PAM8301 datasheet(8/11 Pages) PAM

8 / 11 page

09/2008 Rev 1.2

Power Analog Microelectronics Inc

Application Information

www.poweranalog.com

PAM8301

Filterless Class-D Mono Audio Amplifier

Maximum Gain

As shown in block diagram (page 2), the PAM8301

has two internal amplifier stages. The first stage's

gain is externally con figurable, while the second

stage's is internally fixed. 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 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 =20*log [2*(R /R )]

The PAM8301 sets maximum R =80k , minimum

R =10k , so the maximum closed-gain is 24dB.

Input Capacitors (Ci)

Power Supply Decoupling (Cs)

Shutdown Operation

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)

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:

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:

As the input resistance is variable, for the Ci value

of 0.16 F, one should actually

choose the Ci

within the range of 0.1 F to 0.22 F. 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.

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 r esponse. 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.

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.

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

pin.

μμ

()

2RiCi

()

2R f

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