SSM2250

Rev. A | Page 8 of 12

NC

NC

NC

LEFT IN

RIGHT IN

SHUTDOWN

5V

BTL

OUT

5V

100k

Ω

+

–

+

220

μF

+

220

μF

1k

Ω

1k

Ω

1

μF

1

μF

R1

20k

Ω

10

μF

R2

20k

Ω

R2

20k

Ω

R1

20k

Ω

SSM2250

5

14

1

2

3

4

13

12

11

10

6

7

9

8

NC

NC = NO CONNECT

NC

Figure 14. Typical Application

The output coupling capacitor creates a high-pass filter with a

cutoff frequency of

C

L

dB

C

R

f

π

=

−

2

1

3

(2)

where:

Although a majority of headphones have approximately 80 Ω of

resistance, the resistance can vary between models and manu-

facturers. Headphone resistances are commonly between 32 Ω

to 600 Ω. Using a 220 μF capacitor, as shown in Figure 14, the

worst-case −3 dB corner frequency would be 22 Hz, with a 32 Ω

headphone load. Smaller output capacitors could be used at the

expense of low frequency response to the headphones.

An input coupling capacitor should be used to remove dc bias

from the inputs to the SSM2250. Again, the input coupling

capacitor in combination with the input resistor creates a high-

pass filter with a corner frequency of

1

1

2

1

3

C

R

f

dB

π

=

−

(3)

Using the values shown in Figure 14, where R1 = 20 kΩ and

C1 = 1 μF, creates a corner frequency of 8 Hz. This is acceptable,

as the PC99 audio requirement specifies the computer audio

system bandwidth to be 20 Hz to 20 kHz.

Pin 10 on the SSM2250 provides the proper bias voltage for

the amplifiers. A 0.1 μF capacitor should be connected here to

reduce sensitivity to noise on the power supply. A larger capaci-

tor can be used if more rejection from power supply noise is

required.

The SSM2250 has excellent phase margin and is stable even

under heavy loading. Therefore, a feedback capacitor in parallel

with R2 is not required, as it is in some competitors’ products.

Power Dissipation

An important advantage in using a bridged output configura-

tion is that bridged output amplifiers are more efficient than

single-ended amplifiers in delivering power to a load.

OUTPUT POWER (W)

1.50

1.25

1.00

0.75

0.50

0.25

0

0

0.75

0.50

0.25

1.00

1.25

1.50

Figure 15. Power Dissipation vs. Output Power in BTL Mode

L

DD

MAX

,

DISS

R

V

P

2

2

2

π

=

(4)

Using Equation 4 and the power derating curve in Figure 17,

the maximum ambient temperature can be easily found. This

ensures that the SSM2250 does not exceed its maximum

junction temperature of 150°C.

The power dissipation for a single-ended output application

where an output coupling capacitor is used is shown in

Figure 16.