SSM2211

Rev. D | Page 19 of 24

voltage reference. The extra supply voltage also allows the

SSM2211 to reproduce peaks in excess of 1 W without clipping

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

8

.

2

=

×

=

rms

IN,

L

L

V

V

R

P

A

(17)

From Equation 1

2

V

I

F

A

R

R =

The final design step is to select the input capacitor. When

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 ×

capacitor can be found.

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

×

>

14

4

Hz

20

kΩ

20

π

2

1

.

C

C

(18)

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.

up popping noise.

(

)(

)

μF

76

1

kΩ

25

kΩ

20

μF

2

2

.

.

C

B

=

>

(19)

minimizes start-up popping noise.

To summarize the final design:

5 V

R1

20 kΩ

28 kΩ

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.

SSM2211

5V

2

7

1

8

5

6

4

3

0.47

μF

470

μF +

–

+

–

10k

Ω

10k

Ω

250mW

SPEAKER

(8

Ω)

AUDIO

INPUT

0.1

μF

SSM2211

5V

2

7

1

8

5

6

4

3

0.47

μF

470

μF +

–

+

–

10k

Ω

10k

Ω

250mW

SPEAKER

(8

Ω)

AUDIO

INPUT

0.1

μF

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

DRIVING TWO SPEAKERS SINGLE ENDEDLY

It is possible to drive two speakers single endedly with both

outputs of the SSM2211.

SSM2211

5V

2

7

1

8

5

6

4

3

1

μF

470

μF +

–

+

–

20k

Ω

20k

Ω

RIGHT

SPEAKER

(8

Ω)

AUDIO

INPUT

0.1

μF

470

μF

LEFT

SPEAKER

(8

Ω)

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.

C

2.2 μF

2.2 μF

85°C