SSM2211_04 데이터 시트보기 (PDF) - Analog Devices
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SSM2211_04 Datasheet PDF : 20 Pages
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SSM2211
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, high-pass filter, the corner fre-
quency 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 should
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
>
2 π(20
1
kΩ)⎜⎛ 20Hz ⎟⎞
(18)
⎝ 4.14 ⎠
So 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 could 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:
CB
>
(2.2
µF)(20
25 kΩ
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
5V
R1
20 kΩ
RF
28 kΩ
CC
2.2 µF
CB
2.2 µF
Max. TA 85°C
SINGLE-ENDED APPLICATIONS
There are applications in which driving a speaker differentially
is not practical. An example would be 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. A 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, as given in
Equation 4, of 42 Hz, 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.
The polarity of the speakers is important, as each output is 180°
out of phase with the other. By connecting the minus terminal
of Speaker 1 to Pin 5, and the plus terminal of Speaker 2 to Pin
8, proper speaker phase can be established.
Rev. C | Page 18 of 20
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