SSM2211

REV. 0

–10–

OUTPUT POWER – W

1.5

0

0

1.5

0.5

1.0

1.0

0.5

Figure 41. Power Dissipation vs. Output Power

Because the efficiency of a bridged output amplifier (Equation 3

power dissipated internally by the device stays relatively flat, and

will actually decrease with higher output power. The maximum

power dissipation of the device can be found by differentiating

Equation 7 with respect to load power, and setting the derivative

equal to zero. This yields:

∂

∂π

P

P

V

R

P

DISS

L

DD

L

L

=

×

−=

−

2

10

1

2

(8)

And this occurs when:

P

V

R

DISS MAX

DD

L

,

=

2

2

2

π

(9)

Using Equation 9 and the power derating curve in Figure 28,

the maximum ambient temperature can be easily found. This

insures that the SSM2211 will not exceed its maximum junction

temperature of 150

°C.

The power dissipation for a single ended output application

where the load is capacitively coupled is given by:

∂

π

P

V

R

PP

DISS

DD

L

LL

=

×

−

22

(10)

The graph of Equation 10 is shown in Figure 42.

OUTPUT POWER – W

0.35

0.30

0

0

0.4

0.1

0.2

0.3

0.20

0.15

0.10

0.05

0.25

Figure 42. Power Dissipation vs. Single Ended Output

The maximum power dissipation for a single ended output is:

P

V

R

DISS MAX

DD

L

,

=

2

2

2

π

(11)

Output Voltage Headroom

The outputs of both amplifiers in the SSM2211 can come to

within 400 mV of either supply rail while driving an 8

Ω load.

As compared to other competitors’ equivalent products, the

SSM2211 has a higher output voltage headroom. This means

that the SSM2211 can deliver an equivalent maximum output

power while running from a lower supply voltage. By running at

a lower supply voltage, the internal power dissipation of the de-

vice is reduced, as can be seen from Equation 9. This extended

output headroom, along with the Thermal Coastline package,

allows the SSM2211 to operate in higher ambient temperatures

than other competitors’ devices.

The SSM2211 is also capable of providing amplification even at

supply voltages as low as 1.7 V. Of course, the maximum power

available at the output is a function of the supply voltage.

Therefore, as the supply voltage decreases, so does the maxi-

mum power output from the device. Figure 43 shows the maxi-

mum output power versus supply voltage at various bridged-tied

load resistances. The maximum output power is defined as the

point at which the output has 1% THD.

SUPPLY VOLTAGE – V

0

1.5

5.0

2.0

2.5

3.0

3.5

4.0

4.5

1.6

1.0

0.8

0.4

0.2

1.4

1.2

0.6