SSM2211_15 datasheet(19/24 Pages) AD

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Data Sheet

SSM2211

Rev. F | 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 signal. With VDD = 5 V and RL = 8 Ω, Equation 9 shows that

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 50°C for the SOIC and 121°C for

the LFCSP.

The required gain of the amplifier can be determined from

Equation 17 as

rms

IN,

(17)

From Equation 1

R =

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, to create a high-pass filter, the

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. Therefore,

(4.14 × fHP) < 20 Hz. Using Equation 2, the minimum size of an

input capacitor can be found.













kΩ

(18)

Therefore, 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 can 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.

(

)(

)

μF

kΩ

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 = 5 V

R1 = 20 kΩ

RF = 28 kΩ

CC = 2.2 µF

CB = 2.2 µF

TA, 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 can be accomplished.

SSM2211

0.47

µF

470

µF +

–

10k

Ω

10k

Ω

250mW

SPEAKER

Ω)

AUDIO

INPUT

0.1

µF

SSM2211

0.47

µF

470

µF +

–

10k

Ω

10k

Ω

250mW

SPEAKER

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 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 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.

SSM2211

µF

470

µF +

–

20k

Ω

20k

Ω

RIGHT

SPEAKER

Ω)

AUDIO

INPUT

0.1

µF

470

µF

LEFT

SPEAKER

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. 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.

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