Dual Single-Supply
Audio Operational Amplifier
SSM2135
Rev. G
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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
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Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2003–2011 Analog Devices, Inc. All rights reserved.
FEATURES
Excellent sonic characteristics
High output drive capability
5.2 nV/√Hz equivalent input noise @ 1 kHz
0.003% THD + N (VOUT = 1 V p-p @ 1 kHz)
3.5 MHz gain bandwidth
Unity-gain stable
Low cost
APPLICATIONS
Multimedia audio systems
Microphone preamplifiers
Headphone drivers
Differential line receivers
Balanced line drivers
Audio ADC input buffers
Audio DAC l-V converters and filters
Pseudoground generators
PIN CONNECTIONS
OUT A 1
–IN A 2
+IN A 3
V
–/GND 4
V+
8
OUT B
7
–IN B6
+IN B5
SSM2135
TO P VIE W
(Not to Scale)
00349-002
Figure 1. 8-Lead Narrow Body SOIC (R Suffix)
GENERAL DESCRIPTION
The SSM2135 dual audio operational amplifier permits excel-
lent performance in portable or low power audio systems, with
an operating supply range of 4 V to 36 V or ±2 V to ±18 V.
The unity-gain stable device has very low voltage noise of
5.2 nV/√Hz, and total harmonic distortion plus noise below
0.01% over normal signal levels and loads. Such characteristics
are enhanced by wide output swing and load drive capability.
A unique output stage permits output swing approaching the
rail under moderate load conditions. Under severe loading,
the SSM2135 still maintains a wide output swing with ultralow
distortion. Particularly well suited for computer audio systems
and portable digital audio units, the SSM2135 can perform
preamplification, headphone and speaker driving, and balanced
line driving and receiving. Additionally, the device is ideal for
input signal conditioning in single-supply, Σ-Δ, analog-to-
digital converter subsystems such as the AD1877. The SSM2135
makes an ideal single-supply stereo output amplifier for audio
digital-to-analog converters (DACs) because of its low noise
and distortion.
The SSM2135 is available in an 8-lead plastic SOIC package
and is guaranteed for operation over the extended industrial
temperature range of −40°C to +85°C.
FUNCTIONAL BLOCK DIAGRAM
+INx 9V
INx 9V
V
+
V–/GND
OUTx
00349-001
Figure 2.
SSM2135
Rev. G | Page 2 of 16
TABLE OF CONTENTS
Features.............................................................................................. 1
Applications....................................................................................... 1
Pin Connections ............................................................................... 1
General Description......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 4
Thermal Resistance.......................................................................4
ESD Caution...................................................................................4
Typical Performance Characteristics ..............................................5
Applications Information.............................................................. 10
Application Circuits................................................................... 10
Outline Dimensions....................................................................... 14
Ordering Guide .......................................................................... 14
REVISION HISTORY
4/11—Rev. F to Rev. G
Changes to Figure 36...................................................................... 12
2/09—Rev. E to Rev. F
Updated Format..................................................................Universal
Changes to Features Section, General Description Section, and
Figure 1 Caption ............................................................................... 1
Changes to Specifications Section Conditions ............................. 3
Changed AVO Symbol to AV............................................................. 3
Changes to Supply Current Parameter, Table 1 ............................ 3
Deleted ESD Ratings Table.............................................................. 3
Changes to Figure 4 and Figure 5................................................... 5
Changes to Figure 9.......................................................................... 6
Changes to Figure 15, Figure 13, and Figure 18 ........................... 7
Changes to Figure 21, Figure 24 Caption, and Figure 25............ 8
Changes to Figure 27 and Figure 28............................................... 9
Deleted Figure 5; Renumbered Sequentially............................... 10
Deleted 18-Bit Stereo CD-DAC Output Amplifier Section...... 10
Changes to Applications Information Section, Low Noise Stereo
Headphone Driver Amplifier Section, Figure 31, and Figure 32
........................................................................................................... 10
Changes to Low Noise Microphone Preamplifier Section,
Figure 33, and Figure 34................................................................ 11
Changes to Figure 37...................................................................... 12
Deleted Spice Macromodel Section ............................................. 12
Changes to Digital Volume Control Circuit Section, Figure 38,
and Figure 39................................................................................... 13
Updated Outline Dimensions....................................................... 14
Changes to Ordering Guide.......................................................... 14
2/03—Rev. D to Rev. E
Removed 8-Lead Plastic DIP Package.............................Universal
Edits to Thermal Characteristics.....................................................4
Edits to Outline Dimensions......................................................... 14
Updated Ordering Guide .............................................................. 14
SSM2135
Rev. G | Page 3 of 16
SPECIFICATIONS
VS = 5 V, −40°C ≤ TA ≤ +85°C, unless otherwise noted. Typical specifications apply at TA = 25°C.
