2 × 2W Filterless Class-D
Stereo Audio Amplifier
SSM2356
The SSM2356 features a high efficiency, low noise modulation
scheme that requires no external LC output filters. The modulation
continues to provide high efficiency even at low output power.
It operates with 92% efficiency at 1.4 W into 8 Ω or 85% efficiency
at 2.0 W into 4 Ω from a 5.0 V supply and has an SNR of >103 dB.
FEATURES
Filterless stereo Class-D amplifier with Σ-Δ modulation
No sync necessary when using multiple Class-D amplifiers
from Analog Devices, Inc.
2 × 2W into 4 Ω load and 2x1.4 W into 8 Ω load at 5.0 V
supply with <1% total harmonic distortion (THD + N)
92% efficiency at 5.0 V, 1.4 W into 8 Ω speaker
>103 dB signal-to-noise ratio (SNR)
Single-supply operation from 2.5 V to 5.5 V
20 nA shutdown current; left/right channel control
Short-circuit and thermal protection
Available in a 16-ball, 1.66 mm × 1.66 mm WLCSP
Pop-and-click suppression
Built-in resistors that reduce board component count
User-selectable 6 dB or 18 dB gain setting
User-selectable ultralow EMI emission mode
Spread-spectrum pulse density modulation is used to provide
lower EMI-radiated emissions compared with other Class-D
architectures. The SSM2356 includes an optional modulation
select pin (ultralow EMI emission mode) that significantly
reduces the radiated emissions at the Class-D outputs, particularly
above 100 MHz.
The SSM2356 has a micropower shutdown mode with a typical
shutdown current of 20 nA. Shutdown is enabled by applying
a logic low to the SDNR and SDNL pins. The device also
includes pop-and-click suppression circuitry that minimizes
voltage glitches at the output during turn-on and turn-off,
reducing audible noise on activation and deactivation.
APPLICATIONS
Mobile phones
MP3 players
Portable gaming
Portable electronics
The fully differential input of the SSM2356 provides excellent
rejection of common-mode noise on the input. Input coupling
capacitors can be omitted if the dc input common-mode voltage
is approximately VDD/2. The preset gain of SSM2356 can be
selected between 6 dB and 18 dB with no external components
and no change to the input impedance. Gain can be further
reduced to a user-defined setting by inserting series external
resistors at the inputs.
GENERAL DESCRIPTION
The SSM2356 is a fully integrated, high efficiency, stereo Class-D
audio amplifier. It is designed to maximize performance for
mobile phone applications. The application circuit requires
a minimum of external components and operates from a single
2.5 V to 5.5 V supply. It is capable of delivering 2 × 2W of continuous output power with <1% THD + N driving a 4 Ω load from a
5.0 V supply.
The SSM2356 is specified over the commercial temperature range
(−40°C to +85°C). It has built-in thermal shutdown and output
short-circuit protection. It is available in a 16-ball, 1.66 mm ×
1.66 mm wafer level chip scale package (WLCSP).
FUNCTIONAL BLOCK DIAGRAM
VBATT
2.5V TO 5.5V
10µF
0.1µF
RIGHT IN+
SSM2356
GAIN
CONTROL
INR+
RIGHT IN–
22nF1
SHUTDOWN–R
VDD
INR– 80kΩ
22nF1
LEFT IN+
BIAS
SDNL
22nF1
INTERNAL
OSCILLATOR
FET
DRIVER
EDGE
CONTROL
80kΩ
GAIN
CONTROL
INL+
LEFT IN–
OUTR+
MODULATOR
(Σ-Δ)
BIAS
SDNR
SHUTDOWN–L
VDD
80kΩ
INL– 80kΩ
OUTR–
EDGE
EMISSION
CTRL
OUTL+
MODULATOR
(Σ-Δ)
GND
GAIN
GAIN
GAIN = 6dB OR 18dB
1 INPUT CAPS ARE OPTIONAL IF INPUT DC COMMON-MODE
VOLTAGE IS APPROXIMATELY VDD/2.
FET
DRIVER
OUTL–
GND
08084-001
22nF1
Figure 1.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2009 Analog Devices, Inc. All rights reserved.
