SSM2211x Analog Devices, SSM2211x Datasheet - Page 12

• Manufacturer Part Number: SSM2211x
• Description: Low Distortion 1.5 Watt Audio Power Amplifier
• Manufacturer: Analog Devices

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SSM2211
For an application where R1 = 10 k and C
midrail bypass capacitor, C
mize start-up popping noise.
SSM2211 Amplifier Design Example
Given:
Maximum Output Power 1 W
Input Impedance
Load Impedance
Input Level
Bandwidth
The configuration shown in Figure 39 will be used. The first
thing to determine is the minimum supply rail necessary to ob-
tain the specified maximum output power. From Figure 43, for
1 W of output power into an 8
be at least 4.6 V. A supply rail of 5 V can be easily obtained
from a voltage reference. The extra supply voltage will also al-
low the SSM2211 to reproduce peaks in excess of 1 W without
clipping the signal. With V
shows that the maximum power dissipation for the SSM2211 is
633 mW. From the power derating curve in Figure 28, the am-
bient temperature must be less than +85 C.
The required gain of the amplifier can be determined from
Equation 17:
From Equation 1,
sired input impedance is 20 k , R1 = 20 k and R2 = 28 k .
The final design step is to select the input capacitor. Because add-
ing an input capacitor, C
needs to be far enough away for the design to meet the bandwidth
criteria. For a 1st order filter to achieve a passband response
within 0.25 dB, the corner frequency should be at least 4.14 times
away from the passband frequency. So, (4.14
Using Equation 2, the minimum size of input capacitor can be
found:
So C
The gain-bandwidth product for each internal amplifier in the
SSM2211 is 4 MHz. Because 4 MHz is much greater than
4.14
width criteria. The SSM2211 could also be configured for higher
differential gains without running into bandwidth limitations.
Equation 16 shows an appropriate value for C
up popping noise:
C
> 1.65 F. Using a 2.2 F is a practical choice for C
20 kHz, the design will meet the upper frequency band-
C
B
C
R
R
C
F
1
2 2
C
2 20
, high pass filter, the corner frequency
A
25
A
2
DD
V
F
B
20 Hz – 20 kHz
V
20 k
8
1 V rms
, should be at least 0.1 F to mini-
, or R
k
= 5 V and R
20
k
V
load, the supply voltage must
k
P R
1
IN rms
L
F
20
4 14
L
1 4
Hz
1 76
L
2 8
= 8 , Equation 9
C
R
= 0.22 F, the
B
1 . Since the de-
f
F
0.25 dB
HP
to reduce start-
) < 20 Hz.
C
.
(17)
(18)
(19)
–12–
Selecting C
minimize start-up popping noise.
To summarize the final design:
V
R1
R
C
C
Max. T
Single Ended Applications
There are applications where 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 45 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 F coupling capacitor cre-
ates 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
A
Driving Two Speakers Single Endedly
It is possible to drive two speakers single endedly with both out-
puts of the SSM2211.
Each speaker is driven by a single ended output. The trade-off
is that only 250 mW 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
DD
F
V
C
B
Figure 46. SSM2211 Used as a Dual Speaker Amplifier
AUDIO
INPUT
AUDIO
INPUT
= R
Figure 45. A Single Ended Output Application
F
A
/R1, which for this example is equal to 1.
B
5 V
20 k
28 k
2.2 F
2.2 F
+85 C
to be 2.2 F for a practical value of capacitor will
0.47 F
1 F
10k
0.1 F
20k
0.1 F
speakers. These coupling capacitors
4
3
4
3
SSM2211
SSM2211
10k
2
20k
2
+5V
6
+5V
6
7
7
1 8
1 8
5
5
470 F
470 F
470 F
250mW
SPEAKER
(8 )
LEFT
SPEAKER
(8 )
RIGHT
SPEAKER
(8 )
REV. 0