Table 1.
Parameter Symbol Conditions Min Typ Max Unit
AUDIO PERFORMANCE
Voltage Noise Density en f = 1 kHz 5.2 nV/√Hz
Current Noise Density in f = 1 kHz 0.5 pA/√Hz
Signal-To-Noise Ratio SNR 20 Hz to 20 kHz, 0 dBu = 0.775 V rms 121 dBu
Headroom HR Clip point = 1% THD + N, f = 1 kHz, RL = 10 kΩ 5.3 dBu
Total Harmonic Distortion Plus Noise THD + N AV = +1, VOUT = 1 V p-p, f = 1 kHz, 80 kHz LPF
R
L = 10 kΩ 0.003 %
R
L = 32 Ω 0.005 %
DYNAMIC PERFORMANCE
Slew Rate SR RL = 2 kΩ, TA = 25°C 0.6 0.9 V/μs
Gain Bandwidth Product GBW 3.5 MHz
Settling Time tS To 0.1%, 2 V Step 5.8 μs
INPUT CHARACTERISTICS
Input Voltage Range VCM 0 4.0 V
Input Offset Voltage VOS VOUT = 2 V 0.2 2.0 mV
Input Bias Current IB VCM = 0 V, VOUT = 2 V 300 750 nA
Input Offset Current IOS VCM = 0 V, VOUT = 2 V 50 nA
Differential Input Impedance ZIN 4
Common-Mode Rejection CMR 0 V ≤ VCM ≤ 4 V, f = dc 87 112 dB
Large Signal Voltage Gain AV 0.01 V ≤ VOUT ≤ 3.9 V, RL = 600 Ω 2 V/μV
OUTPUT CHARACTERISTICS
Output Voltage Swing High VOH RL = 100 kΩ 4.1 V
R
L = 600 Ω 3.9 V
Output Voltage Swing Low VOL RL = 100 kΩ 3.5 mV
R
L = 600 Ω 3.0 mV
Short-Circuit Current Limit ISC ±30 mA
POWER SUPPLY
Supply Voltage Range VS Single supply 4 36 V
Dual supply ±2 ±18 V
Power Supply Rejection Ratio PSRR VS = 4 V to 6 V, f = dc 90 120 dB
Supply Current ISY V
S = 5 V, VOUT = 2.0 V, no load 2.8 6.0 mA
V
S = ±18 V, VOUT = 0 V, no load 3.7 7.6 mA
SSM2135
Rev. G | Page 4 of 16
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
Supply Voltage
Single Supply 36 V
Dual Supply ±18 V
Input Voltage ±VS
Differential Input Voltage 10 V
Output Short-Circuit Duration Indefinite
Storage Temperature Range −65°C to +150°C
Operating Temperature Range −40°C to +85°C
Junction Temperature Range (TJ) −65°C to +150°C
Lead Temperature (Soldering, 60 sec) 300°C
THERMAL RESISTANCE
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Table 3.
Package Type θJA θ
JC Unit
8-Lead SOIC (R-8) 158 43 °C/W
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.