SSM2356
TABLE OF CONTENTS
Features .............................................................................................. 1 Applications Information .............................................................. 13 Applications ....................................................................................... 1 Overview ..................................................................................... 13 General Description ......................................................................... 1 Gain Selection ............................................................................. 13 Functional Block Diagram .............................................................. 1 Pop-and-Click Suppression ...................................................... 13 Revision History ............................................................................... 2 EMI Noise.................................................................................... 13 Specifications..................................................................................... 3 Output Modulation Description .............................................. 14 Absolute Maximum Ratings............................................................ 4 Layout .......................................................................................... 14 Thermal Resistance ...................................................................... 4 Input Capacitor Selection .......................................................... 14 ESD Caution .................................................................................. 4 Proper Power Supply Decoupling ............................................ 14 Pin Configuration and Function Descriptions ............................. 5 Outline Dimensions ....................................................................... 15 Typical Performance Characteristics ............................................. 6 Ordering Guide .......................................................................... 15 Typical Application Circuits.......................................................... 12 REVISION HISTORY
5/09—Revision 0: Initial Version
Rev. 0 | Page 2 of 16
SSM2356
SPECIFICATIONS
VDD = 5.0 V, TA = 25oC, RL = 8 Ω +33 μH, EDGE = GND, Gain = 6 dB, unless otherwise noted.
Table 1.
Parameter
DEVICE CHARACTERISTICS
Output Power/Channel
Efficiency
Symbol
Conditions
PO
RL = 8 Ω, THD = 1%, f = 1 kHz, 20 kHz BW, VDD = 5.0 V
RL = 8 Ω, THD = 1%, f = 1 kHz, 20 kHz BW, VDD = 3.6 V
RL = 8 Ω, THD = 10%, f = 1 kHz, 20 kHz BW, VDD = 5.0 V
RL = 8 Ω, THD = 10%, f = 1 kHz, 20 kHz BW, VDD = 3.6 V
RL = 4 Ω, THD = 1%, f = 1 kHz, 20 kHz BW, VDD = 5.0 V
RL = 4 Ω, THD = 1%, f = 1 kHz, 20 kHz BW, VDD = 3.6 V
RL = 4 Ω, THD = 10%, f = 1 kHz, 20 kHz BW, VDD = 5.0 V
RL = 4 Ω, THD = 10%, f = 1 kHz, 20 kHz BW, VDD = 3.6 V
PO = 1.4 W, 8 Ω, VDD = 5.0 V, EDGE = GND
(normal, low EMI mode)
PO = 1.4 W, 8 Ω, VDD = 5.0 V, EDGE = VDD
(ultralow EMI mode)
PO = 1 W into 8 Ω, f = 1 kHz, VDD = 5.0 V
PO = 0.5 W into 8 Ω, f = 1 kHz, VDD = 3.6 V
η
Total Harmonic Distortion + Noise
THD + N
Input Common-Mode Voltage Range
Common-Mode Rejection Ratio
Channel Separation
Average Switching Frequency
Differential Output Offset Voltage
POWER SUPPLY
Supply Voltage Range
Power Supply Rejection Ratio
VCM
CMRRGSM
XTALK
fSW
VOOS
Typ
W
W
W
W
W
W
W
W
%
90
%
0.004
0.004
%
%
V
dB
dB
kHz
mV
Supply Current (stereo)
Shutdown Current
ISD
VRIPPLE = 100 mV at 217 Hz, inputs ac GND, CIN = 0.1 μF
VIN = 0 V, no load, VDD = 5.0 V
VIN = 0 V, no load, VDD = 3.6 V
VIN = 0 V, no load, VDD = 2.5 V
VIN = 0 V, load = 8 Ω + 33 μH, VDD = 5.0 V
VIN = 0 V, load = 8 Ω + 33 μH, VDD = 3.6 V
VIN = 0 V, load = 8 Ω + 33 μH, VDD = 2.5 V
SDNR = SDNL= GND
GAIN = VDD
GAIN = GND
SDNR = SDNL = VDD; GAIN = GND or VDD
18
6
80
dB
dB
kΩ
SDNR/SDNL rising edge from GND to VDD
SDNR/SDNL falling edge from VDD to GND
SDNR/SDNL = GND
1.35
0.35
7
5
>100
V
V
ms
μs
kΩ
29
μVrms
100
dB
Input Impedance
Gain
Gain
ZIN
SHUTDOWN CONTROL
Input Voltage High
Input Voltage Low
Turn-On Time
Turn-Off Time
Output Impedance
VIH
VIL
tWU
tSD
ZOUT
NOISE PERFORMANCE
Output Voltage Noise
en
Signal-to-Noise Ratio
SNR
Guaranteed from PSRR test
VDD = 2.5 V to 5.0 V, dc input floating
VDD − 1
55
78
300
2.0
Gain = 6 dB
VDD = 3.6 V, f = 20 Hz to 20 kHz, inputs are ac grounded,
Gain = 6 dB, A-weighted
PO = 1.4 W, RL = 8 Ω
2.5
70
Unit
1.42
0.75
1.8
0.94
2.0
1.3
2.5 1
1.7
92
1.0
VCM = 2.5 V ± 100 mV at 217 Hz, output referred
PO = 100 mW, f = 1 kHz
Max
VDD
PSRR
(DC)
PSRRGSM
ISY
GAIN CONTROL
Closed-Loop Gain
1
Min
85
5.5
V
dB
60
5.75
4.9
4.7
5.5
5.1
4.5
20
dB
mA
mA
mA
mA
mA
mA
nA
Note that, although the SSM2356 has good audio quality above 2 W per channel, continuous output power beyond 2 W per channel must be avoided due to device
packaging limitations.
