Audio power amplifier circuit composed of LM4835/4838

As shown in the figure, this is the audio power amplifier circuit of LM4835/4838. The stereo left channel audio signal is input from pin 9, and the stereo right channel audio signal is input from pin 7. After amplification by the internal amplifier and 32-level DC volume control, the left channel speaker is driven from the left output (pin 12) and the -left output (pin 14) in the form of bridge output. At the same time, the right channel speaker is driven from the right output (pin 25) and the -right output (pin 23) in the form of bridge output. The outputs of pins 14 and 23 are also added to the headphone jack. The 4-pin external volume control potentiometer is used to adjust the volume (32 levels). The gain Av=2RF/Ri of the differential bridge output structure. Pin 8 is a mono buzzer input, which can generate a buzzer signal from a computer or laptop to drive a small speaker. Pin 27 is a micro-power shutdown control terminal. When pin 27 is VDD, the amplifier bias circuit is turned off, and there is no output from the headphone and speaker.

LM4835/4838 has two working modes. When the mode control pin (pin 1) is 0V, it is mode 0, which is the "line output" mode, and the amplifier gain is 1; when pin 1 is VDD, it is mode 1, and the output volume is controlled by the external volume potentiometer on pin 4. Note that pin 1 cannot be left floating. Pin 5 is the squelch control terminal. When pin 5 is VDD, the headphones and speakers are squelched and have no output; when pin 5 is 0V, the headphones and speakers output normally. The selection of the input coupling capacitor value should take into account the input frequency response (-3dB bandwidth), that is, f-3dB=1/2πRINCI. RIN is the input resistance, and CI is the input coupling capacitor.