Datasheet

SSM2211 Data Sheet
Rev. G | Page 20 of 24
The final design step is to select the input capacitor. When
adding an input capacitor, C
C
, to create a high-pass filter, the
corner frequency must 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. Therefore,
(4.14 × f
HP
) < 20 Hz. Using Equation 2, the minimum size of an
input capacitor can be found.








×
>
144
Hz20
kΩ20π2
1
.
C
C
(18)
Therefore, C
C
> 1.65 µF. Using a 2.2 µF is a practical choice for C
C
.
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 C
B
to reduce start-up popping noise.
( )( )
μF761
kΩ25
kΩ20μF22
.
.
C
B
=>
(19)
Selecting C
B
to be 2.2 µF for a practical value of capacitor
minimizes start-up popping noise.
To summarize the final design,
• V
DD
= 5 V
• R1 = 20 kΩ
• R
F
= 28 kΩ
• C
C
= 2.2 µF
• C
B
= 2.2 µF
• T
A, MAX
= 85°C
SINGLE-ENDED APPLICATIONS
There are applications in which driving a speaker differentially
is not practical, for example, a pair of stereo speakers where the
negative terminal of both speakers is connected to ground.
Figure 48 shows how this application can be accomplished.
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 capa-
citor 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 config-
uration is A
V
= R
F
/R
1
, 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.
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. In addition, 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 BTL, both speakers together are still half as loud (−6 dB SPL) as
a single speaker driven with a BTL.
The polarity of the speakers is important because each output is
180° out of phase with the other. By connecting the negative
terminal of Speaker 1 to Pin 5 and the positive terminal of
Speaker 2 to Pin 8, proper speaker phase can be established.
The maximum power dissipation of the device, assuming both
loads are equal, can be found by doubling Equation 11. If the
loads are different, use Equation 11 to find the power dissipa-
tion caused by each load, and then take the sum to find the total
power dissipated by the SSM2211.
SSM2211
5V
2
7
1
8
5
6
4
3
0.47µF
470µF
+
–
+
–
10kΩ
10kΩ
250mW
SPEAKER
(8Ω)
AUDIO
INPUT
0.1µF
00358-048
SSM2211
5V
2
7
1
8
5
6
4
3
0.47µF
470µF
+
–
+
–
10kΩ
10kΩ
250mW
SPEAKER
(8Ω)
AUDIO
INPUT
0.1µF
00358-048
SSM2211
5V
2
7
1
8
5
6
4
3
1µF
470µF
+
–
+
–
20kΩ
20kΩ
RIGHT
SPEAKER
(8Ω)
AUDIO
INPUT
0.1µF
00358-049
470µF
+
–
LEFT
SPEAKER
(8Ω)