2.3.4 Chime Audio Amplifier

The audio chime is used for safety warnings and turning indications. The TPA6211T-Q1 device is a simple and easy-to-design fully-differential audio power amplifier that can be used with 8-Ω or 4-Ω speakers. The TPA6211T-Q1 is configured for a single-ended input in this design. A PWM signal or a 1-kHz square wave generated from a digital output is low-pass filtered with components R74 and C71 to approximate a sine wave. In this reference design, the gain is currently set to 3.2 V/V. Remember that when changing the gain, the TPA6211 input capacitors (C70 and C72) form a high-pass filter with the input resistors (R73 and R75). The feedback resistors are internal to the TPA6211T-Q1 and trimmed to 40 kΩ. In this design, the audio chime warning is produced by a MSP430 PWM signal. By passing the PWM signal through a low-pass filter, the system produces the chime warning when the signal light is turned on or when a general warning notification occurs.