code 9 Start-up for SPKVDD = 3.6V
32 x Code 10 Start-up for SPKVDD = 5.0V
PDM audio data Fast start-up
Table 7 WM9082 Start-Up Events
STANDBY EVENTS
The WM9082 Class D output is disabled whenever the PDM input data is interrupted, or when a valid
Standby Control Code is detected. The WM9082 Standby transition is selected during normal
operation (ie. from the “ON” state”) under any of the conditions described in Table 8. Each of these
conditions results in a transition to the “STANDBY” state.
CONDITION DESCRIPTION
32 x Code 2 Standby command - selects STANDBY state
64 x Any Control Code Selects STANDBY state
Error condition Selects STANDBY state
(An error condition is detected if >24 consecutive 1’s or >24
consecutive 0’s is received on the PDM audio interface.)
Table 8 WM9082 Standby Events
Note that repeated instances of any Control Code will not cause more than one state transition until
audio data or a different Control Code has been received. This prevents the WM9082 from cycling
between the “ON” state and the “STANDBY” state in the event of repeated Control Codes.
SHUTDOWN EVENTS
If the CLK input is not present at any time, this results in a transition to the “OFF” state. The WM9082
will remain in the “OFF” state until the CLK input restarts.
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STATE TRANSITION DIAGRAM
The WM9082 operating states and transitions are illustrated in Figure 3.
Figure 3 State Transition Diagram
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SPEAKER DRIVER
The speaker outputs SPKOUTP and SPKOUTN operate in a BTL configuration. These pins provide a
differential output for direct connection to the loudspeaker. In a typical application, no other external
components are required for the loudspeaker connection.
The sigma-delta architecture of the Class D driver is more linear and power efficient than traditional
PWM implementations, resulting in reduced power consumption and improved EMI characteristics.
The speaker driver is disabled during start-up and following receipt of selected Control Codes which
can be used to configure the WM9082. The driver is automatically re-enabled on receipt of any audio
data.
RESETS AND SHUTDOWN
A power on reset circuit ensures correct start-up and shut-down when the DVDD supply rail is
enabled or disabled.
The WM9082 is held in the “OFF” state when there is no CLK signal detected on the IN1 or IN2 pins;
the Shutdown current in the “OFF” state is noted in the “Electrical Characteristics” section.
Short circuit and thermal protection is also provided. In the event of an output short-circuit or an over-
temperature condition, the WM9082 will protect itself by disabling the Class D speaker driver. The
WM9082 will automatically recover and continue normal operation when the fault condition is cleared.
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APPLICATIONS INFORMATION
RECOMMENDED EXTERNAL COMPONENTS
POWER SUPPLY DECOUPLING
Electrical coupling exists particularly in digital logic systems where switching in one sub-system
causes fluctuations on the power supply. This effect occurs because the inductance of the power
supply acts in opposition to the changes in current flow that are caused by the logic switching. The
resultant variations (or ‘spikes’) in the power supply voltage can cause malfunctions and unintentional
behaviour in other components. A decoupling (or ‘bypass’) capacitor can be used as an energy
storage component which will provide power to the decoupled circuit for the duration of these power
supply variations, protecting it from malfunctions that could otherwise arise.
Coupling also occurs in a lower-frequency form when ripple is present on the power supply rail
caused by changes in the load current or by limitations of the power supply regulation method. In
audio components such as the WM9082, these variations can alter the performance of the signal
path, leading to degradation in signal quality. A decoupling (or ‘bypass’) capacitor can be used to filter
these effects, by presenting the ripple voltage with a low impedance path that does not affect the
circuit to be decoupled.
These coupling effects are addressed by placing a capacitor between the supply rail and the
corresponding ground reference. In the case of systems comprising multiple power supply rails,
decoupling should be provided on each rail.
The recommended power supply decoupling capacitors for WM9082 are listed below in Table 9.
