2 × 2W Filterless Class-D
Stereo Audio Amplifier
SSM2356
Data Sheet
FEATURES
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.
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 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
TE
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.
LE
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
B
SO
GENERAL DESCRIPTION
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.
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 100
V
V
ms
µs
kΩ
29
µVrms
100
dB
B
SO
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
O
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
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
VDD
PSRR
(DC)
PSRRGSM
ISY
GAIN CONTROL
Closed-Loop Gain
1
Typ
TE
Efficiency
Symbol
LE
Parameter
DEVICE CHARACTERISTICS
Output Power/Channel
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. A | Page 3 of 16
SSM2356
Data Sheet
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.
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
O
B
SO
LE
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. A | Page 4 of 16
θJA
66
θJB
19
TE
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)
Unit
°C/W
Data Sheet
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+
TE
TOP VIEW
(BALL SIDE DOWN)
Not to Scale
08084-002
D
Figure 2. Pin Configuration (Top Side View)
Table 4. Pin Function Descriptions
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.
OUTR+
GND
VDD
VDD
EDGE
Noninverting Output for Right Channel.
Ground.
Power Supply.
Power Supply.
Edge Control (Low Emission Mode); active high digital input.
B
SO
O
A4
B3
A2
A3
C2
LE
Bump
A1
B1
C1
Rev. A | Page 5 of 16
SSM2356
Data Sheet
TYPICAL PERFORMANCE CHARACTERISTICS
100
100
RL = 8Ω + 33µH
GAIN = 6dB
VDD = 2.5V
VDD = 2.5V
10
THD + N (%)
10
THD + N (%)
RL = 4Ω + 15µH
GAIN = 18dB
VDD = 3.6V
1
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
1
10
10
VDD = 5V
GAIN = 6dB
RL = 8Ω + 33µH
LE
10
0.1
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
TE
VDD = 5V
THD + N (%)
THD + N (%)
1
1
0.1
1W
0.1
0.25W
B
SO
0.01
VDD = 5V
0.001
0.01
0.1
1
10
OUTPUT POWER (W)
0.5W
0.0001
10
VDD = 3.6V
0.1
100k
VDD = 5V
GAIN = 18dB
RL = 8Ω + 33µH
10
THD + N (%)
O
0.01
1
1W
0.1
0.01
0.5W
0.25W
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
1k
10k
100k
FREQUENCY (Hz)
Figure 8. THD + N vs. Frequency, VDD = 5 V, RL = 8 Ω, AV = 18 dB
Rev. A | Page 6 of 16
08084-106
VDD = 5V
08084-103
THD + N (%)
100
VDD = 2.5V
1
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
08084-105
0.001
0.0001
0.001
08084-102
0.01
Data Sheet
100
SSM2356
100
VDD = 5V
GAIN = 6dB
RL = 4Ω + 15µH
10
THD + N (%)
THD + N (%)
10
VDD = 3.6V
GAIN = 18dB
RL = 8Ω + 33µH
1
2W
0.1
0.01
1
0.5W
0.1
0.01
0.5W
0.125W
0.25W
1k