SSM2135
Rev. G | Page 5 of 16
TYPICAL PERFORMANCE CHARACTERISTICS
5V
R
L
2.5V DC
500µF
00349-003
Figure 3. Test Circuit for Figure 4, Figure 5, and Figure 6
1
0.0005
0.001
0.01
0.1
50m 0.1 1 5
THD + N (%)
INPUT VOLTAGE (V p-p)
R
L
= 32
R
L
= 10k
A
V
= +1
V
S
= 5V
f = 1kHz
80kHz LOW-PASS FILTER
00349-004
Figure 4. THD + N vs. Amplitude (See Figure 3)
1
0.0005
0.001
0.01
0.1
20 100 1k 10k 20k
THD + N (%)
FREQUENCY (Hz)
AV = +1
VS = 5V
VIN = 1V p-p
80kHz LOW-PASS FILTER
RL = 32
RL = 10k
00349-005
Figure 5. THD + N vs. Frequency (See Figure 3)
10
1
0.001
0.01
0.1
10 100 1k 10k
THD + N (%)
LOAD RESISTANCE ()
VS = 5V
AV = +1
f = 1kHz
VIN = 1V p-p
RL = 10k
80kHz LOW-PASS FILTER
00349-006
Figure 6. THD + N vs. Load (See Figure 3)
1
0.1
0.001
0.01
0 102030405060
THD + N (%)
GAIN (dB)
V
S
= 5V
f = 1kHz
V
OUT
= 2.5V p-p
R
L
= 100k
80kHz LOW-PASS FILTER
NONINVERTING
INVERTING
00349-007
Figure 7. THD + N vs. Gain
1
0.1
0.001
0.01
0 5 10 15 20 25 30
THD + N (%)
SUPPLY VOLTAGE (V)
V
S
= 5V
A
V
= +1
f = 1kHz
V
IN
= 1V p-p
R
L
= 10k
80kHz LOW-PASS FILTER
00349-008
Figure 8. THD + N vs. Supply Voltage
SSM2135
Rev. G | Page 6 of 16
10
1
0.1
0.001
0.01
50m 0.1 1 5
SMPTE (%)
AMPLITUDE (V p-p)
V
S
= 5V
A
V
= +1
f = 1kHz
R
L
= 10k
00349-009
Figure 9. SMPTE Intermodulation Distortion
100
90
10
0%
1s
00349-010
Figure 10. Input Voltage Noise (20 nV/Div)
30
25
20
15
10
5
0
1 10 100 1k
e
n
(nV/ Hz)
FREQUENCY (Hz)
V
S
= 5V
T
A
= 25°C
00349-011
Figure 11. Voltage Noise Density vs. Frequency
5
4
3
2
1
0
1 10 100 1k
i
n
(pA/ Hz)
FREQUENCY (Hz)
V
S
= 5V
T
A
= 25°C
00349-012
Figure 12. Current Noise Density vs. Frequency
2.0
–2.0
–1.5
–1.0
–0.5
0
0.5
1.0
1.5
10 100 1k 10k 100k
AMPLITUDE (dBu)
FREQUENCY (Hz)
A
V
= +1
V
S
= 5V
V
IN
= 1V p-p
R
L
= 10k
00349-013
Figure 13. Frequency Response
100
90
10
0%
5µs5µs
20mV20mV
00349-014
Figure 14. Square Wave Response (VS = 5 V, AV = +1, RL = ∞)
SSM2135
Rev. G | Page 7 of 16
60
–140
–120
–100
–80
–60
–40
–20
0
20
40
10 100 1k 10k 100k 1M 10M
CROSSTALK (dB)
FREQUENCY (Hz)
V
S
= 5V
T
A
= 25°C
R
L
= 10k
–105
00349-015
Figure 15. Crosstalk vs. Frequency
140
120
100
80
60
40
20
0
100 1M100k10k1k
COMMON-MODE REJECTION (dB)
FREQUENCY (Hz)
V
S
= 5V
T
A
= 25°C
00349-016
Figure 16. Common-Mode Rejection vs. Frequency
140
120
100
80
60
40
20
0
–20
10 100 1M100k10k1k
PSRR (dB)
FREQUENCY (Hz)
V
S
= 5V
A
V
= +1
T
A
= 25°C
+PSRR
–PSRR
00349-017
Figure 17. Power Supply Rejection Ratio vs. Frequency
50
–20
–10
0
10
20
30
40
1k 10M1M100k10k
CLOSED-LOOP GAIN (dB)
FREQUENCY (Hz)
V
S
= 5V
T
A
= 25°C
A
V
= +100
A
V
= +10
A
V
= +1
00349-018
Figure 18. Closed-Loop Gain vs. Frequency
100
–20
0
20
40
60
80
225
180
135
90
45
0
1k 10M1M100k10k
OPEN-LOOP GAIN (dB)