POWER SUPPLY DECOUPLING CAPACITOR
DVDD 0.1F ceramic
SPKVDD 4.7F ceramic
Table 9 Power Supply Decoupling Capacitors
All decoupling capacitors should be placed as close as possible to the WM9082 device.
Due to the wide tolerance of many types of ceramic capacitors, care must be taken to ensure that the
selected components provide the required capacitance across the required temperature and voltage
ranges in the intended application. For most application the use of ceramic capacitors with capacitor
dielectric X5R is recommended.
CLASS D SPEAKER CONNECTIONS
The WM9082 incorporates a Class D speaker driver, which offers high amplifier efficiency at large
signal levels. As the Class D output is a sigma-delta modulated signal, the choice of speakers and
tracking of signals is important for ensuring good performance and reducing EMI.
The efficiency of the speaker drivers is affected by the series resistance between the WM9082 and
the speaker (e.g. PCB track loss and inductor ESR) as shown in Figure 4. This resistance should be
as low as possible to maximise efficiency.
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Figure 4 Speaker Connection Losses
The Class D output requires external filtering in order to recreate the audio signal. This may be
implemented using a 2nd order LC filter, or else may be achieved by using a loudspeaker whose
internal inductance provides the required filter response. An LC filter should be used if the
loudspeaker characteristics are unknown or unsuitable, or if the length of the loudspeaker connection
is likely to lead to EMI problems.
A suitable LC filter implementation is illustrated in Figure 5.
Figure 5 Class D Output Filter Components
A simple equivalent circuit of a loudspeaker consists of a serially connected resistor and inductor, as
shown in Figure 6. This circuit provides a low pass filter for the speaker output. If the loudspeaker
characteristics are suitable, then the loudspeaker itself can be used in place of the filter components
described earlier. This is known as ‘filterless’ operation.
Figure 6 Speaker Equivalent Circuit for Filterless Operation
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For filterless Class D operation, it is important to ensure that a speaker with suitable inductance is
chosen. For example, if we know the speaker impedance is 8 and the desired cut-off frequency is
20kHz, then the optimum speaker inductance may be calculated as:
8 loudspeakers typically have an inductance in the range 20H to 100H, however, it should be
noted that a loudspeaker inductance will not be constant across the relevant frequencies for Class D
operation (up to and beyond the Class D switching frequency).
The Class D outputs of the WM9082 operate at much higher frequencies than is recommended for
most speakers; care should be taken to ensure that the cut-off frequency of the loudspeaker’s filtering
is low enough to suppress the high frequency energy of the Class D switching and, in so doing, to
prevent speaker damage.
A simple test can be used to confirm if the loudspeaker is compatible with filterless operation. Under
quiescent input conditions (idle digital audio input while in the ON state), the SPKVDD current is
measured with the speaker disconnected, and measured again with the speaker connected. If the
SPKVDD current increases by more than 10mA when the speaker is connected, then the speaker
alone is not effective as a filter, and it is recommended to consider changing the speaker or adding
LC filter components.
RECOMMENDED EXTERNAL COMPONENTS DIAGRAM
Figure 7 provides a summary of recommended external components for WM9082. Note that the
actual requirements may differ according to the specific target application.
Figure 7 WM9082 Recommended External Components Diagram
WM9082 Production Data
w PD, August 2012, Rev 4.1
20
PCB LAYOUT CONSIDERATIONS
Poor PCB layout will degrade the performance and be a contributory factor in EMI, ground bounce
and resistive voltage losses. All external components should be placed as close to the WM9082
device as possible, with current loop areas kept as small as possible.
CLASS D LOUDSPEAKER CONNECTION
Long, exposed PCB tracks or connection wires will emit EMI. The distance between the WM9082 and
the loudspeaker should therefore be kept as short as possible. Where speakers are connected to the
PCB via a cable form, it is recommended that a shielded twisted pair cable is used. The shield should
be connected to the main system, with care taken to ensure ground loops are avoided.
