ssm2211z-eval Analog Devices, Inc., ssm2211z-eval Datasheet - Page 19

• Manufacturer Part Number: ssm2211z-eval
• Description: Low Distortion 1.5 Watt Audio Power Amplifier
• Manufacturer: Analog Devices, Inc.

voltage reference. The extra supply voltage also allows the
SSM2211 to reproduce peaks in excess of 1 W without clipping
the signal. With V
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
From Equation 1
or R
R
The final design step is to select the input capacitor. When
adding an input capacitor, C
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 ×
f
capacitor can be found.
Therefore, 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
up popping noise.
Selecting C
minimizes start-up popping noise.
To summarize the final design:
V
R1
R
C
C
T
HP
A, MAX
I
F
C
B
DD
= 20 kΩ and R2 = 28 kΩ.
) < 20 Hz. Using Equation 2, the minimum size of input
F
C
C
A
R
= 1.4 × R
R
V
F
C
B
I
=
>
>
=
5 V
20 kΩ
28 kΩ
2.2 μF
2.2 μF
85°C
(
π 2
A
B
2
2
C
V
P
V
.
to be 2.2 μF for a practical value of capacitor
2
> 1.65 μF. Using a 2.2 μF is a practical choice for C
L
IN,
×
μF
I
×
25
. Because the desired input impedance is 20 kΩ,
rms
20
R
)(
kΩ
DD
L
20
kΩ
1
=
= 5 V and R
kΩ
⎛
⎜ ⎜
⎝
2
20
8 .
4
)
.
=
14
Hz
1
C
.
76
, to create a high-pass filter, the
⎞
⎟ ⎟
⎠
μF
L
= 8 Ω, Equation 9 shows that
B
to reduce start-
(17)
(18)
(19)
Rev. D | Page 19 of 24
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
minus terminal of both speakers is connected to ground. Figure 48
shows how this can be accomplished.
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 A
DRIVING TWO SPEAKERS SINGLE ENDEDLY
It is possible to drive two speakers single endedly with both
outputs of the SSM2211.
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.
AUDIO
AUDIO
AUDIO
INPUT
INPUT
INPUT
Figure 49. SSM2211 Used as a Dual-Speaker Amplifier
0.47μF
0.47μF
1μF
Figure 48. Single-Ended Output Application
20kΩ
10kΩ
10kΩ
0.1μF
0.1μF
0.1μF
V
= R
F
4
3
4
4
3
3
/R
–
+
–
–
+
+
1
SSM2211
SSM2211
SSM2211
2
2
2
, which for this example is equal to 1.
20kΩ
10kΩ
10kΩ
6
6
6
5V
5V
5V
7
7
7
1
1
1
5
8
5
5
8
8
470μF
470μF
470μF
470μF
–
+
+
–
+
+
–
–
SSM2211
LEFT
SPEAKER
(8Ω)
RIGHT
SPEAKER
(8Ω)
250mW
250mW
SPEAKER
SPEAKER
(8Ω)
(8Ω)