PHASE (Degrees)
FREQUENCY (Hz)
V
S
= 5V
T
A
= 25°C
GAIN
PHASE
00349-019
Figure 19. Open-Loop Gain and Phase vs. Frequency
50
45
40
35
25
30
20
15
10
5
0
0 100 200 300 400 500
OVERSHOOT (%)
LOAD CAPACITANCE (pF)
V
S
= 5V
R
L
= 2k
V
IN
= 100mV p-p
T
A
= 25°C
A
V
= +1
NEGATIVE EDGE
POSITIVE EDGE
00349-020
Figure 20. Small Signal Overshoot vs. Load Capacitance
SSM2135
Rev. G | Page 8 of 16
50
45
40
35
25
30
20
15
10
5
0
10 100 1k 10k 100k 1M
IMPEDANCE
(
)
FREQUENCY (Hz)
V
S
= 5V
T
A
= 25°C
A
V
= +100
A
V
= +10
A
V
= +1
00349-021
Figure 21. Output Impedance vs. Frequency
5
4
3
2
1
0
1 10 100 1k 10k 100k
MAXIMUM OUTPUT (V)
LOAD RESISTANCE ()
V
S
= 5V
T
A
= 25°C
A
V
= +1
f = 1kHz
THD + N = 1%
00349-022
Figure 22. Maximum Output Voltage vs. Load Resistance
6
5
4
3
2
1
0
1k 10k 100k 1M 10M
MAXIMUM OUTPUT SWING (V)
FREQUENCY (Hz)
V
S
= 5V
R
L
= 2k
T
A
= 25°C
A
V
= +1
00349-023
Figure 23. Maximum Output Swing vs. Frequency
40
35
30
25
20
15
10
5
0
043530252015105
OUTPUT VOLTAGE (V)
SUPPLY VOLTAGE (V)
0
V
S
= 5V
A
V
= +1
R
L
= 10k
f = 1kHz
THD + N = 1%
T
A
= 25°C
00349-024
Figure 24. Output Voltage vs. Supply Voltage
5.0
3.0
3.5
4.0
4.5
2.0
0
0.5
1.0
1.5
–75 1251007550250–25–50
POSITIVE OUTPUT SWING (V)
NEGATIVE OUTPUT SWING (mV)
TEMPERATURE (°C)
V
S
= 5V
+SWING
R
L
= 2k
+SWING
R
L
= 600–SWING
R
L
= 2k
–SWING
R
L
= 600
00349-025
Figure 25. Output Swing vs. Temperature and Load
2.0
0
0.5
1.0
1.5
–75 1251007550250–25–50
SLEW RATE (V/µs)
TEMPERATURE (°C)
V
S
= 5V
0.5V V
OUT
4V
+SLEW RATE
–SLEW RATE
00349-026
Figure 26. Slew Rate vs. Temperature
SSM2135
Rev. G | Page 9 of 16
20
18
16
14
12
10
8
6
4
2
0
–75 1251007550250–25–50
OPEN-LOOP GAIN (V/µV)
TEMPERATURE (°C)
V
S
= 5V
V
OUT
= 3.9V
R
L
= 2k
R
L
= 600
00349-027
Figure 27. Open-Loop Gain vs. Temperature
70
50
55
60
65
5
1
2
3
4
–75 1251007550250–25–50
PHASE MARGIN (Degrees)
GAIN BANDWIDTH PRODUCT (MHz)
TEMPERATURE (°C)
V
S
= 5V
GBW
Φm
00349-028
Figure 28. Gain Bandwidth Product and Phase Margin vs. Temperature
5
4
3
2
1
0
–75 1251007550250–25–50
SUPPLY CURRENT (mA)
TEMPERATURE (°C)
V
S
= ±18V V
S
= ±15V
V
S
= +5V
00349-029
Figure 29. Supply Current vs. Temperature
500
400
300
200
100
0
–75 1251007550250–25–50
INPUT BIAS CURRENT (nA)
TEMPERATURE (°C)
V
S
= ±15V
V
S
= +5V
00349-030
Figure 30. Input Bias Current vs. Temperature
SSM2135
Rev. G | Page 10 of 16
APPLICATIONS INFORMATION
The SSM2135 is a low voltage audio amplifier that has exception-
ally low noise and excellent sonic quality even when driving loads
as small as 25 Ω. Designed for single supply use, the inputs and
output can both swing very close to 0 V. Thus with a supply
voltage at 5 V, both the input and output swing from 0 V to 4 V.