Rev. 0 | Page 3 of 16
SSM2356
ABSOLUTE MAXIMUM RATINGS
Absolute maximum ratings apply at 25°C, unless otherwise noted.
THERMAL RESISTANCE
Table 2.
θJA (junction to air) is specified for the worst-case conditions,
that is, a device soldered in a circuit board for surface-mount
packages. θJA and θJB (junction to board) are determined
according to JESD51-9 on a 4-layer printed circuit board (PCB)
with natural convection cooling.
Parameter
Supply Voltage
Input Voltage
Common-Mode Input Voltage
ESD Susceptibility
Storage Temperature Range
Operating Temperature Range
Junction Temperature Range
Lead Temperature Range
(Soldering, 60 sec)
Rating
6V
VDD
VDD
4 kV
−65°C to +150°C
−40°C to +85°C
−65°C to +165°C
300°C
Table 3. Thermal Resistance
Package Type
16-ball, 1.66 mm × 1.66 mm WLCSP
ESD CAUTION
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Rev. 0 | Page 4 of 16
θJA
66
θJB
19
Unit
°C/W
SSM2356
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
BALL A1
INDICATOR
2
1
3
4
OUTL+ VDD
VDD OUTR+
OUTL– GND
GND OUTR–
A
B
SDNL EDGE GAIN SDNR
C
INL+
INL–
INR–
INR+
TOP VIEW
(BALL SIDE DOWN)
Not to Scale
08084-002
D
Figure 2. Pin Configuration (Top Side View)
Table 4. Pin Function Descriptions
Bump
A1
B1
C1
Mnemonic
OUTL+
OUTL−
SDNL
Description
Noninverting Output for Left Channel.
Inverting Output for Left Channel.
Shutdown, Left Channel. Active low digital input.
D1
D2
C4
C3
D3
D4
B2
B4
INL+
INL−
SDNR
GAIN
INR−
INR+
GND
OUTR−
Noninverting Input for Left Channel.
Inverting Input for Left Channel.
Shutdown, Right Channel. Active low digital input.
Gain select between 6 dB and 18 dB.
Inverting Input for Right Channel.
Noninverting Input for Right Channel.
Ground.
Inverting Output for Right Channel.
A4
B3
A2
A3
C2
OUTR+
GND
VDD
VDD
EDGE
Noninverting Output for Right Channel.
Ground.
Power Supply.
Power Supply.
Edge Control (Low Emission Mode); active high digital input.
