SSM2211 View Datasheet(PDF) - Analog Devices
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SSM2211 Datasheet PDF : 24 Pages
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voltage reference. The extra supply voltage also allows the
SSM2211 to reproduce peaks in excess of 1 W without clipping
the signal. With VDD = 5 V and RL = 8 Ω, Equation 9 shows that
the maximum power dissipation for the SSM2211 is 633 mW.
From the power derating curve in Figure 31, the ambient
temperature must be less than 73°C for the SOIC and 118°C for
the LFCSP.
The required gain of the amplifier can be determined from
Equation 17 as
AV =
PL × RL = 2.8
VIN,rms
(17)
From Equation 1
RF = AV
RI 2
or RF = 1.4 × RI. Because the desired input impedance is 20 kΩ,
RI = 20 kΩ and R2 = 28 kΩ.
The final design step is to select the input capacitor. When
adding an input capacitor, CC, to create a high-pass filter, the
corner frequency needs to be far enough away for the design to
meet the bandwidth criteria. For a first-order filter to achieve a
pass-band response within 0.25 dB, the corner frequency must
be at least 4.14× away from the pass-band frequency. So, (4.14 ×
fHP) < 20 Hz. Using Equation 2, the minimum size of input
capacitor can be found.
CC
>
2π
×
20
1
kΩ
⎜⎜⎝⎛
20 Hz
4.14
⎟⎟⎠⎞
(18)
Therefore, CC > 1.65 μF. Using a 2.2 μF is a practical choice for CC.
The gain bandwidth product for each internal amplifier in the
SSM2211 is 4 MHz. Because 4 MHz is much greater than
4.14 × 20 kHz, the design meets the upper frequency bandwidth
criteria. The SSM2211 can also be configured for higher
differential gains without running into bandwidth limitations.
Equation 16 shows an appropriate value for CB to reduce start-
up popping noise.
(2.2μF)(20 kΩ)
C B > 25 kΩ =1.76 μF
(19)
Selecting CB to be 2.2 μF for a practical value of capacitor
minimizes start-up popping noise.
To summarize the final design:
VDD
R1
RF
CC
CB
TA, MAX
5V
20 kΩ
28 kΩ
2.2 μF
2.2 μF
85°C
SSM2211
SINGLE-ENDED APPLICATIONS
There are applications in which driving a speaker differentially is
not practical, for example, a pair of stereo speakers where the
minus terminal of both speakers is connected to ground. Figure 48
shows how this can be accomplished.
10kΩ
5V
AUDIO
INPUT
10kΩ
0.47μF
6
4–
5
SSM2211
3+
8
1
7
2
470μF +
0.1μF
–
250mW
SPEAKER
(8Ω)
Figure 48. Single-Ended Output Application
It is not necessary to connect a dummy load to the unused
output to help stabilize the output. The 470 μF coupling
capacitor creates a high-pass frequency cutoff of 42 Hz, as given
in Equation 4, which is acceptable for most computer speaker
applications. The overall gain for a single-ended output
configuration is AV = RF/R1, which for this example is equal to 1.
DRIVING TWO SPEAKERS SINGLE ENDEDLY
It is possible to drive two speakers single endedly with both
outputs of the SSM2211.
20kΩ
AUDIO
INPUT
5V
470μF –
20kΩ
1μF
6
4–
5
SSM2211
3+
8
1
7
2
+
470μF +
0.1μF
–
LEFT
SPEAKER
(8Ω)
RIGHT
SPEAKER
(8Ω)
Figure 49. SSM2211 Used as a Dual-Speaker Amplifier
Each speaker is driven by a single-ended output. The trade-off
is that only 250 mW of sustained power can be put into each
speaker. Also, a coupling capacitor must be connected in series
with each of the speakers to prevent large dc currents from
flowing through the 8 Ω speakers. These coupling capacitors
produce a high-pass filter with a corner frequency given by
Equation 4. For a speaker load of 8 Ω and a coupling capacitor
of 470 μF, this results in a −3 dB frequency of 42 Hz.
Because the power of a single-ended output is one-quarter that
of a bridged output, both speakers together are still half as loud
(−6 dB SPL) as a single speaker driven with a bridged output.
Rev. D | Page 19 of 24
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