Because of this, signal dynamic range can be optimized if the
amplifier is biased to a 2 V reference rather than at half the
supply voltage.
The SSM2135 is unity-gain stable, even when driving into a fair
amount of capacitive load. Driving up to 500 pF does not cause
any instability in the amplifier. However, overshoot in the
frequency response increases slightly.
The SSM2135 makes an excellent output amplifier for 5 V only
audio systems such as a multimedia workstation, a CD output
amplifier, or an audio mixing system. The amplifier has large
output swing even at this supply voltage because it is designed
to swing to the negative rail. In addition, it easily drives load
impedances as low as 25 Ω with low distortion.
The SSM2135 is fully protected from phase reversal for inputs
going to the negative supply rail. However, internal ESD protec-
tion diodes turn on when either input is forced more than 0.5 V
below the negative rail. Under this condition, input current in
excess of 2 mA may cause erratic output behavior, in which case,
a current limiting resistor should be included in the offending
input if phase integrity is required with excessive input voltages.
A 500 Ω or higher series input resistor prevents phase inversion
even with the input pulled 1 V below the negative supply.
Hot plugging the input to a signal generally does not present a
problem for the SSM2135, assuming that the signal does not
have any voltage exceeding the supply voltage of the device.
If so, it is advisable to add a series input resistor to limit the
current, as well as a Zener diode to clamp the input to a voltage
no higher than the supply.
APPLICATION CIRCUITS
Low Noise Stereo Headphone Driver Amplifier
Figure 31 shows the SSM2135 used in a stereo headphone driver
for multimedia applications with the AD1845, a 16-bit stereo
codec. The SSM2135 is equally well suited for the serial-bused
AD1849 stereo codec. The impedance of the headphone can be
as low as 25 Ω, which covers most commercially available high
fidelity headphones. Although the amplifier can operate at up to
±18 V supply, it is just as efficient powered by a single 5 V. At
this voltage, the amplifier has sufficient output drive to deliver
distortion-free sound to a low impedance headphone.
L_OUT
VCC
GNDA
VREF
AD1845
R_OUT
40
35/36
32
41
10k8.66k
10k8.66k
470µF
5V
0.1µF
10µF
LEFT
CHANNEL
RIGHT
CHANNEL
0.1µF
34/37
1
2
3
5
6
7
470µF
0.1µF
10µF
1/2
SSM2135
1/2
SSM2135
4
8
AGND
00349-031
V+
Figure 31. A Stereo Headphone Driver for Multimedia Sound Codec
Figure 32 shows the total harmonic distortion characteristics vs.
frequency driving into a 32 Ω load, which is a very typical
impedance for a high quality stereo headphone. The SSM2135
has excellent power supply rejection, and, as a result, is tolerant
of poorly regulated supplies. However, for best sonic quality, the
power supply should be well regulated and heavily bypassed to
minimize supply modulation under heavy loads. A minimum of
10 μF bypass is recommended.
1
0.005
0.001
0.01
0.1
10 20k10k1k100
THD + N (%)
FREQUENCY (Hz)
V
S
= 5V
80kHz LOW-PASS FILTER
00349-032
Figure 32. Headphone Driver THD + N vs. Frequency into a 32 Ω Load
SSM2135
Rev. G | Page 11 of 16
Low Noise Microphone Preamplifier
The 5.2 nV/√Hz input noise in conjunction with low distortion
make the SSM2315 an ideal device for amplifying low level signals
such as those produced by microphones. Figure 34 illustrates a
stereo microphone input circuit feeding a multimedia sound
codec. The gain is set at 100 (40 dB), although it can be set to
other gains depending on the microphone output levels. Figure 33
shows the harmonic distortion performance of the preamplifier
with 1 V rms output, while operating from a single 5 V supply.
