Application Information

HIGH VOLTAGE BOOMER WITH INCREASED OUTPUT

POWER

signed to operate over a power supply voltages range of 10V

to 15V. Operating on a 12V power supply, the LM4940 will

deliver 3.1W per channel into 4

Ω loads with no more than

1% THD+N.

POWER DISSIPATION

Power dissipation is a major concern when designing a

successful single-ended amplifier. Equation (2) states the

maximum power dissipation point for a single-ended ampli-

fier operating at a given supply voltage and driving a speci-

fied output load.

P

Single Ended

(1)

The LM4940’s dissipation is twice the value given by Equa-

tion (2) when driving two SE loads. For a 12V supply and two

8

Ω SE loads, the LM4940’s dissipation is 1.82W.

The maximum power dissipation point (twice the value given

by Equation (2)) must not exceed the power dissipation

given by Equation (4):

P

θ

JA

(2)

The LM4940’s T

LM4940’s

θ

copper plane of at least 16in

tween the top and bottom layers of a two-sided PCB. Con-

nect the two layers together under the tab with a 5x5 array of

vias. For the TA package, use an external heatsink with a

thermal impedance that is less than 20˚C/W. At any given

ambient temperature T

mum internal power dissipation supported by the IC packag-

ing. Rearranging Equation (4) and substituting P

P

mum ambient temperature that still allows maximum stereo

power dissipation without violating the LM4940’s maximum

junction temperature.

T

θ

JA

(3)

For a typical application with a 12V power supply and two 4

Ω

SE loads, the maximum ambient temperature that allows

maximum stereo power dissipation without exceeding the

maximum junction temperature is approximately 113˚C for

the TS package.

T

θ

(4)

Equation (6) gives the maximum junction temperature

T

maximum junction temperature by reducing the power sup-

ply voltage or increasing the load resistance. Further allow-

ance should be made for increased ambient temperatures.

The above examples assume that a device is operating

around the maximum power dissipation point. Since internal

power dissipation is a function of output power, higher am-

bient temperatures are allowed as output power or duty

cycle decreases.

20075672

FIGURE 3. Typical LM4940 Stereo Amplifier Application Circuit

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