Datasheet LA4558 (Sanyo) - 4

LA4558 Application Circuits
Voltage gain adjust · Stereo mode The voltage gain is determined by on-chip resistor R1 (R2) and external feedback resistor RNF as follows : R1 VG=20 log [dB] RNF+R2 Any voltage gain can be obtained by external resistor RNf. · Bridge amplifier mode The CH1 is a noninverting amplifer and the CH2 is an inverting amplifier. The total voltage gain, being apparently higher than that of the CH1 by 6dB, is approximately calculated by the following formura. VG=20log R2/R1+6 (dB) To reduce the voltage gain, Rf is connected and the following formura is used. VG=20log R2/Rf=R1+6 (dB) Proper cares in using LA4558-applied set 1. Slider contact noise of variable resistor Since the input circuit uses PNP transistors, no input coupling capacitor is required. However, if slider contact noise of the variable resistor presents any problem, connect a capacitor in series with input. 2. Pop noise If pop noise generated at the time of power ON/OFF disturbs you, connect a resistor of 500Ω to 1kΩ across the middle point and GND. Thermal Design Since the DIP-12F package is such that the Cu-foiled area of the printed circuit board is used to dissipate heat, make the Cu-foiled area in the vicinity of the heat sink of the IC as large as possible when designing the printed circuit board. Power dissipation Pd is increased depending on the supply voltage and load. So, it is recommended to use the printed circuit board together with the heat sink. The following is a formula to be used to calculate Pd (for stereo use). For AC power supply, however, it is recommended to actually measure Pd on the transformer of each set. For bridge amplifier use, Pd is calculated at 1/2 of the load. No.2088–4/9