TPA6102A2
50mW ULTRALOW VOLTAGE, FIXEDGAIN STEREO HEADPHONE
AUDIO POWER AMPLIFIER
SLOS324B JUNE 2000 REVISED SEPTEMBER 2004
14
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
output coupling capacitor, CC
In the typical single-supply single-ended (SE) configuration, an output coupling capacitor (CC) is required to
block the dc bias at the output of the amplifier, thus preventing dc currents in the load. As with the input coupling
capacitor, the output coupling capacitor and impedance of the load form a high-pass filter governed by
equation 4.
(4)
fc +
1
2
pR
L CC
The main disadvantage, from a performance standpoint, is that the typically small load impedances drive the
low-frequency corner higher. Large values of CC are required to pass low-frequencies into the load. Consider
the example where a CC of 68 F is chosen and loads vary from 32 to 47 k. Table 1 summarizes the
frequency response characteristics of each configuration.
Table 1. Common-Load Impedances vs Low-Frequency Output Characteristics in SE Mode
RL
CC
Lowest Frequency
32
68
F
73 Hz
10,000
68
F
0.23 Hz
47,000
68
F
0.05 Hz
As Table 1 indicates, headphone response is adequate and drive into line level inputs (a home stereo for
example) is very good.
The output-coupling capacitor required in single-supply SE mode also places additional constraints on the
selection of other components in the amplifier circuit. With the rules described earlier still valid, add the following
relationship:
(5)
1
C
B
55 k
v
1
C
I RI
1
R
LCC
using low-ESR capacitors
Low-ESR capacitors are recommended throughout this application. A real capacitor can be modeled simply as
a resistor in series with an ideal capacitor. The voltage drop across this resistor minimizes the beneficial effects
of the capacitor in the circuit. The lower the equivalent value of this resistance, the more the real capacitor
behaves like an ideal capacitor.
3.3-V versus 1.6-V operation
The TPA6102A2 was designed for operation over a supply range of 1.6 V to 3.6 V. There are no special
considerations for 1.6-V versus 3.3-V operation as far as supply bypassing, gain setting, or stability. Supply
current is slightly reduced from 0.75 mA (typical) to 0.65 mA (typical). The most important consideration is that
of output power. Each amplifier can produce a maxium output voltage swing within a few hundred millivolts of
the rails with a 10-k
load. However, this voltage swing decreases as the load resistance decreases and the
rDS(on) as the output stage transistors becomes more significant. For example, for a 32- load, the maximum
peak output voltage with VDD = 1.6 V is approximately 0.7 V with no clipping distortion. This reduced voltage
swing effectively reduces the maximum undistorted output power.