Further reduction in EMI can be achieved using PCB ground (or VDD) planes and also by using
passive LC components to filter the Class D switching waveform. When passive filtering is used, low
ESR components should be chosen in order to minimise the series resistance between the WM9082
and the speaker, maximising the power efficiency.
LC passive filtering will usually be effective at reducing EMI at frequencies up to around 30MHz. To
reduce emissions at higher frequencies, ferrite beads can also be used. These should be positioned
as close to the device as possible.
These techniques for EMI reduction are illustrated in Figure 8.
EMI
LOW ESR
LOW ESR
Long, exposed tracks emit EMI
Short connection wires will reduce EMI emission
Shielding using PCB ground (or VDD) planes
will reduce EMI emission
LC filtering will reduce EMI emission
up to around 30MHz
Ferrite beads will reduce EMI emission
at frequencies above 30MHz.
WM9082
WM9082
WM9082
WM9082
WM9082
SPKOUTP
SPKOUTN
SPKOUTP
SPKOUTN
SPKOUTP
SPKOUTN
SPKOUTP
SPKOUTN
SPKOUTP
SPKOUTN
Figure 8 EMI Reduction Techniques
Production Data WM9082
w PD, August 2012, Rev 4.1
21
PACKAGE DIMENSIONS
PACKAGE DIAGRAM FOR DEVICES MARKED LT9
DM085.B
B: 9 BALL W-CSP PACKAGE 1.560 X 1.460 X 0.635mm BODY, 0.50 mm BALL PITCH
NOTES:
1. PRIMARY DATUM -Z- AND SEATING PLANE ARE DEFINED BY THE SPHERICAL CROWNS OF THE SOLDER BALLS.
2. A1 CORNER IS IDENTIFIED BY INK/LASER MARK ON TOP PACKAGE.
3. ‘e’ REPRESENTS THE BASIC SOLDER BALL GRID PITCH.
4. THIS DRAWING IS SUBJECT TO CHANGE WITHOUT NOTICE.
5. FOLLOWS JEDEC DESIGN GUIDE MO-211-C.
A1 0.230
D
D1
E
E1
e
1.000 BSC
1.460
0.275
1.000 BSC
0.500 BSC
1.560
Dimensions (mm)
Symbols
MIN NOM MAX NOTE
A0.635
A2 0.388 0.400 0.412
3
f1
0.652
0.618
0.235 0.240
0.225
h0.320
A1
CORNER
TOP VIEW
E
D
2
DETAIL 2
DETAIL 2
A
A2
A1
Z
1
SOLDER BALL
E1
A
DETAIL 1
C
B
e
e
BOTTOM VIEW
132
f1
f2
h
3
D1
0.05
4 X
4
4
f2
DETAIL 1
1.550
1.450 1.470
1.570
WM9082 Production Data
w PD, August 2012, Rev 4.1
22
PACKAGE DIAGRAM FOR DEVICES MARKED JC5
DM085.C
B: 9 BALL W-CSP PACKAGE 1.570 X 1.470 X 0.649mm BODY, 0.50 mm BALL PITCH
NOTES:
1. PRIMARY DATUM -Z- AND SEATING PLANE ARE DEFINED BY THE SPHERICAL CROWNS OF THE SOLDER BALLS.
2. A1 CORNER IS IDENTIFIED BY INK/LASER MARK ON TOP PACKAGE.
3. ‘e’ REPRESENTS THE BASIC SOLDER BALL GRID PITCH.