Rev. 0 | Page 5 of 16
SSM2356
TYPICAL PERFORMANCE CHARACTERISTICS
100
100
RL = 8Ω + 33µH
GAIN = 6dB
VDD = 2.5V
10
VDD = 2.5V
10
1
THD + N (%)
THD + N (%)
RL = 4Ω + 15µH
GAIN = 18dB
VDD = 3.6V
0.1
VDD = 5V
0.01
1
VDD = 3.6V
0.1
0.01
0.01
0.1
1
10
OUTPUT POWER (W)
0.001
0.0001
VDD = 3.6V
VDD = 2.5V
10
0.1
1
10
100k
Figure 6. THD + N vs. Output Power into 4 Ω, AV = 18 dB
100
RL = 8Ω + 33µH
GAIN = 18dB
0.01
OUTPUT POWER (W)
Figure 3. THD + N vs. Output Power into 8 Ω, AV = 6 dB
100
0.001
08084-104
0.001
08084-101
0.001
0.0001
08084-105
VDD = 5V
10
VDD = 5V
GAIN = 6dB
RL = 8Ω + 33µH
THD + N (%)
THD + N (%)
1
1
0.1
1W
0.1
0.25W
0.01
VDD = 5V
0.01
0.001
0.5W
0.001
0.01
0.1
1
10
OUTPUT POWER (W)
0.0001
10
08084-102
0.001
0.0001
100
VDD = 2.5V
VDD = 5V
GAIN = 18dB
RL = 8Ω + 33µH
10
THD + N (%)
1
VDD = 3.6V
0.1
1
1W
0.1
0.01
0.5W
VDD = 5V
0.001
0.0001
0.001
0.01
0.1
1
OUTPUT POWER (W)
10
Figure 5. THD + N vs. Output Power into 4 Ω, AV = 6 dB
0.001
10
100
0.25W
1k
10k
100k
FREQUENCY (Hz)
Figure 8. THD + N vs. Frequency, VDD = 5 V, RL = 8 Ω, AV = 18 dB
Rev. 0 | Page 6 of 16
08084-106
0.01
08084-103
THD + N (%)
10k
Figure 7. THD + N vs. Frequency, VDD = 5 V, RL = 8 Ω, AV = 6 dB
RL = 4Ω + 15µH
GAIN = 6dB
10
1k
FREQUENCY (Hz)
Figure 4. THD + N vs. Output Power into 8 Ω, AV = 18 dB
100
100
SSM2356
100
VDD = 5V
GAIN = 6dB
RL = 4Ω + 15µH
10
10
1
1
THD + N (%)
THD + N (%)
100
2W
0.1
0.01
VDD = 3.6V
GAIN = 18dB
RL = 8Ω + 33µH
0.5W
0.1
0.01
0.5W
0.125W
0.25W
100
1k
10k
100k
FREQUENCY (Hz)
0.001
10
08084-107
0.001
10
100
10
10
1
1
THD + N (%)
THD + N (%)
10k
100k
Figure 12. THD + N vs. Frequency, VDD = 3.6 V, RL = 8 Ω, AV = 18 dB
VDD = 5V
GAIN = 18dB
RL = 4Ω + 15µH
2W
0.5W
0.1
1k
FREQUENCY (Hz)
Figure 9. THD + N vs. Frequency, VDD = 5 V, RL = 4 Ω, AV = 6 dB
100
100
08084-110
1W
VDD = 3.6V
GAIN = 6dB
RL = 4Ω + 15µH
1W
0.1
0.25W
0.01
0.01
1W
1k
10k
100k
FREQUENCY (Hz)
1
1
THD + N (%)
10
0.5W
0.125W
10k
100k
VDD = 3.6V
GAIN = 18dB
RL = 4Ω + 15µH
0.1
1W
0.25W
0.01
0.5W
0.001
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 11. THD + N vs. Frequency, VDD = 3.6 V, RL = 8 Ω, AV = 6 dB
0.001
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 14. THD + N vs. Frequency, VDD = 3.6 V, RL = 4 Ω, AV = 18 dB
Rev. 0 | Page 7 of 16
08084-112
0.25W
08084-109
THD + N (%)
100
10
0.01
1k
Figure 13. THD + N vs. Frequency, VDD = 3.6 V, RL = 4 Ω, AV = 6 dB
VDD = 3.6V
GAIN = 6dB
RL = 8Ω + 33µH
0.1
100
FREQUENCY (Hz)
Figure 10. THD + N vs. Frequency, VDD = 5 V, RL = 8 Ω, AV = 18 dB
100
0.5W
08084-111
100
0.001
10
08084-108
0.001
10
SSM2356
100
VDD = 2.5V
GAIN = 6dB
RL = 8Ω + 33µH
10
10
1
1
THD + N (%)
THD + N (%)
100
0.25W
0.1
VDD = 2.5V
GAIN = 18dB
RL = 4Ω + 15µH
0.5W
0.1
1.25W
0.0625W
0.01
0.01
100
1k
10k
100k
FREQUENCY (Hz)
0.001
10
08084-113
7.0
ISY FOR BOTH CHANNELS
GAIN = 6dB
0.25W
0.0625W
0.01
4Ω + 15µH
5.5
8Ω + 33µH
5.0
NO LOAD
4.5
0.125W
1k
10k
100k
FREQUENCY (Hz)
4.0
2.5
08084-114
100
6.0
3.0
3.5
4.0
4.5
5.0
5.5
08084-117
SUPPLY CURRENT (mA)
THD + N (%)
1