10k
100k
FREQUENCY (Hz)
Figure 9. THD + N vs. Frequency, VDD = 5 V, RL = 4 Ω, AV = 6 dB
100
100
1k
10k
100k
FREQUENCY (Hz)
Figure 12. THD + N vs. Frequency, VDD = 3.6 V, RL = 8 Ω, AV = 18 dB
100
VDD = 5V
GAIN = 18dB
RL = 4Ω + 15µH
10
VDD = 3.6V
GAIN = 6dB
RL = 4Ω + 15µH
10
THD + N (%)
LE
THD + N (%)
0.001
10
08084-110
100
TE
0.001
10
08084-107
1W
1
2W
0.5W
0.1
1
1W
0.1
0.25W
0.01
0.01
1k
10k
100k
FREQUENCY (Hz)
0.5W
0.001
10
100
0.1
0.5W
VDD = 3.6V
GAIN = 18dB
RL = 4Ω + 15µH
1
1W
0.1
0.25W
0.125W
0.01
100k
10
THD + N (%)
O
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. A | Page 7 of 16
08084-112
0.25W
08084-109
THD + N (%)
1
10k
Figure 13. THD + N vs. Frequency, VDD = 3.6 V, RL = 4 Ω, AV = 6 dB
VDD = 3.6V
GAIN = 6dB
RL = 8Ω + 33µH
10
1k
FREQUENCY (Hz)
Figure 10. THD + N vs. Frequency, VDD = 5 V, RL = 8 Ω, AV = 18 dB
100
100
08084-111
100
08084-108
0.001
10
B
SO
1W
SSM2356
100
Data Sheet
100
VDD = 2.5V
GAIN = 6dB
RL = 8Ω + 33µH
10
THD + N (%)
THD + N (%)
10
VDD = 2.5V
GAIN = 18dB
RL = 4Ω + 15µH
1
0.25W
0.1
0.5W
1
0.1
1.25W
0.0625W
0.01
0.01
0.25W
1k
10k
100k
FREQUENCY (Hz)
0.001
10
7.0
6.0
5.5
8Ω + 33µH
5.0
4.5
B
SO
0.125W
100
1k
10k
100k
FREQUENCY (Hz)
4.0
2.5
7.5
0.1
0.25W
4.0
4.5
5.0
5.5
ISY FOR BOTH CHANNELS
GAIN = 18dB
7.0
SUPPLY CURRENT (mA)
O
1
3.5
Figure 19. Supply Current vs. Supply Voltage, AV = 6 dB
VDD = 2.5V
GAIN = 6dB
RL = 4Ω + 15µH
0.5W
3.0
NO LOAD
SUPPLY VOLTAGE (V)
Figure 16. THD + N vs. Frequency, VDD = 2.5 V, RL = 8 Ω, AV = 18 dB
10
4Ω + 15µH
08084-117
SUPPLY CURRENT (mA)
0.0625W
0.01
6.5
4Ω + 15µH
6.0
8Ω + 33µH
5.5
5.0
NO LOAD
0.01
4.5
100
1k
10k
100k
FREQUENCY (Hz)
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. A | Page 8 of 16
5.5
08084-118
0.125W
0.001
10
08084-115
THD + N (%)
ISY FOR BOTH CHANNELS
GAIN = 6dB
LE
0.25W
08084-114
THD + N (%)
1
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
TE
100
08084-113
0.001
10
08084-116
0.125W
Data Sheet
SSM2356
3.5
2.0
f = 1kHz
GAIN = 18dB
3.0 RL = 4Ω + 15µH
f = 1kHz
1.8 GAIN = 6dB
RL = 8Ω + 33µH
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
0.5
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
Figure 21. Maximum Output Power vs. Supply Voltage, RL = 8 Ω, AV = 6 dB
1.8
EFFICIENCY (%)
1%
0.6
60
50
40
3.5
4.0
4.5
5.0
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
Figure 25. Efficiency vs. Output Power into 8 Ω
100
f = 1kHz
GAIN = 6dB
3.0 RL = 4Ω + 15µH
1.5
1%
80
70
EFFICIENCY (%)
O
10%
90
VDD = 2.5V
VDD = 5V
VDD = 3.6V
60
50
40
30
1.0
20
0.5
GAIN = 6dB
RL = 4Ω + 15µH
POUT FOR BOTH CHANNELS
3.0
3.5
4.0
SUPPLY VOLTAGE (V)
4.5
5.0
08084-121
10
Figure 23. Maximum Output Power vs. Supply Voltage, RL = 4 Ω, AV = 6 dB
Rev. A | 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
3.0
GAIN = 6dB
RL = 8Ω + 33µH
