Typical circuit diagram of LM4921 for two-channel headphone amplifier

The figure shows a typical circuit of the LM 4921 used in a two-channel headphone amplifier . The control line signals are input from the SPI interface bus J1: serial data signal SPI-DATA, serial enable signal SPI-ENABLE, and serial clock signal SPI-CLK. A full range of serial digital audio signals are input from the I2S interface bus J2: I2S data signal I2S-DATA, I2S clock signal I2S-CLK. I2S word selection signal I2S-WS (also known as Right/Left Select). The MCLK signal is input from P1: when S1 is disconnected, the external main clock MCLK input is selected; when S1 is short-circuited, the internal crystal oscillator (11.2896MHz) is selected. The stereo headphone output is output by J3, and a 100μF capacitor is used as a DC blocking capacitor to prevent the output DC current from damaging the headphones. The analog power supply and digital power supply of LM4921 are independent.

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