PAM8902 Datasheet, PDF (8/13 Pages) Power Analog Micoelectronics – 30-Vpp Mono Class-D Audio Amplifier for Piezo/Ceramic Speakers

PAM8902
30-Vpp Mono Class-D Audio Amplifier for Piezo/Ceramic Speakers
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:
Vset pin configuration
Connect to AVDD
Floati ng
Connect to GND
Min
AVDD - 0.5V
1V
GND
M ax
AVDD
AVDD - 1V
0.5V
PVCC Voltage
17.5V
12V
8V
Audio amplifier maximum output voltage
11Vrms (Vpp=31.1V)
8Vrms(Vpp=22.6V)
5Vrms(Vpp=14.1V)
Input Resistance (Ri)
The input resistors (Ri=Rin+Rex) set the gain of the amplifier according to Equation 1 when anti-saturation
is inactive.
G=20 Log [12.8*Rf/(Rin+Rex)] (dB)
Gs et
Gs et=Vdd
Gse t=Floati ng
Gset=GND
Rin
77.4kΩ
100kΩ
122.6kΩ
Rfb
122.6kΩ
100kΩ
77.4kΩ
Where Rin is a 77.4KΩ internal resistor, Rex is the external input resistor,Rf is a 122.6K Ω 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.
Input Capacitors (Ci )
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:
fc
=
1
2pRiCi
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 150kΩ and the specification calls for a flat bass response are down to 150Hz.
Equation is reconfigured as followed:
Ci = ¹
2pRifc
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 / _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.
Decoupling Capacitor
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
Power Analog Microelectronics, Inc
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01/2012 Rev1.4