The SSM2135 is biased to 2.25 V by the VREF pin of the AD1845
codec. The same voltage is buffered by the 2N4124 transistor to
provide phantom power to the microphone. A typical electrets
condenser microphone with an impedance range of 100 Ω to
1 kΩ works well with the circuit. This power booster circuit can
be omitted for dynamic microphone elements.
1
0.01
0.1
10 20k10k1k100
THD + N (%)
FREQUENCY (Hz)
V
S
= 5V
A
V
= 40dB
V
OUT
= 1V rms
80kHz LOW-PASS FILTER
00349-034
Figure 33. MIC Preamp THD + N Performance
LEFT CHANNEL
MIC IN
RIGHT CHANNEL
MIC IN 2k
5V
10µF
10k
2N4124
L_MIC
V
CC
GNDA
V
REF
AD1845
R_MIC
2k
10µF
10k
10µF 0.1µF
100
10k
10010k
0.1µF
10µF
5V
2
3
4
1
8
5
6
7
5V
29
35/36
34/37
32
28
1/2
SSM2135
1/2
SSM2135
00349-033
Figure 34. Low Noise Microphone Preamp for Multimedia Sound Codec
SSM2135
Rev. G | Page 12 of 16
Single Supply Differential Line Driver
Signal distribution and routing is often required in audio systems,
particularly portable digital audio equipment for professional
applications. Figure 35 shows a single-supply line driver circuit
that has differential output. The bottom amplifier provides a
2 V dc bias for the differential amplifier to maximize the output
swing range. The amplifier can output a maximum of 0.8 V rms
signal with a 5 V supply. It is capable of driving into 600 Ω line
termination at a reduced output amplitude.
5V
1/2
SSM2135
1/2
SSM2135
AUDIO IN
100µF
1k
DIFFERENTIAL
AUDIO OUT
5V
1/2
SSM2135
1k
2.5k
100
5V
7.5k
5k
1µF
0.1µF
2V
10k
1k
10µF + 0.1µF
00349-036
Figure 35. Single-Supply Differential Line Driver
Single-Supply Differential Line Receiver
Receiving a differential signal with minimum distortion is
achieved using the circuit in Figure 36. Unlike a difference
amplifier (a subtractor), the circuit has a true balanced input
impedance regardless of input drive levels; that is, each input
always presents a 20 kΩ impedance to the source. For best
common-mode rejection performance, all resistors around the
differential amplifier must be very well matched. Best results
can be achieved using a 10 kΩ precision resistor network.
1/2
SSM2135
AUDIO
OUT
1/2
SSM2135
20k
5V
5V
1/2
SSM2135
DIFFERENTIAL
AUDIO IN
100
5k
1µF
0.1µF
2.5k
5V
7.5k
1010µF
20k
20k
2V
20k
20k
10µF + 0.1µF
00349-037
Figure 36. Single-Supply Balanced Differential Line Receiver
Pseudoreference Voltage Generator
For single-supply circuits, a reference voltage source is often
required for biasing purposes or signal offsetting purposes. The
circuit in Figure 37 provides a supply splitter function with low
output impedance. The 1 μF output capacitor serves as a charge
reservoir to handle a sudden surge in demand by the load as
well as providing a low ac impedance to it. The 0.1 μF feedback
capacitor compensates the amplifier in the presence of a heavy
capacitive load, maintaining stability.
The output can source or sink up to 12 mA of current with a
5 V supply, limited only by the 100 Ω output resistor. Reducing
the resistance increases the output current capability. Alternatively,
increasing the supply voltage to 12 V also improves the output
drive to more than 25 mA.
