Datasheet

LM4940
SNAS219C –OCTOBER 2003–REVISED MAY 2013 www.ti.com
APPLICATION INFORMATION
Figure 26. Typical LM4940 Stereo Amplifier Application Circuit
HIGH VOLTAGE BOOMER WITH INCREASED OUTPUT POWER
Unlike previous 5V Boomer amplifiers, the LM4940 is designed 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 4Ω loads with no
more than 1% THD+N.
POWER DISSIPATION
Power dissipation is a major concern when designing a successful single-ended amplifier. Equation 1 states the
maximum power dissipation point for a single-ended amplifier operating at a given supply voltage and driving a
specified output load.
P
DMAX-SE
= (V
DD
)
2
/ (2π
2
R
L
): Single Ended (1)
The LM4940's dissipation is twice the value given by Equation 1 when driving two SE loads. For a 12V supply
and two 8Ω SE loads, the LM4940's dissipation is 1.82W.
The maximum power dissipation point (twice the value given by Equation 1 must not exceed the power
dissipation given by Equation 2:
P
DMAX
' = (T
JMAX
- T
A
) / θ
JA
(2)
The LM4940's T
JMAX
= 150°C. In the KTW package, the LM4940's θ
JA
is 20°C/W when the metal tab is soldered
to a copper plane of at least 16in
2
. This plane can be split between the top and bottom layers of a two-sided
PCB. Connect the two layers together under the tab with a 5x5 array of vias. For the NEC package, use an
external heatsink with a thermal impedance that is less than 20°C/W. At any given ambient temperature T
A
, use
Equation 3 to find the maximum internal power dissipation supported by the IC packaging. Rearranging
Equation 3 and substituting P
DMAX
for P
DMAX
' results in Equation 4. This equation gives the maximum ambient
temperature that still allows maximum stereo power dissipation without violating the LM4940's maximum junction
temperature.
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