Diodes PAM8302A - Manual (Page 7)

PAM8302A
Document number: DSxxxxx Rev. 2 - 5
7 of 14
www.diodes.com
April 2013
© Diodes Incorporated
PAM8302A
A Product Line of
Diodes Incorporated
Application Information
Test Setup for Performance Testing
PAM8302A DUT
Notes: 1. The AP AUX-0025 low pass filter is necessary for every class-D amplifier measurement with AP analyzer.
2. Two 22μH inductors are used in series with load resistor to emulate the small speaker for efficiency measurement.
Maximum Gain
As shown in block diagram (Page 2), the PAM8302A has two internal amplifier stages. The first stage's gain is externally con figurable, while the
second stage's is internally fixed. The closedloop gain of the first stage is set by selecting the ratio of RF to RI while the second stage's gain is
fixed at 2x.The output of amplifier one serves as the input to amplifier two, thus the two amplifiers produce signals identical in magnitude, but
different in phase by 180°. Consequently, the differential gain for the IC is
A =20*log [2*(R
F
/R
I
)]
The PAM8302A sets maximum R =80kΩ, minimum R
I
=10kΩ, so the maximum closed-gain is 24dB.
Input Capacitor (C
I
)
Intypical application, an input capacitor, C
I
is required to allow the amplifier to bias input signals to a proper DC level for optimum operation. In
this case, C
I
and the minimum input impedance R
I
(10k internal) form a high pass filter with a corner frequeny determind by the following
equation:
C R 2
1
f
I I
C 

It is important to choose the value of C
I
as it directly affects low frequency performance of the circuit, for example, when an application requires a
flat bass response as loas as 100Hz,. Equation is reconfigured as follows:
f R 2
1
C
I I
I 

As the input reisitance is varible, for the C
I
value of 0.16µF, one should actually choose the C
I
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 (R
I
, R
F
, C
I
) 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 capacitior is used, the positive side of the capacitor should face the
amplifier input in most applications as the DC level is held at V
DD
/2, which is likely higher than the source DC level. Please note that it is
important to confirm the capacitor polarity in the application.