TPA005D14
2-W STEREO CLASS-D AUDIO POWER AMPLIFIER
SLOS240A – AUGUST 1999 – REVISED MARCH 2000
17
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
mute and shutdown modes
The TPA005D14 employs both a mute and a shutdown mode of operation designed to reduce supply current,
I
DD
, to the absolute minimum level during periods of nonuse for battery-power conservation. The SHUTDOWN
input terminal should be held high during normal operation when the amplifier is in use. Pulling SHUTDOWN
low causes the outputs to mute and the amplifier to enter a low-current state, I
DD
= 0.2
μ
A. Mute mode alone
reduces I
DD
to 10 mA.
using low-ESR capacitors
Low-ESR capacitors are recommended throughout this applications section. A real (as opposed to ideal)
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.
output filter components
The output inductors are key elements in the performance of the class-D audio amplifier system. It is important
that these inductors have a high enough current rating and a relatively constant inductance over frequency and
temperature. The current rating should be higher than the expected maximum current to avoid magnetically
saturating the inductor. When saturation occurs, the inductor loses its functionality and looks like a short circuit
to the PWM signal, which increases the harmonic distortion considerably.
A shielded inductor may be required if the class-D amplifier is placed in an EMI sensitive system; however, the
switching frequency is low for EMI considerations and should not be an issue in most systems. The dc series
resistance of the inductor should be low to minimize losses due to power dissipation in the inductor, which
reduces the efficiency of the circuit.
Capacitors are important in attenuating the switching frequency and high frequency noise, and in supplying
some of the current to the load. It is best to use capacitors with low equivalent-series-resistance (ESR). A low
ESR means that less power is dissipated in the capacitor as it shunts the high-frequency signals. Placing these
capacitors in parallel also parallels their ESR, effectively reducing the overall ESR value. The voltage rating is
also important, and, as a rule of thumb, should be 2 to 3 times the maximum rms voltage expected to allow for
high peak voltages and transient spikes. These output filter capacitors should be stable over temperature since
large currents flow through them.
For 8-
loads, double the inductor value and halve the common-mode capacitors (i.e., 15
μ
H to 30
μ
H). For
more information, see application report SLOA023, Reducing and Eliminating the Class-D Output Filterand
application report SLOA031, Design Considerations for Class-D Audio Power Amplifiers