SSM2211

REV. 0

–13–

will 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 would still be half as loud

(–6 dB SPL) as a single speaker driven with a bridged output.

The polarity of the speakers is important, as each output is 180

°

out of phase with the other. By connecting the minus terminal

of Speaker 1 to Pin 5, and the plus terminal of Speaker 2 to

Pin 8, proper speaker phase can be established.

The maximum power dissipation of the device can be found by

doubling Equation 11, assuming both loads are equal. If the

loads are different, use Equation 11 to find the power dissipa-

tion caused by each load, then take the sum to find the total

power dissipated by the SSM2211.

Evaluation Board

An evaluation board for the SSM2211 is available. Contact

your local sales representative or call 1-800-ANALOGD for

more information.

AUDIO

INPUT

V+

8

4

SSM2211

5

3

2

1

10 F

6

1W 8

0.1 F

+

J1

J2

0.1 F

7

20k

20k

1 f

VOLUME

20k

POT.

CW

ON

SHUTDOWN

R1

51k

+

Figure 47. Evaluation Board Schematic

The voltage gain of the SSM2211 is given by Equation 20 below:

A

R

R

V

F

IN

=×

2

(20)

If desired, the input signal may be attenuated by turning the

10 k

Ω potentiometer in the CW direction. C

common mode voltage (V+/2) present at Pin 2 and 3. With

V+ = 5 V, there is +2.5 V common-mode voltage present at

CAUTION: The ground lead of the oscilloscope probe, or any

other instrument used to measure the output signal, must not be

connected to either output, as this would short out one of the

amplifier’s outputs and possibly damage the device.

A safe method of displaying the differential output signal using a

grounded scope is shown in Figure 48. Simply connect the Chan-

Most multichannel oscilloscopes have this feature built in. If you

must connect the ground lead of the test instrument to either out-

put signal pins, a power line isolation transformer must be used

to isolate the instrument ground from power supply ground.

Recall that VP

R

=× , so for P

Ω,

V = 2.8 V rms, or 8 V p-p. If the available input signal is 1.4 V

When you have determined the closed-loop gain required by

your source level, and can develop 1 W across the 8

Ω load re-

sistor with the normal input signal level, replace the resistor

with your speaker. Your speaker may be connected across the

8

Ω load resistor is removed. For no phase inversion, V

O2

should be connected to the (+) terminal of the speaker.

8

SSM2211

5

2.5V

COMMON

MODE

8

1W

GND

CH A

CH B

PROBES

CH B

INV. ON

DISPLAY

A+B

OSCILLOSCOPE

Figure 48. Using an Oscilloscope to Display the Bridged

Output Voltage

To use the SSM2211 in a single ended output configuration,

replace J1 and J2 jumpers with electrolytic capacitors of a suit-

able value, with the NEGATIVE terminals to the output termi-

to ground. Note that the maximum output power is reduced to

250 mW, one quarter of the rated maximum, due to the maxi-

mum swing in the non-bridged mode being one-half, and power

being proportional to the square of the voltage. For frequency

response down 3 dB at 100 Hz, a 200

µF capacitor is required

with 8

Ω speakers.

The SSM2211 evaluation board also comes with a SHUT-

DOWN switch which allows the user to switch between ON

(normal operation) and the power conserving shutdown mode.

Printed Circuit Board Layout Consideration

All surface mount packages rely on the traces of the PC board

to conduct heat away from the package.

In standard packages, the dominant component of the heat re-

sistance path is the plastic between the die attach pad and the

individual leads. In typical thermally enhanced packages, one or

more of the leads are fused to the die attach pad, significantly

decreasing this component. To make the improvement mean-

ingful, however, a significant copper area on the PCB must be

attached to these fused pins.

The patented Thermal Coastline lead frame design used in the

SSM2211 (Figure 49) uniformly minimizes the value of the

dominant portion of the thermal resistance. It ensures that heat

is conducted away by all pins of the package. This yields a very

low, 98

°C/W, thermal resistance for an SO-8 package, without

any special board layer requirements, relying on the normal

traces connected to the leads. The thermal resistance can be de-

creased by approximately an additional 10% by attaching a few