PAM8302A_13 Datasheet, PDF (9/15 Pages) Power Analog Micoelectronics – 2.5W Filterless Class-D Mono Audio Amplifier

PAM8302A
2.5W Filterless Class-D Mono Audio Amplifier
Application Information
Maximum Gain
As shown in block diagram (page 2), the
PAM8302A has two internal amplifier stages. The
first stage's gain is externally configurable, while
the second stage's is internally fixed. The closed-
loop gain of the first stage is set by selecting the
ratio of R_f to R_i while the second stage's gain is
fixed at 2x.The output of amplifier 1 serves as the
input to amplifier 2, thus the two amplifiers
produce signals identical in magnitude, but
different in phase by 180°. Consequently, the
differential gain for the IC is
A_VD=20*log [2*(R_f/R_i)]
The PAM8302A sets maximum R_f=80kΩ, minimum
R_i=10kΩ, so the maximum closed-gain is 24dB.
Input Capacitors (Ci)
In typical application, an input capacitor, Ci, is
required to allow the amplifier to bias input
signals to a proper DC level for optimum
operation. In this case, Ci and the minimum input
impedance Ri (10k internal) form a high pass filter
with a corner frequency determined by the
following equation:
1
fC =
( 2p RiCi)
It is important to choose the value of Ci as it
directly affects low frequency performance of the
circuit, for example, when an application requires
a flat bass response as low as 100Hz. Equation is
reconfigured as follows:
1
Ci =
( 2pRifc )
As the input resistance is variable, for the Ci
value of 0.16μF, one should actually choose the
Ci within the range of 0.1μF to 0.22μF. A further
consideration for this capacitor is the leakage
path from the input source through the input
network (Ri, RF,Ci) to the load. This leakage
current creates a DC offset voltage at the input to
the amplifier that reduces useful headroom,
especially in high gain application. For this
reason, a low leakage tantalum or ceramic
capacitor is the best choice. When a polarized
capacitor is used, the positive side of the
capacitor should face the amplifier input in most
applications as the DC level is held at VDD/2,
which is likely higher than the source DC level.
Please note that it is important to confirm the
capacitor polarity in the application.
Power Supply Decoupling (Cs)
The PAM8302A is a high-performance CMOS
audio amplifier that requires adequate power
supply decoupling to ensure the output THD and
PSRR as low as possible. Power supply
decoupling affects 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 is good, placing it as close as possible to
the device VDD terminal. For filtering lower-
frequency noise signals, a capacitor of 10µF or
larger, closely located to near the audio power
amplifier is recommended.
Shutdown Operation
In order to reduce shutdown power consumption,
the PAM8302A contains shutdown circuitry for
turn off the amplifier. This shutdown feature turns
the amplifier off when a logic low is applied on the
SD pin. By switching the shutdown pin over to
GND, the PAM8302A supply current draw will be
minimized in idle mode.
For the best power on/off pop performance,
the amplifier should be set in the shutdown
mode prior to power on/off operation.
Under Voltage Lock-out (UVLO)
The PAM8302A incorporates circuitry to detect
low on or off voltage. When the supply voltage
drops to 2.1V or below, the PAM8302A goes into a
state of shutdown, and the device comes out of its
shutdown state and starts to normal operation by
reset the power supply or SD pin.
Power Analog Microelectronics,Inc
www.poweranalog.com
9
09/2011 Rev1.5