PAM8902

30-Vpp Mono Class-D Audio Amplifier for Piezo/Ceramic Speakers

8

,

Power Analog Microelectronics Inc

www.poweranalog.com

01/2012 Rev1.4

Application Information

Select Boost Convertor Output Voltage

Customer can use Vset pin to set boost converor output voltage between 8V,12V and 17.5V.

Vset pin configuration table as below:

Input Resistance (Ri)

G=20 Log [12.8*Rf/(Rin+Rex)] (dB)

Input Capacitors (Ci )

Decoupling Capacitor

The input resistors (Ri=Rin+Rex) set the gain of the amplifier according to Equation 1 when anti-saturation

is inactive.

Where Rin is a 77.4K

internal resistor, Rex is the external input resistor,Rf is a 122.6K

internal resistor.

Resistor matching is very important in fully differential amplifiers. The balance of the output on the

reference voltage depends on matched ratios of the resistors. CMRR, PSRR, and cancellation of the

second harmonic distortion diminish if resistor mismatch occurs. Therefore, it is recommended to use 1%

tolerance resistors or better to keep the performance optimized. Matching is more important than ov erall

tolerance. Resistor arrays with 1% matching can be used with a tolerance greater than 1%.

Place the input resistors very close to the PAM8902 to limit noise injection on the high-impedance nodes.

For optimal performance the gain should be set to lower. Lower gain allows the PAM8902 to operate at its

best, and keeps a high voltage at the input making the inputs less susceptible to noise. In addition to these

features, higher value of Ri minimizes pop noise.

In the typical application, an input capacitor, Ci, is required to allow the amplifier to bias the input signal to

the proper DC level for optimum operation. In this case, Ci and the minimum input impedance Ri form is a

high-pass filter with the corner frequency determined in the follow equation:

It is important to consider the value of Ci as it directly affects the low frequency performance of the circuit.

For example, when Ri is 150k

and the specification calls for a flat bass response are down to 150Hz.

Equation is reconfigured as followed:

When input resistance variation is considered, the Ci is 7nF, so one would likely choose a value of 10nF. A

further consideration for this capacitor is the leakage path from the input source through the input network

(Ci, Ri + Rf) 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 applications. For this reason, a low-leakage tanta lum or

ceramic capacitor is the best choice. When polarized capacitors are used, the positive side of the capacitor

should face the amplifier input in most applications as the DC level is held at V /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 PAM8902 is a high-performance CMOS audio amplifier that requires adequate power supply

decoupling to ensure the output total harmonic distortion (THD) as low as possible.

The optimum decoupling is achieved by using two different types of capacitors that target on differ ent types

of noise on the power supply leads. For higher frequency transients, spikes, or digital hash on the line, a

Ω

Ω

Ω

DD

Vset pin configuration

Min

M ax

PVCC Voltage

Audio amplifier m axim um output voltage

Connect to AVDD

AVDD - 0.5V

AVDD

17.5V

11Vrm s (Vpp=31.1V)

Floating

1V

AVDD - 1V

12V

8Vrms(Vpp=22.6V)

Connect to GND

GND

0.5V

8V

5Vrms(Vpp=14.1V)

Gs et

Rin

Rfb

Gs et=Vdd

77.4k

Ω

122.6k

Ω

Gset=Floating

100k

Ω

100k

Ω

Gset=GND

122.6k

Ω

77.4k

Ω

Rifc

Ci

p

2

1

=

RiCi

fc

p

2

1

=