1/2
SSM2135
V
+ = 5V TO 12V
R3
2.5k
R4
100k
R2
5k
R1
5k
C1
0.1µF
V+
2OUTPUT
C2
1µF
0
0349-038
Figure 37. Pseudoreference Generator
SSM2135
Rev. G | Page 13 of 16
Digital Volume Control Circuit Logarithmic Volume Control Circuit
Working in conjunction with the AD7528 dual 8-bit DAC,
the SSM2135 makes an efficient audio attenuator, as shown in
Figure 38. The circuit works off a single 5 V supply. The DACs
are biased to a 2 V reference level, which is sufficient to keep
the internal R-2R ladder switches of the DACs operating prop-
erly. This voltage is also the optimal midpoint of the SSM2135
common-mode and output swing range. With the circuit as
shown in Figure 38, the maximum input and output swing is
1.25 V rms. Total harmonic distortion measures a respectable
0.01% at 1 kHz and 0.1% at 20 kHz. The frequency response at
any attenuation level is flat to 20 kHz.
Figure 39 shows a logarithmic version of the volume control
function. Similar biasing is used. With an 8-bit bus, the AD7111
provides an 88.5 dB attenuation range. Each bit resolves a 0.375 dB
attenuation. Refer to the AD7111 data sheet for attenuation levels
for each input code.
I
OUT
DATA IN
AND
CONTROL
LEFT AUDIO
IN
RIGHT AUDIO
IN
V
DD
DGND
5V
0.1µF
AGND
I
OUT
R
FB
V
DD
DGND
V
IN
AD7111
3
5V
0.1µF
3
14
14
16
16
10
10
10
47µF
47µF R
FB
AGND
V
IN
D1
D1
AD7111
5V
1/2
SSM2135
1/2
SSM2135
47µF
2k
5V
2V
7.5k
5k
100
0.1µF
1µF
2V
1/2
SSM2135
5V
47µF
1
2
1
2
RIGHT AUDIO
OUT
LEFT AUDIO
OUT
10µF + 0.1µF
00349-041
Each DAC can be controlled independently via the 8-bit parallel
data bus. The attenuation level is linearly controlled by the
binary weighting of the digital data input. Total attenuation
ranges from 0 dB to 48 dB.
5V
1/2
SSM2135
1/2
SSM2135
5V 10µF + 0.1µF
6DAC A/
DAC B
1/2
SSM2135
V
REF
A
DAC A
OUT A
R
FB
A
V
REF
B
DACB
R
FB
B
OUT B
DATA IN
15 CS
16 WR
18
CONTROL
SIGNAL
LEFT
AUDIO IN
RIGHT
AUDIO IN
V
DD
DGND
17 5
5V
0.1µF
AD7528
3
2
19
20
1
RIGHT AUDIO
OUT
LEFT AUDIO
OUT
47µF
47µF
2k
5V
2V
7.5k
5k
100
0.1µF
1µF
2V
0
0349-040
Figure 39. Single-Supply Logarithmic Volume Control
Figure 38. Digital Volume Control
SSM2135
Rev. G | Page 14 of 16
OUTLINE DIMENSIONS
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
COMPLIANT TO JEDEC STANDARDS MS-012-AA
012407-A
0.25 (0.0098)
0.17 (0.0067)
1.27 (0.0500)
0.40 (0.0157)
0.50 (0.0196)
0.25 (0.0099) 45°
1.75 (0.0688)
1.35 (0.0532)
SEATING
PLANE
0.25 (0.0098)
0.10 (0.0040)
4
1
85
5.00 (0.1968)
4.80 (0.1890)
4.00 (0.1574)
3.80 (0.1497)
1.27 (0.0500)
BSC
6.20 (0.2441)
5.80 (0.2284)
0.51 (0.0201)
0.31 (0.0122)
COPLANARITY
0.10
Figure 40. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body
(R-8)
Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model1 Temperature Range Package Description Package Option
SSM2135S −40°C to +85°C 8-Lead SOIC_N R-8
SSM2135S-REEL −40°C to +85°C 8-Lead SOIC_N R-8
SSM2135S-REEL7 −40°C to +85°C 8-Lead SOIC_N R-8
SSM2135SZ −40°C to +85°C 8-Lead SOIC_N R-8
SSM2135SZ-REEL −40°C to +85°C 8-Lead SOIC_N R-8
SSM2135SZ-REEL7 −40°C to +85°C 8-Lead SOIC_N R-8
1 Z = RoHS Compliant Part.
SSM2135
Rev. G | Page 15 of 16
NOTES
SSM2135
Rev. G | Page 16 of 16
NOTES
©2003–2011 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D00349-0-4/11(G)