5.5
SUPPLY VOLTAGE (V)
Figure 16. THD + N vs. Frequency, VDD = 2.5 V, RL = 8 Ω, AV = 18 dB
100
100k
6.5
10
0.001
10
10k
Figure 18. THD + N vs. Frequency, VDD = 2.5 V, RL = 4 Ω, AV = 18 dB
VDD = 2.5V
GAIN = 18dB
RL = 8Ω + 33µH
0.1
1k
FREQUENCY (Hz)
Figure 15. THD + N vs. Frequency, VDD = 2.5 V, RL = 8 Ω, AV = 6 dB
100
100
08084-118
0.001
10
08084-116
0.25W
0.125W
Figure 19. Supply Current vs. Supply Voltage, AV = 6 dB
7.5
VDD = 2.5V
GAIN = 6dB
RL = 4Ω + 15µH
ISY FOR BOTH CHANNELS
GAIN = 18dB
7.0
SUPPLY CURRENT (mA)
10
1
0.1
0.25W
6.5
4Ω + 15µH
6.0
8Ω + 33µH
5.5
5.0
NO LOAD
0.01
4.5
0.125W
0.001
10
100
1k
10k
100k
FREQUENCY (Hz)
08084-115
THD + N (%)
0.5W
Figure 17. THD + N vs. Frequency, VDD = 2.5 V, RL = 4 Ω, AV = 6 dB
4.0
2.5
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
Figure 20. Supply Current vs. Supply Voltage, AV = 18 dB
Rev. 0 | Page 8 of 16
SSM2356
2.0
3.5
f = 1kHz
1.8 GAIN = 6dB
RL = 8Ω + 33µH
f = 1kHz
GAIN = 18dB
3.0 RL = 4Ω + 15µH
1.4
OUTPUT POWER (W)
OUTPUT POWER (W)
1.6
1.2
10%
1.0
0.8
1%
0.6
2.5
2.0
10%
1.5
1%
1.0
0.4
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
0
2.5
08084-119
Figure 21. Maximum Output Power vs. Supply Voltage, RL = 8 Ω, AV = 6 dB
4.0
4.5
5.0
Figure 24. Maximum Output Power vs. Supply Voltage, RL = 4 Ω, AV = 18 dB
100
f = 1kHz
GAIN = 18dB
1.6
RL = 8Ω + 33µH
VDD = 2.5V
90
VDD = 5V
VDD = 3.6V
80
1.4
70
1.2
EFFICIENCY (%)
OUTPUT POWER (W)
3.5
SUPPLY VOLTAGE (V)
1.8
10%
1.0
0.8
1%
0.6
60
50
40
30
0.4
20
0.2
GAIN = 6dB
RL = 8Ω + 33µH
POUT FOR BOTH CHANNELS
10
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
0
08084-120
0
2.5
3.0
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4
OUTPUT POWER (W)
Figure 22. Maximum Output Power vs. Supply Voltage, RL = 8 Ω, AV = 18 dB
08084-123
0
2.5
08084-122
0.5
0.2
Figure 25. Efficiency vs. Output Power into 8 Ω
3.5
100
f = 1kHz
GAIN = 6dB
3.0 RL = 4Ω + 15µH
90
70
EFFICIENCY (%)
OUTPUT POWER (W)
80
2.5
2.0
10%
1.5
1%
VDD = 2.5V
VDD = 5V
VDD = 3.6V
60
50
40
30
1.0
20
3.0
3.5
4.0
SUPPLY VOLTAGE (V)
4.5
5.0
08084-121
0
2.5
GAIN = 6dB
RL = 4Ω + 15µH
POUT FOR BOTH CHANNELS
10
Figure 23. Maximum Output Power vs. Supply Voltage, RL = 4 Ω, AV = 6 dB
Rev. 0 | Page 9 of 16
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
OUTPUT POWER (W)
Figure 26. Efficiency vs. Output Power into 4 Ω
5.5
6.0
08084-124
0.5
SSM2356
0.8
0
GAIN = 6dB
RL = 8Ω + 33µH
0.7 I , P
SY OUT FOR BOTH CHANNELS
VDD = 5V
–10
–20
–30
VDD = 3.6V
0.5
CMRR (dB)
SUPPLY CURRENT (A)
0.6
0.4
VDD = 2.5V
0.3
–40
–50
–60
–70
0.2
–80
0.1
0.5
1.0
1.5
2.0
2.5
3.0
3.5
OUTPUT POWER (W)
08084-125
0
–100
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 27. Supply Current vs. Output Power into 8 Ω
08084-129
–90
0
Figure 30. CMRR vs. Frequency
1.6
0
GAIN = 6dB
RL = 4Ω + 15µH
1.4 I , P
SY OUT FOR BOTH CHANNELS
VDD = 5V
–10
–20
–30
VDD = 3.6V
1.0
PSRR (dB)
SUPPLY CURRENT (A)
1.2
0.8
VDD = 2.5V
0.6
–40
–50
–60
–70
0.4
–80
0.2
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5
OUTPUT POWER (W)