POUT FOR BOTH CHANNELS
10
08084-123
B
SO
20
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
VDD = 5V
VDD = 3.6V
30
0.4
0
2.5
5.0
VDD = 2.5V
LE
0.8
08084-120
OUTPUT POWER (W)
1.0
2.0
4.5
70
10%
2.5
4.0
Figure 24. Maximum Output Power vs. Supply Voltage, RL = 4 Ω, AV = 18 dB
80
1.2
3.5
3.5
90
1.4
0
2.5
3.0
SUPPLY VOLTAGE (V)
100
f = 1kHz
GAIN = 18dB
1.6
RL = 8Ω + 33µH
0.2
0
2.5
08084-122
3.0
TE
0
2.5
08084-119
0.2
SSM2356
Data Sheet
0
0.8
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)
–100
10
100
1k
10k
100k
TE
0
08084-125
0
FREQUENCY (Hz)
Figure 27. Supply Current vs. Output Power into 8 Ω
08084-129
–90
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
LE
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
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
100
Figure 28. Supply Current vs. Output Power into 4 Ω
0
RIGHT TO LEFT
100k
6
5
SD INPUT
4
VOLTAGE (V)
–60
O
3
2
OUTPUT
1
–80
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. A | Page 10 of 16
14
16
18
08084-131
–1
LEFT TO RIGHT
08084-133
CHANNEL SEPARATION (dB)
–40
10k
Figure 31. PSRR vs. Frequency
VDD = 5V
VOUT = 500mV rms
RL = 8Ω + 33µH
–20
1k
FREQUENCY (Hz)
08084-130
0
–90
08084-126
0
B
SO
–80
0.2
Data Sheet
SSM2356
7
6
5
VOLTAGE (V)
4
OUTPUT
3
2
1
0
–1
–90
–70
–50
–30
–10
10
TIME (µs)
30
50
70
O
B
SO
LE
Figure 33. Turn-Off Response
TE
SD INPUT
08084-132
–2
–110
Rev. A | Page 11 of 16
SSM2356
Data Sheet
TYPICAL APPLICATION CIRCUITS
VBATT
2.5V TO 5.5V
10µF
0.1µF
VDD
SSM2356
22nF REXT
SDNR
FET
DRIVER
OUTR–
EDGE
EDGE
CONTROL
INTERNAL
OSCILLATOR
BIAS
SHUTDOWN–L
LEFT AUDIO IN–
INR– 80kΩ
MODULATOR
(Σ-Δ)
BIAS
SHUTDOWN–R
LEFT AUDIO IN+
OUTR+
GAIN
CONTROL
INR+
22nF R
EXT
SDNL
80kΩ
22nF REXT
OUTL+
GAIN
CONTROL
INL+
INL– 80kΩ
MODULATOR
(Σ-Δ)
FET
DRIVER
OUTL–
GAIN
GND
GAIN
GND
08084-003
RIGHT AUDIO IN–
VDD
80kΩ
TE
RIGHT AUDIO IN+
22nF R
EXT
EXTERNAL GAIN SETTINGS = 160kΩ/(80kΩ + R EXT) {GAIN = GND}
= 640kΩ/(80kΩ + R EXT) {GAIN = VBATT}
LE
Figure 34. Stereo Differential Input Configuration
(When GAIN = VBATT use no larger than 10 kΩ REXT)
VBATT
2.5V TO 5.5V
10µF
0.1µF
VDD
SSM2356
RIGHT AUDIO IN+
22nF R
EXT
80kΩ
INR+
GAIN
CONTROL
INR– 80kΩ
MODULATOR
(Σ-Δ)
B
SO
22nF REXT
FET
DRIVER
OUTR+
OUTR–
BIAS
SHUTDOWN–R
SDNR
INTERNAL
OSCILLATOR
EDGE
CONTROL
EDGE
BIAS
SHUTDOWN–L
LEFT AUDIO IN+
VDD
22nF R
EXT
SDNL
80kΩ
GAIN
CONTROL
INL+
22nF REXT
INL– 80kΩ
OUTL+
MODULATOR
(Σ-Δ)
GAIN
FET
DRIVER
GND
OUTL–
GND
O
EXTERNAL GAIN SETTINGS = 160kΩ/(80kΩ + R EXT) {GAIN = GND}
= 640kΩ/(80kΩ + R EXT) {GAIN = VBATT}
Figure 35. Stereo Single-Ended Input Configuration
(When GAIN = VBATT use no larger than 10 kΩ REXT)
Rev. A | Page 12 of 16
08084-004
GAIN
Data Sheet
SSM2356
APPLICATIONS INFORMATION
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.
