Tripath Technology, Inc. - Technical Information
O u t pu t Fi lt e r D e s i g n
Tripath amplifiers generally have a higher switching frequency than PWM implementations, allowing
the use of higher cutoff frequency filters and reducing the load dependent peaking/drooping in the
20kHz audio band. This is especially important for applications where the end customer may attach
any speaker to the amplifier (as opposed to a system where speakers are shipped with the amplifier),
since speakers are not purely resistive loads and the impedance they present changes over
frequency and from speaker model to speaker model. An RC network, or “Zobel” (RZ, CZ) should be
placed at the filter output to control the impedance “seen” by the TP2050 when not attached to a
speaker load. The TP2050 works well with a 2nd order, 80kHz LC filter with LO = 10uH and CO =
0.47uF and RZ = 10 Ohm/1W and CZ = 0.47uF.
NOTE: Output inductor selection is a critical design step. The core material and geometry of the
output filter inductor affects the TP2050 distortion levels, efficiency, power dissipation and EMI output.
Please contact Tripath Applications for additional information about recommended inductor sources.
P r o t ect i o n C i r cu i t s
The TP2050 is protected against over-current, over / under-voltage and over-temperature conditions.
O ve r-te mp eratu r e Pr o tectio n
An over-temperature fault occurs if the junction temperature of the part exceeds approximately
150°C. The thermal hysteresis of the part is approximately 25°C, therefore the fault will automatically
clear when the junction temperature drops below 125°C.
Perfo rm an ce Mea su r emen ts o f th e T K205 0
The TP2050 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 TP2050 amplifier switching pattern will degrade the
measurement.
One feature of the TP2050 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 TP2050 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.
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TP2050– KL/1.0/07.05
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
