Data Sheet
Maximum Gain
Mute Operation
As shown in block diagram(page 2),the PAM8403
has two internal amplifiers stage. The first
stage's gain is externally configurable, while the
second stage's is internally fixed in a fixed-gain,
inverting configuration. The closed-loop gain of
the first stage is set by selecting the ratio of R to
R while the second stage's gain is fixed at
1.4x.The output of amplifier one serves as the
input to amplifier two which results in both
amplifiers producing signals identical in
magnitude, but out of phase by 180°.
Consequently, the differential gain for the IC is
A =20*log [2*(R /R )*1.4]
The PAM8403 sets maximum R =85K , minimum
R =15K , so the maximum closed-gain is 24dB.
The pin is an input for controlling the
output state of the PAM8403. A logic low on this
pin disables the outputs, and a logic high on this
pin enables the outputs. This pin may be used as
a quick disable or enable of the outputs without a
volume fade. Quiescent current is listed in the
electrical characteristic table. The pin can
be left floating due to the pull-up internal.
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VD f i
f
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Ω
Ω
MUTE
MUTE
Shutdown operation
Power supply decoupling
Input Capacitor (C )
Analog Reference Bypass Capacitor (C )
In order to reduce power consumption while not
in use, the PAM8403 contains shutdown circuitry
that is used to turn off the amplifier's bias
circuitry. This shutdown feature turns the
amplifier off when logic low is placed on the
pin. By switching the pin connected
to GND, the PAM8403 supply current draw will be
minimized in idle mode. The pin can be left
floating due to the pull-up internal.
The PAM8403 is a high performance CMOS
audio amplifier that requires adequate power
supply decoupling to ensure the output THD and
PSRR are as low as possible. Power supply
decoupling is affecting low frequency response.
Optimum decoupling is achieved by using two
capacitors of different types that target different
types of noise on the power supply leads. For
higher frequency transients, spikes, or digital
hash on the line, a good low equivalent-series-
resistance (ESR) ceramic capacitor, typically
1.0μF, placed as close as possible to the device
V terminal works best. For filtering lower-
frequency noise signals, a larger capacitor of
20μF(ceramic) or greater placed near the audio
power amplifier is recommended.
Large input capacitors are both expensive and
space hungry for portable designs. Clearly, a
certain sized capacitor is needed to couple in low
frequencies without severe attenuation. But in
many cases the speakers used in portable
systems, whether internal or external, have little
ability to reproduce signals below 100Hz to
150Hz. Thus, using a large input capacitor may
not increase actual system performance. In this
case, input capacitor (C ) and input resistance
(R ) of the amplifier form a high-pass filter with
the corner frequency determined equation below,
In addition to system cost and size, click and pop
performance is affected by the size of the input
coupling capacitor, C . A larger input coupling
capacitor requires more charge to reach its
quiescent DC voltage (nominally 1/2 V ). This
charge comes from the internal circuit via the
feedback and is apt to create pops upon device
enable. Thus, by minimizing the capacitor size
based on necessary low frequency response,
turn-on pops can be minimized.
The Analog Reference Bypass Capacitor (C ) is
the most critical capacitor and serves several
important functions. During start-up or recovery
from shutdown mode, C determines the rate at
which the amplifier starts up. The second
function is to reduce noise produced by the
power supply caused by coupling into the output
drive signal. This noise is from the internal
analog reference to the amplifier, which appears
as degraded PSRR and THD+N.
Bypass capacitor (C ) values of 0.47μF to
1.0μF ceramic is recommended for the best THD
and noise performance. Increasing the bypass
capacitor reduces clicking and popping noise
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English:www.poweranalog.com www.power-analog.com：
Application Information
PAM8403
Filterless 3W Class-D Stereo Audio Amplifier
C
ii
1
f=
2πR C
03/2007
,Power Analog Microelectronics Inc