4. THIS DRAWING IS SUBJECT TO CHANGE WITHOUT NOTICE.
5. FOLLOWS JEDEC DESIGN GUIDE MO-211-C.
A1 0.212
D
D1
E
E1
e
1.000 BSC
1.470
0.273
1.000 BSC
0.500 BSC
1.570
Dimensions (mm)
Symbols
MIN NOM MAX NOTE
A0.649
A2 0.387 0.400 0.413
3
f1
0.688
0.610
0.249 0.286
0.223
h0.311
A1
CORNER
TOP VIEW
E
D
2
DETAIL 2
DETAIL 2
A
A2
A1
Z
1
SOLDER BALL
E1
A
DETAIL 1
C
B
e
e
BOTTOM VIEW
13 2
f1
f2
h
3
D1
0.0254 X
4
4
f2
DETAIL 1
1.545
1.445 1.495
1.595
0.261 0.361
Production Data WM9082
w PD, August 2012, Rev 4.1
23
IMPORTANT NOTICE
Wolfson Microelectronics plc (“Wolfson”) products and services are sold subject to Wolfson’s terms and conditions of sale,
delivery and payment supplied at the time of order acknowledgement.
Wolfson warrants performance of its products to the specifications in effect at the date of shipment. Wolfson reserves the
right to make changes to its products and specifications or to discontinue any product or service without notice. Customers
should therefore obtain the latest version of relevant information from Wolfson to verify that the information is current.
Testing and other quality control techniques are utilized to the extent Wolfson deems necessary to support its warranty.
Specific testing of all parameters of each device is not necessarily performed unless required by law or regulation.
In order to minimize risks associated with customer applications, the customer must use adequate design and operating
safeguards to minimise inherent or procedural hazards. Wolfson is not liable for applications assistance or customer
product design. The customer is solely responsible for its selection and use of Wolfson products. Wolfson is not liable for
such selection or use nor for use of any circuitry other than circuitry entirely embodied in a Wolfson product.
Wolfson’s products are not intended for use in life support systems, appliances, nuclear systems or systems where
malfunction can reasonably be expected to result in personal injury, death or severe property or environmental damage.
Any use of products by the customer for such purposes is at the customer’s own risk.
Wolfson does not grant any licence (express or implied) under any patent right, copyright, mask work right or other
intellectual property right of Wolfson covering or relating to any combination, machine, or process in which its products or
services might be or are used. Any provision or publication of any third party’s products or services does not constitute
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belong to the respective third party owner.
Reproduction of information from Wolfson datasheets is permissible only if reproduction is without alteration and is
accompanied by all associated copyright, proprietary and other notices (including this notice) and conditions. Wolfson is
not liable for any unauthorisedٛ alteration of such information or for any reliance placed thereon.
Any representations made, warranties given, and/or liabilities accepted by any person which differ from those contained in
this datasheet or in Wolfson’s standard terms and conditions of sale, delivery and payment are made, given and/or
accepted at that person’s own risk. Wolfson is not liable for any such representations, warranties or liabilities or for any
reliance placed thereon by any person.
ADDRESS:
Wolfson Microelectronics plc
26 Westfield Road
Edinburgh
EH11 2QB
United Kingdom
Tel :: +44 (0)131 272 7000
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Email :: sales@wolfsonmicro.com
WM9082 Production Data
w PD, August 2012, Rev 4.1
24
REVISION HISTORY
DATE REV DESCRIPTION OF CHANGES PAGE CHANGED BY
05/07/10 1.0
First Release
20/04/11 2.0
Product status updated to preliminary technical data
21/04/11 2.0
Updated pinout changing VREFC to DNC. All associated diagrams
and tables also updated to reflect the change
1, 4, 16,
18
WF
28/04/11 2.0
PSRR typical electrical characteristics values added 5 BM
03/05/11 2.0
In Description, removed ‘The recommended configuration requires
only 3 external capacitors’
1 WF
12/08/11 2.1/2.2
Electrical Characteristics updated.
Additional Control Codes defined for slew rate control &
performance mode.
Updates to filterless speaker description & recommendations
PH
15/09/11 2.2
Electrical Characteristics updated
Default slew rate / operating mode conditions updated
PH
25/10/11 3.0
Product status updated to pre-production JMacD
18/05/12 4.0
Electrical Characteristics updated
Typical performance graphs added
PH
10/08/12 4.1
Package Diagram DM085C added. JMacD
