Diodes PAM8301 - Manual (Page 7)

PAM8301
Document number: DSxxxxx Rev. 1 - 3
7 of 10
www.diodes.com
July 2013
© Diodes Incorporated
PAM8301
A Product Line of
Diodes Incorporated
Application Information
(cont.)
Maximum Gain
As shown in block diagram (Page 2), the PAM8301 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 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
VD
= 20*log [2*(R
F
/R
I
)]
The PAM8301 sets maximum R F = 80k Ω, minimum R
I = 10k Ω, so the maximum closed-gain is 24dB.
Input Capacitors (C
I
)
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:
C R 2
1
f
I I
C 

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:
f R 2
1
C
I I
I 

As the input resistance is variable, 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 capacitor 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.
Power Supply Decoupling (C
S
)
The PAM8301 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 1.0 μF is good, placing it as close as possible to the device V
DD
terminal. For filtering lower-frequency noise signals, a capacitor of 10 μF or larger, closely located to near the audio power amplifier is
recommended.
Shutdown Operation
In order to reduce shutdown power consumption, the PAM8301 contains shutdown circuitry for turn off the amplifier. This shutdown feature turns
the amplifier off when a logic low is applied on the SHDOWN pin. By switching the shutdown pin over to GND, the PAM8301 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 PAM8301 incorporates circuitry to detect low on or off voltage. When the supply voltage drops to 2.1V or below, the PAM8301 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.