Audio power amplifier IC and audio system provided with the same

An audio system comprising a first audio power amplifier IC and a second audio power amplifier IC,

• said first audio power amplifier IC and said second audio power amplifier IC each including
• a clock generation circuit generating an internal clock,
• a clock terminal for outputting said internal clock or receiving an external clock,
• a clock selection circuit selecting said internal clock or said external clock as a reference clock,
• a first audio signal input terminal for receiving a first audio signal,
• a first digital power amplifier circuit performing pulse modulation on said first audio signal based on said reference clock to output a pulse synchronized with said reference clock,
• a second audio signal input terminal for receiving a second audio signal,
• an inversion circuit inverting said first audio signal and outputting the resultant audio signal,
• an audio signal selection circuit selecting and outputting the audio signal output from said inversion circuit or said second audio signal, and
• a second digital power amplifier circuit performing pulse modulation on said selected audio signal based on said reference clock to output a pulse synchronized with said reference clock, wherein
• said clock selection circuit selects said external clock as said reference clock in a case where said audio signal selection circuit selects the audio signal output from said inversion circuit,
• in said audio system,
• said clock terminals respectively of said first audio power amplifier IC and said second audio power amplifier IC are connected to each other,
• in said first audio power amplifier IC, said clock selection circuit selects said internal clock as said reference clock and outputs said internal clock from said clock terminal, and
• in said second audio power amplifier IC, said clock selection circuit selects the external clock as said reference clock received from said first audio power amplifier IC via said clock terminal.