SSM2211

REV. 0

–12–

For an application where R1 = 10 k

Ω and C

µF to mini-

mize start-up popping noise.

SSM2211 Amplifier Design Example

Given:

Maximum Output Power

1 W

Input Impedance

20 k

Ω

Load Impedance

8

Ω

Input Level

1 V rms

Bandwidth

20 Hz – 20 kHz

± 0.25 dB

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

Ω load, the supply voltage must

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

Ω, Equation 9

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:

A

PR

V

V

LL

IN rms

==

,

.

28

(17)

From Equation 1,

R

R

A

FV

12

=

, or RR

14

1

.

. Since the de-

sired input impedance is 20 k

Ω, R1=20kΩ and R2 = 28 kΩ.

The final design step is to select the input capacitor. Because add-

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:

C

k

Hz

Ω

()









1

220

20

414

π

.

(18)

µF. Using a 2.2 µF is a practical choice for 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 will meet the upper frequency band-

width criteria. The SSM2211 could also be configured for higher

differential gains without running into bandwidth limitations.

up popping noise:

C

Fk

k

F

µ

()

Ω

=µ

22

20

25

176

.

.

(19)

minimize start-up popping noise.

To summarize the final design:

5V

R1

20 k

Ω

28 k

Ω

2.2

µF

2.2

µF

+85

°C

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.

SSM2211

AUDIO

INPUT

250mW

SPEAKER

(8 )

10k

+5V

2

7

1 8

5

6

4

3

0.1 F

0.47 F

470 F

10k

Figure 45. A 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 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

Driving Two Speakers Single Endedly

It is possible to drive two speakers single endedly with both out-

puts of the SSM2211.

SSM2211

AUDIO

INPUT

RIGHT

SPEAKER

(8 )

20k

+5V

2

7

1 8

5

6

4

3

0.1 F

1 F

470 F

20k

LEFT

SPEAKER

(8 )

470 F

Figure 46. SSM2211 Used as a Dual Speaker Amplifier

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

Ω speakers. These coupling capacitors