–100
10
08084-126
0
100
Figure 28. Supply Current vs. Output Power into 4 Ω
0
100k
6
5
SD INPUT
4
VOLTAGE (V)
–40
–60
RIGHT TO LEFT
–80
3
2
OUTPUT
1
0
–100
–120
1
10
100
1k
FREQUENCY (Hz)
10k
100k
Figure 29. Crosstalk v. Frequency
–2
–2
0
2
4
6
8
10
12
TIME (ms)
Figure 32. Turn-On Response
Rev. 0 | Page 10 of 16
14
16
18
08084-131
–1
LEFT TO RIGHT
08084-133
CHANNEL SEPARATION (dB)
10k
Figure 31. PSRR vs. Frequency
VDD = 5V
VOUT = 500mV rms
RL = 8Ω + 33µH
–20
1k
FREQUENCY (Hz)
08084-130
–90
SSM2356
7
6
5
OUTPUT
3
2
1
0
–1
–2
–110
SD INPUT
–90
–70
–50
–30
–10
10
TIME (µs)
30
50
70
08084-132
VOLTAGE (V)
4
Figure 33. Turn-Off Response
Rev. 0 | Page 11 of 16
SSM2356
TYPICAL APPLICATION CIRCUITS
VBATT
2.5V TO 5.5V
10µF
0.1µF
VDD
SSM2356
RIGHT AUDIO IN+
RIGHT AUDIO IN–
22nF R
EXT
SHUTDOWN–R
LEFT AUDIO IN–
INR– 80kΩ
22nF R
EXT
FET
DRIVER
INTERNAL
OSCILLATOR
OUTR–
EDGE
EDGE
CONTROL
BIAS
SDNL
80kΩ
GAIN
CONTROL
INL+
22nF REXT
OUTR+
MODULATOR
(Σ-Δ)
BIAS
SDNR
SHUTDOWN–L
LEFT AUDIO IN+
GAIN
CONTROL
INR+
22nF REXT
VDD
80kΩ
INL– 80kΩ
OUTL+
MODULATOR
(Σ-Δ)
FET
DRIVER
GND
GAIN
OUTL–
GND
08084-003
GAIN
EXTERNAL GAIN SETTINGS = 160kΩ/(80kΩ + R EXT ) {GAIN = GND}
= 640kΩ/(80kΩ + R EXT ) {GAIN = VBATT}
Figure 34. Stereo Differential Input Configuration
VBATT
2.5V TO 5.5V
10µF
0.1µF
VDD
SSM2356
SHUTDOWN–R
GAIN
CONTROL
INR– 80kΩ
22nF R
EXT
FET
DRIVER
INTERNAL
OSCILLATOR
OUTR–
EDGE
CONTROL
EDGE
BIAS
SDNL
80kΩ
GAIN
CONTROL
INL+
22nF REXT
OUTR+
MODULATOR
(Σ-Δ)
BIAS
SDNR
SHUTDOWN–L
LEFT AUDIO IN+
80kΩ
INR+
22nF REXT
VDD
INL– 80kΩ
OUTL+
MODULATOR
(Σ-Δ)
GAIN
FET
DRIVER
GND
OUTL–
GND
GAIN
EXTERNAL GAIN SETTINGS = 160kΩ/(80kΩ + R EXT ) {GAIN = GND}
= 640kΩ/(80kΩ + R EXT ) {GAIN = VBATT}
Figure 35. Stereo Single-Ended Input Configuration
Rev. 0 | Page 12 of 16
08084-004
RIGHT AUDIO IN+
22nF R
EXT
SSM2356
APPLICATIONS INFORMATION
OVERVIEW
The SSM2356 stereo Class-D audio amplifier features a filterless
modulation scheme that greatly reduces the external component
count, conserving board space and, thus, reducing systems cost.
The SSM2356 does not require an output filter but, instead,
relies on the inherent inductance of the speaker coil and the
natural filtering of the speaker and human ear to fully recover
the audio component of the square wave output. Most Class-D
amplifiers use some variation of pulse-width modulation
(PWM), but the SSM2356 uses Σ-Δ modulation to determine
the switching pattern of the output devices, resulting in a number
of important benefits. Σ-Δ modulators do not produce a sharp
peak with many harmonics in the AM frequency band, as pulsewidth modulators often do. Σ-Δ modulation provides the
benefits of reducing the amplitude of spectral components at
high frequencies, that is, reducing EMI emission that might
otherwise be radiated by speakers and long cable traces. Due to
the inherent spread-spectrum nature of Σ-Δ modulation, the
need for oscillator synchronization is eliminated for designs
incorporating multiple SSM2356 amplifiers.
