Mobile phones and other portable electronic products are integrating more and more multimedia functions, which has aroused great interest in adding stereo functions. This article introduces a low-cost stereo switching solution based on the MS6335 + MS6863 chip combination of Maosheng, which is very suitable for MP3 players, portable media players (PMP), mobile phones, portable TVs, portable DVDs and other products.
Currently, portable devices such as 3G mobile phones or portable multimedia players can easily provide audio 3D effects through digital processing. With this device, stereo headphones can be embedded to listen, so that the left and right signals can be obtained from the DAC or FM radio. Although the headphone power is about 10mW on a 32-ohm load, the main speaker can be easily used to generate and output up to 1W of power for an 8-ohm load. Due to the need to provide a stereo solution rather than a traditional mono system, it is difficult to provide highly efficient cleaned audio signals at these power levels.
Taiwan ’s MOSA Electronics Corp. ’s MS6335 digital / analog converter works with the MS6863 low-distortion power amplifier. It can be used for MP3 players, portable media players (PMP), mobile phones, portable TVs, and Portable products such as portable DVDs provide a complete low-cost stereo switching solution. The functional diagram is shown in Figure 1.
Figure 1. Functional diagram of a low-cost stereo switching solution based on MS6335 + MS6863
MS6335 digital / analog converter
MS6335 is a 16-bit digital / analog converter (DAC) that integrates a Class AB stereo headphone driver, with an I2C SPI interface, and also has a volume control function. Its internal structure is shown in Figure 2. Its unique synchronous decoding technology combined with precisely matched initial modulation current source effectively eliminates zero-crossing distortion to produce high-quality audio.
Figure 2. The internal structure of MS6335
The MS6335 is produced using a CMOS process. The volume control range is 6dB to -39dB (1.5dB / step). The output voltage can be adjusted by an external resistor. It has excellent power supply rejection ratio (PSRR) and can reproduce high-quality audio. Ideal for low power, small form factor portable applications. Typical application of MS6335 in MP3 player with FM function. See Figure 3.
Figure 3. Application of MS6335 in MP3 player with FM function
Figure 4. The internal structure of MS6863
MS6863 low distortion power amplifier
The MS6863 is a low-distortion power amplifier capable of driving dual 4-ohm BTL loads with a continuous average power of 2 & TImes; 2W, or stereo 32-ohm single-ended (SE) headphones with 2 & TImes; 90mW. Through the earphone detection pin, MS6863 can automatically switch between dual BTL and stereo SE mode. In most applications, this BTL configuration can eliminate coupling capacitors at the output, making the design simpler and cost-effective. MS6863 adopts TSSOP20 package, its gain can also be set by external resistor, there is no POP noise when shutting down, its typical application circuit is shown in Figure 5.
Figure 5. Typical application circuit of noise-free shutdown of MS6863
Scheme description
This design is composed of MS6335 audio DAC and MS6863 power amplifier, with stereo digital and analog signal input terminals and stereo Line-Out, speakers and headphones three output terminals. The demo board can switch the sound source and output, and can be used as a volume control.
Fig. 6, the demo board composed of MS6335 audio DAC and MS6863 power amplifier
This design uses infrared and MCU as the control, MCU maintains the Standby state, MS6335 and MS6863 initial state is Power down mode. The stereo digital signal source comes from a digital signal processor (MP3 decoder, set-top box) and can be selected in I2S or Normal format. The stereo analog signal comes from FM and other signals. The stereo output can be connected to 32 ohm or 16 ohm headphones, which can directly drive 8 ohm or 4 ohm stereo speakers; Line-out has no driving capability, and a post-amplifier with driving capability is required.
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