FAN7031 Datasheet, PDF (16/20 Pages) Fairchild Semiconductor – 2W Stereo Power Amplifier with Four Selectable Gain Setting and Headphone Drive

FAN7031
Functional Description
The FAN7031 is a stereo 2W amplifier capable of delivering 1.85W continuous RMS power into a 4-ohm load. This
device has less than 0.75% THD+N across the entire frequency range at an output power of 1W. A thermally
enhanced TSSOP package is used to allow for maximum dissipation of package heat.
Gain selection is achieved by driving G0 and G1 inputs according to the table below.
G0
G1
SE/BTL
AV
Zin
0
0
0
6dB
90kΩ
0
1
0
10.3dB
55kΩ
1
0
0
15.6dB
30kΩ
1
1
0
21.6dB
15kΩ
X
X
1
4.3dB
55kΩ
Gain select pins are activated only when SE/BTL pin is set to low level. If SE/BTL pin is high, the amplifier configu-
ration is changed as SE(single-ended) mode and the gain of SE amplifier is fixed to 4.3dB (about 1.64).
Gain is varied by changing the taps on input resistors, and such change in gain will cause variation in the input
impedance. Input impedance (Zin) is described in the above table. The impedance variation determines amplifier
lowest bandwidth. Thus, input DC decoupling capacitors must be carefully selected.
Applications Information
PCB Layout and Supply Regulation
Metal trace resistance between the BTL output and the parasitic resistance of the power supply line both heavily
affect the output power. In order to obtain the maximum power depicted in the performance characteristics figures,
outputs, power and ground lines need wide metal trace. The parasitic resistance of the power line increases ripple
noise and degrades the THD and PSRR performance. To reduce such unwanted effect, large capacitor must be
connected between VDD pin and GND pin as close as possible. To improve power supply regulation performance,
use a low ESR capacitor.
Power Supply Bypassing
Selection of proper power supply bypassing capacitor is critical to obtaining lower noise as well as higher power
supply rejection. Larger capacitors may help to increase immunity to the supply noise. However, considering eco-
nomical design, attaching 10µF electrolytic capacitor or tantalum capacitor with 0.1µF ceramic capacitor as close
as possible to the VDD pins are enough to get a good supply noise rejection.
Selection of Input Capacitor
Input capacitor blocks DC signal also low frequency input signal. Thus, this capacitor acts as a high pass filter. The
-3dB frequency of this filter is determined by input capacitor and input impedance of the amplifier. The frequency is
f_–3dB = -₂---_π-----_â‹---_Z-¹---_i--_n----_â‹----_C--
As shown previously, the input impedance is changed by selecting gain. Considering smallest Zin (=15kW), the
capacitance which meets f-3dB frequency of 20Hz is 0.53uF. Thus, selecting the capacitance higher than 0.53uF,
the lowest frequency of audio signal can be amplified without gain loss.
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