•
•
•
•
System power-up/power-down
Mute/unmute
Input source change
Sample rate change
The SSM2356 has a pop-and-click suppression architecture that
reduces these output transients, resulting in noiseless activation and
deactivation.
EMI NOISE
The SSM2356 uses a proprietary modulation and spreadspectrum technology to minimize EMI emissions from the
device. For applications having difficulty passing FCC Class B
emission tests, the SSM2356 includes a modulation select pin
(ultralow EMI emission mode) that significantly reduces the
radiated emissions at the Class-D outputs, particularly above
100 MHz. Figure 36 shows SSM2356 EMI emission tests performed in a certified FCC Class-B laboratory in normal
emissions mode (EDGE = GND). Figure 37 shows SSM2356
EMI emission with EDGE = VDD, placing the device in low
emissions mode.
60
The SSM2356 also integrates overcurrent and temperature
protection.
50
GAIN SELECTION
40
(dBµV)
30
20
[1] HORIZONTAL
[2] VERTICAL
FCC CLASS-B LIMIT
10
It is possible to adjust the SSM2356 gain by using external
resistors at the input. To set a gain lower than 18 dB (or 6 dB
when GAIN = VDD), refer to Figure 34 for the differential input
configuration and Figure 35 for the single-ended configuration.
Calculate the external gain configuration as follows:
0
30
130
230
330
430
530
630
730
830
930 1000
FREQUENCY (MHz)
08084-005
The preset gain of SSM2356 can be selected between 6 dB and
18 dB with no external components and no change to the input
impedance. A major benefit of fixed input impedance is that
there is no need to recalculate input corner frequency (Fc)
when gain is adjusted. The same input coupling components
can be used for both gain settings.
Figure 36. EMI Emissions from SSM2356, 1-Channel, 12 cm Cable,
EDGE = GND
When GAIN = GND
60
External Gain Settings = 160 kΩ/(80 kΩ + REXT)
50
When GAIN = VDD
External Gain Settings = 640 kΩ/(80 kΩ + REXT)
Voltage transients at the output of audio amplifiers may occur
when shutdown is activated or deactivated. Voltage transients
as low as 10 mV can be heard as an audio pop in the speaker.
Clicks and pops can also be classified as undesirable audible
transients generated by the amplifier system and, therefore, as
not coming from the system input signal.
Such transients may be generated when the amplifier system
changes its operating mode. For example, the following can be
sources of audible transients:
Rev. 0 | Page 13 of 16
30
20
10
0
30
[1] HORIZONTAL
[2] VERTICAL
FCC CLASS-B LIMIT
130
230
330
430
530
630
730
830
930 1000
FREQUENCY (MHz)
Figure 37. EMI Emissions from SSM2356, 1-Channel, 12 cm Cable,
EDGE = VDD
08084-006
POP-AND-CLICK SUPPRESSION
(dBµV)
40
SSM2356
affecting efficiency. Use large traces for the power supply inputs
and amplifier outputs to minimize losses due to parasitic trace
resistance. Proper grounding guidelines help to improve audio
performance, minimize crosstalk between channels, and prevent
switching noise from coupling into the audio signal.
The measurements for Figure 36 and Figure 37 were taken in
an FCC-certified EMI laboratory with a 1 kHz input signal,
producing 0.5 W output power into an 8 Ω load from a 5 V
supply. Cable length was 12 cm, unshielded twisted pair
speaker cable. Note that reducing the supply voltage greatly
reduces radiated emissions.
OUTPUT MODULATION DESCRIPTION
The SSM2356 uses three-level, Σ-Δ output modulation. Each
output can swing from GND to VDD and vice versa. Ideally, when
no input signal is present, the output differential voltage is 0 V
because there is no need to generate a pulse. In a real-world
situation, there are always noise sources present.
Due to this constant presence of noise, a differential pulse is
generated, when required, in response to this stimulus. A small
amount of current flows into the inductive load when the differential pulse is generated. However, most of the time, output
differential voltage is 0 V, due to the Analog Devices three-level,
Σ-Δ output modulation. This feature ensures that the current
flowing through the inductive load is small.
When the user wants to send an input signal, an output pulse is
generated to follow input voltage. The differential pulse density
is increased by raising the input signal level. Figure 38 depicts
three-level, Σ-Δ output modulation with and without input
stimulus.
