Tripath Technology, Inc. - Technical Information
Application Information
Amplifier Gain and Input Resistor Selection
The value of the input resistor, RIN, is based on the required voltage gain, AV, of the amplifier
according to:
AV = 538 x103/(RIN + 5000)
where RIN = Input resistor value in ohms.
Input Capacitor Selection
CIN can be calculated once a value for RIN has been determined. CIN and RIN determine the input
low-frequency pole. Typically this pole is set at 10 Hz. CIN is calculated according to:
CIN = 1/((2π x FP)(RIN + 5000))
where:
RIN = Input resistor value in ohms.
FP = Input low frequency pole (typically 10Hz).
DC Offset Adjust
While the DC offset voltages that appear at the speaker terminals of a TA0103A amplifier are
typically small, Tripath recommends that any offsets during operation be nulled out of the amplifier
with a circuit like the one shown connected to IN1 and IN2 in the Test/Application Circuit.
It should be noted that the DC voltage on the output of a TA0103A amplifier with no load in mute
mode is approximately 2.5V. This offset does not need to be nulled. The output impedance of the
amplifier in mute mode is approximately 10 KOhms. This means that the 2.5V drops to essentially
zero when a typical load is connected.
Supply Voltage and Output Power
The relationship between the bipolar power supply voltage needed, VS, for a given RMS output
power, POUT, into a given load, RL, at a given level of THD (total harmonic distortion) is approximated
by:
VS = (2 x RL x POUT) 0.5/(K x RL/(RL + RON + RS + RCOIL))
where:
RON = The at-temperature RDSON of the output transistors, M.
RCOIL = Resistance of the output filter inductor.
RS = Sense Resistor
K = THD Factor, a number fixed by the algorithms in the TA0103A’s signal processor that
provides the relationship between THD at full output power of the amplifier and VS. K
corresponds to THD at full output power as follows:
THD
K
0.1%
0.83
1%
0.95
10%
1.09
Typical measurement graphs of POUT versus supply voltage for various levels of THD are also
included in this data sheet to help determine the supply voltage.
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TA0103 – Rev 3.3/06.00