Tripath Technology, Inc. - Technical Information
TJ(MAX ) − TA
PDISS
=
θ
JA
where:
PDISS = maximum power dissipation
TJMAX = maximum junction temperature of TA2022
TA = operating ambient temperature
θJA = junction-to-ambient thermal resistance
θJA = θJC + θCS + θSA
Example:
What size heat sink is required to operate the TA2022 at 80W per channel continuously in a 70ºC
ambient temperature?
P
DISS is determined by:
POUT
POUT
POUT −PDISS
Efficiency = η =
=
P
IN
POUT
η
90
0.85
PDISS (per channel) =
− POUT
=
− 90 = 15.88 W
Thus, PDISS for two channels = 31.76W
TJ(MAX ) − TA
150 − 70
31.76
θJA
=
=
= 2.52°C/W
PDISS
The θJC of the TA2022 is 1.0°C/W, so a heat sink of 1.32°C/W is required for this example (assuming
a θCS = 0.2°C/W). In actual applications, other factors such as the average PDISS with a music source
(as opposed to a continuous sine wave) and regulatory agency testing requirements will help
determine the size of the heat sink required.
Performance Measurements of the TA2022
The TA2022 operates by generating a high frequency switching signal based on the audio input. This
signal is sent through a low-pass filter (external to the Tripath amplifier) that recovers an amplified
version of the audio input. The frequency of the switching pattern is spread spectrum in nature and
typically varies between 100kHz and 1MHz, which is well above the 20Hz – 20kHz audio band. The
pattern itself does not alter or distort the audio input signal, but it does introduce some inaudible
components.
The measurements of certain performance parameters, particularly noise related specifications such
as THD+N, are significantly affected by the design of the low-pass filter used on the output as well as
the bandwidth setting of the measurement instrument used. Unless the filter has a very sharp roll-off
just beyond the audio band or the bandwidth of the measurement instrument is limited, some of the
inaudible noise components introduced by the TA2022 amplifier switching pattern will degrade the
measurement.
One feature of the TA2022 is that it does not require large multi-pole filters to achieve excellent
performance in listening tests, usually a more critical factor than performance measurements.
Though using a multi-pole filter may remove high-frequency noise and improve THD+N type
measurements (when they are made with wide-bandwidth measuring equipment), these same filters
degrade frequency response. The TA2022 Evaluation Board uses the Application/Test Circuit of this
data sheet, which has a simple two-pole output filter and excellent performance in listening tests.
Measurements in this data sheet were taken using this same circuit with a limited bandwidth setting in
the measurement instrument.
29
TA2022 – KLI/1.2/07-04
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
