SSM2211

REV. 0

–8–

TYPICAL APPLICATION

SSM2211

AUDIO

INPUT

SPEAKER

8

+5V

2

7

1 8

5

6

4

3

Figure 39. A Typical Configuration

Figure 39 shows how the SSM2211 would be connected in a

typical application. The SSM2211 can be configured for gain

much like a standard op amp. The gain from the audio input to

the speaker is:

A

R

R

V

F

I

=×

2

(1)

The

2 factor comes from the fact that Pin 8 is opposite polar-

ity from Pin 5, providing twice the voltage swing to the speaker

from the bridged output configuration.

ing. Pin 2 is connected to Pin 3 to provide an offset voltage for

ground to help power supply rejection. Because Pin 4 is a virtual

coupling capacitor which also creates a high-pass filter with a

corner frequency of:

f

RC

HP

IC

=

×

1

2

π

(2)

Because the SSM2211 has an excellent phase margin, a feed-

not required, as it is in some competitor’s products.

Bridged Output vs. Single Ended Output Configurations

The power delivered to a load with a sinusoidal signal can be ex-

pressed in terms of the signal’s peak voltage and the resistance

of the load:

P

V

R

L

PK

L

=

2

2

(3)

By driving a load from a bridged output configuration, the volt-

age swing across the load doubles. An advantage in using a

bridged output configuration becomes apparent from Equation

3 as doubling the peak voltage results in four times the power

delivered to the load. In a typical application operating from a

5 V supply, the maximum power that can be delivered by the

SSM2211 to an 8

Ω speaker in a single ended configuration is

250 mW. By driving this speaker with a bridged output, 1 W of

power can be delivered. This translates to a 12 dB increase in

sound pressure level from the speaker.

SSM2211 PRODUCT OVERVIEW

The SSM2211 is a low distortion speaker amplifier that can run

from a 1.7 V to 5.5 V supply. It consists of a rail-to-rail input

and a differential output that can be driven within 400 mV of

either supply rail while supplying a sustained output current of

350 mA. The SSM2211 is unity-gain stable, requiring no exter-

nal compensation capacitors, and can be configured for gains of

up to 40 dB. Figure 38 shows the simplified schematic.

4

3

SHUTDOWN

A2

A1

BIAS

CONTROL

2

20k

20k

50k

50k

50k

50k

0.1 F

71

8

5

6

SSM2211

Figure 38. Simplified Schematic

Pin 4 and Pin 3 are the inverting and noninverting terminals to A1.

An offset voltage is provided at Pin 2, which should be connected

to Pin 3 for use in single supply applications. The output of A1

appears at Pin 5. A second op amp, A2, is configured with a fixed

The SSM2211 outputs at Pins 5 and 8 produce a bridged configu-

ration output to which a speaker can be connected. This bridge

configuration offers the advantage of a more efficient power trans-

fer from the input to the speaker. Because both outputs are sym-

metric, the dc bias at Pins 5 and 8 are exactly equal, resulting in

zero dc differential voltage across the outputs. This eliminates the

need for a coupling capacitor at the output.

The SSM2211 can achieve 1 W continuous output into 8

Ω, even

at ambient temperatures up to +85

°C. This is due to a propri-

etary SOIC package from Analog Devices that makes use of an

internal structure called a Thermal Coastline. The Thermal

Coastline provides a more efficient heat dissipation from the die

than in standard SOIC packages. This increase in heat dissipation

allows the device to operate in higher ambient temperatures or at

higher continuous output currents without overheating the die.

For a standard SOIC package, typical junction to ambient tem-

°C/W. In a Thermal

Thermal Coastline package will not get as hot as a die in a stan-

dard SOIC package at the same current output.

Because of the large amounts of power dissipated in a speaker

amplifier, competitor’s parts operating from a 5 V supply can

only drive 1 W into 8

Ω in ambient temperatures less than

+44

°C, or +111°F. With the Thermal Coastline SOIC package,

the SSM2211 can drive an 8

Ω speaker with 1 W from a 5 V

supply with ambient temperatures as high as +85

°C (+185°F),

without a heat sink or forced air flow.