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 = GND), refer to Figure 34 for the differential input
configuration and Figure 35 for the single-ended configuration.
Calculate the external gain configuration as follows:
When GAIN = GND (6 dB default gain setting)
O
External Gain Settings = 160 kΩ/(80 kΩ + REXT)
60
50
40
30
20
[1] HORIZONTAL
[2] VERTICAL
FCC CLASS-B LIMIT
10
0
30
130
230
330
430
530
630
730
830
930 1000
FREQUENCY (MHz)
08084-005
B
SO
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.
(dBµV)
The SSM2356 also integrates overcurrent and temperature
protection.
Figure 36. EMI Emissions from SSM2356, 1-Channel, 12 cm Cable,
EDGE = GND
When GAIN = VDD (18 dB default gain setting)
60
External Gain Settings = 640 kΩ/(80 kΩ + REXT)
50
POP-AND-CLICK SUPPRESSION
40
(dBµV)
Please note that when using external resistors to adjust the gain
from the 18 dB setting (GAIN = VDD) to maintain optimal audio
performance, it is not recommended to use external series resistors
larger than 10 kΩ due to increased noise floor and reduced
THD+N performance.
30
20
10
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.
Rev. A | Page 13 of 16
0
30
[1] HORIZONTAL
[2] VERTICAL
FCC CLASS-B LIMIT
130
230
330
430
530
630
FREQUENCY (MHz)
730
830
930 1000
08084-006
GAIN SELECTION
•
•
•
•
LE
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 pulse-width 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.
Such transients may be generated when the amplifier system
changes its operating mode. For example, the following can be
sources of audible transients:
TE
OVERVIEW
Figure 37. EMI Emissions from SSM2356, 1-Channel, 12 cm Cable,
EDGE = VDD
SSM2356
Data Sheet
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.
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.
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
+5V
INPUT CAPACITOR SELECTION
0V
+5V
OUT–
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
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.
B
SO
OUT+
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.
LE
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.
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.
TE
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.
0V
O
OUT+
OUT–
VOUT
0V
+5V
0V
0V
–5V
fC = 1/(2π × RIN × CIN)
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
08084-007
OUTPUT < 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. A | Page 14 of 16
Data Sheet
SSM2356
OUTLINE DIMENSIONS
1.700
1.660 SQ
1.620
4
3
2
1
A
BALL A1
IDENTIFIER
B
1.20
REF
C
D
0.40
BSC
(BALL SIDE UP)
SIDE VIEW
0.430
0.400
0.370
TE
COPLANARITY
0.07
0.290
0.260
0.230
0.230
0.200
0.170
10-19-2012-B
SEATING
PLANE
BOTTOM VIEW
LE
0.660
0.600
0.540
TOP VIEW
(BALL SIDE DOWN)
Figure 4. 16-Ball Wafer Level Chip Scale Package [WLCSP]
(CB-16-4)
Dimensions shown in millimeters
ORDERING GUIDE
Package Description
16-Ball Wafer Level Chip Scale Package [WLCSP]
16-Ball Wafer Level Chip Scale Package [WLCSP]
Evaluation Board
Z = RoHS Compliant Part.
O
1
Temperature Range
−40°C to +85°C
−40°C to +85°C
B
SO
Model 1
SSM2356CBZ-RL
SSM2356CBZ-RL7
EVAL-SSM2356Z
Rev. A | Page 15 of 16
Package Option
CB-16-4
CB-16-4
Branding
Y1R
Y1R
SSM2356
Data Sheet
O
B
SO
LE
TE
NOTES
©2009–2013 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08084-0-3/13(A)
Rev. A | Page 16 of 16
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