OUTPUT = 0V
OUT+
+5V
0V
–5V
OUTPUT > 0V
OUT+
+5V
0V
+5V
OUT–
0V
+5V
VOUT
If the system has separate analog and digital ground and power
planes, the analog ground plane should be directly beneath the
analog power plane, and, similarly, the digital ground plane should
be directly beneath the digital power plane. There should be no
overlap between analog and digital ground planes or between
analog and digital power planes.
The SSM2356 does not require input coupling capacitors if the
input signal is biased from 1.0 V to VDD − 1.0 V. Input capacitors
are required if the input signal is not biased within this recommended input dc common-mode voltage range, if high-pass
filtering is needed, or if a single-ended source is used. If highpass filtering is needed at the input, the input capacitor and the
input resistor of the SSM2356 form a high-pass filter whose
corner frequency is determined by the following equation:
0V
+5V
VOUT
Properly designed multilayer PCBs can reduce EMI emission
and increase immunity to the RF field by a factor of 10 or more,
compared with double-sided boards. A multilayer board allows
a complete layer to be used for the ground plane, whereas the
ground plane side of a double-sided board is often disrupted by
signal crossover.
INPUT CAPACITOR SELECTION
0V
+5V
OUT–
To maintain high output swing and high peak output power, the
PCB traces that connect the output pins to the load and supply
pins should be as wide as possible to maintain the minimum
trace resistances. It is also recommended that a large ground
plane be used for minimum impedances. In addition, good PCB
layout isolates critical analog paths from sources of high interference. High frequency circuits (analog and digital) should be
separated from low frequency circuits.
fC = 1/(2π × RIN × CIN)
0V
OUTPUT < 0V
OUT+
The input capacitor can significantly affect the performance of
the circuit. Not using input capacitors degrades both the output
offset of the amplifier and the dc PSRR performance.
+5V
0V
+5V
OUT–
0V
VOUT
–5V
08084-007
0V
Figure 38. Three-Level, Σ-Δ Output Modulation With and
Without Input Stimulus
LAYOUT
As output power continues to increase, care must be taken to
lay out PCB traces and wires properly among the amplifier,
load, and power supply. A good practice is to use short, wide
PCB tracks to decrease voltage drops and minimize inductance.
Ensure that track widths are at least 200 mil for every inch of
track length for the lowest dc resistance (DCR), and use 1 oz. or
2 oz. copper PCB traces to further reduce IR drops and
inductance. A poor layout increases voltage drops, consequently
PROPER POWER SUPPLY DECOUPLING
To ensure high efficiency, low total harmonic distortion (THD),
and high PSRR, proper power supply decoupling is necessary.
Noise transients on the power supply lines are short-duration
voltage spikes. These spikes can contain frequency components
that extend into the hundreds of megahertz. The power supply
input must be decoupled with a good quality, low ESL, low ESR
capacitor, greater than 4.7 μF. This capacitor bypasses low frequency noises to the ground plane. For high frequency transient
noises, use a 0.1 μF capacitor as close as possible to the VDD
pin of the device. Placing the decoupling capacitor as close as
possible to the SSM2356 helps to maintain efficient
performance.
Rev. 0 | Page 14 of 16
SSM2356
OUTLINE DIMENSIONS
0.660
0.600
0.540
1.700
1.660 SQ
1.620
SEATING
PLANE
4
3
2
1
A
BALL A1
IDENTIFIER
0.290
0.260
0.230
1.20
BSC
B
C
D
0.40
BSC
0.430
0.400
0.370
0.07
COPLANARITY
BOTTOM VIEW
(BALL SIDE UP)
0.230
0.200
0.170
040209-B
TOP VIEW
(BALL SIDE DOWN)
Figure 4. 16-Ball Wafer Level Chip Scale Package [WLCSP]
(CB-16-4)
Dimensions shown in millimeters
ORDERING GUIDE
Model
SSM2356CBZ-REEL1
SSM2356CBZ-REEL71
EVAL-SSM2356Z1
1
Temperature Range
−40°C to +85°C
−40°C to +85°C
Package Description
16-Ball Wafer Level Chip Scale Package [WLCSP]
16-Ball Wafer Level Chip Scale Package [WLCSP]
Evaluation Board
Z = RoHS Compliant Part.
Rev. 0 | Page 15 of 16
Package Option
CB-16-4
CB-16-4
Branding
Y1R
Y1R
SSM2356
NOTES
©2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08084-0-5/09(0)
Rev. 0 | Page 16 of 16