T E C H N I C A L I N F O R M A T I O N
The θJA of the TA2020-020 in free air is 15°C/W. The θJC of the TA2020-020 is 3.5°C/W, so a heat
sink of 4.5°C/W is required for this example. 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 determine the size of the heat sink required.
Performance Measurements of the TA2020-020
The TA2020-020 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 TA2020-020 amplifier switching pattern
will degrade the measurement.
One feature of the TA2020-020 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 TA2020-020 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.
TA2020-020, Rev. 4.0, 09.00
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TRIPATH [ TRIPATH TECHNOLOGY INC. ]
