Plug and play Class D amplifiers to make wearable and iot audio easier
Date：January 28, 2025 Views：70
Abstract
Power-hungry displays are not the most efficient medium for connecting battery-powered portable, wearable, and iot devices. As a result, low-power audio is fast becoming a more popular alternative. In this design solution, this article reviews Class D digital audio amplifiers and discusses the limitations of some current solutions, then introduces a cleverly packaged IC that can quickly deliver high-quality audio for these applications with minimal configuration.
introduce
Digital Class D amplifier
Due to their high efficiency and excellent EM1 performance, filterless, digital input Class D amplifiers have become the accepted standard for driving speakers in consumer electronics devices. This is because they are not affected by the board design issues associated with their analog counterparts, especially signal integrity. Single-channel digital Class D amplifiers can be placed in remote locations on the board to minimize wiring for high-current battery and speaker load connections.
These amplifiers do not require the DAc and line drivers required for analog input Class D designs. As a result, space and system costs fall and designs become simpler. Many Class D amplifiers accept pulse code modulated PCM(or I 1s) data, which requires three wires: BCLK, LRCLK, and DIN (Figure 1). The PCM data format does not require up-sampling of data on the modulator or application processor to provide stereo data.
Simpler and smaller
The IC shown in Figure 2 addresses all aspects of these design problems and has the added advantage of being simpler and smaller, as well as a lower-power solution.
The amplifier offers several power advantages over other Class D amplifiers. It can operate with only one supply voltage (2.5V to 5.5V). It can accept input logic voltage levels as low as 1.2V (meaning that no level converter is required), but is robust enough to withstand input voltages up to 5.5V. It also operates at a high efficiency of 92%, reducing battery consumption.
Another beneficial feature is that if the DAIn pin remains low, the IC automatically goes into ultra-low power mode, where it consumes a tiny standby current of 1.5μA. This greatly reduces power consumption and is extremely beneficial in applications where there is no host GPIO available to control EN pins. However, it is important to note that the EN pin can be used to achieve an additional power-saving effect by placing the IC in the off mode, where it consumes only 15nA of current.
Conveniently, it also has a very fast 1ms startup time (four times faster than similar Class D amplifiers), which allows it to wait in ultra-low-power 1.5μA standby mode, even when connected to an LRA haptic driver.
Second, the part does not require additional Class D filtering to achieve the excellent EMI performance shown in Figure 5. Because it requires only one external bypass capacitor, the overall solution size is only 3.69mm2.
With audio interfaces rapidly becoming a common feature of battery-powered wearables, iot devices, and other types of small portable electronic devices, designers are looking for simpler and more cost-effective ways to add high-quality audio to their devices. In this design solution, we review the difficulties of integrating certain Class D amplifiers into space-constrained applications. We can conclude that the new flexible low-power digital input Class D audio amplifier generates "plug and play" simplicity for the task of integrating audio into any type of electronic device, making it ideal for portable devices, wearables, and iot devices. In addition to a 9-pin WLP package, the MAX98360 is also available in a 10-pin FC2QFN package.
Power-hungry displays are not the most efficient medium for connecting battery-powered portable, wearable, and iot devices. As a result, low-power audio is fast becoming a more popular alternative. In this design solution, this article reviews Class D digital audio amplifiers and discusses the limitations of some current solutions, then introduces a cleverly packaged IC that can quickly deliver high-quality audio for these applications with minimal configuration.
introduce
"Video Killed the Radio star" - The Buggles' hit record of o979 tells the story of the death of audio entertainment, when audio was delivered via a wireless AM/FM radio receiver (Figure 1), And video (in the form of television) is starting to take hold. Back then, the band couldn't have imagined that a portable electronic device would allow us to instantly stream any movie, or allow us to record our daily lives with near movie studio quality video. However, high-quality video is best appreciated when accompanied by equally high-quality audio, and it can be said that in the intervening years, the user's audio experience has been unforgivably neglected. Audio has become the "weak link" that enables countless complex functions on portable electronic devices such as wearables, AR/VR and compact iot products. Users have become accustomed to not having high expectations for audio from these devices. "After all, it's just a phone," is a mantra that's been repeated over and over and has become all too familiar.
Figure 1. Radio receiver
However, with the proliferation of wearables and iot devices, a welcome change is taking place. Users and designers are realizing that large, power-hungry screens are not suitable for battery-powered mobile devices. As a result, voice and audio are rapidly becoming the media of choice for controlling and receiving information from these devices. Users need a better audio experience than they currently have. Yes, it's easy for designers to blame the compact form factor of portable devices that limits speaker size. In many cases, however, it's not the speaker that causes poor audio quality, but the amplifier that drives it. In this design solution, we examine some of the difficulties of integrating and configuring digital Class D amplifiers in many portable electronic devices. We then demonstrated a miniature, low-power, Class D digital audio amplifier that can be seamlessly integrated to provide users with an unparalleled sensory experience, and in doing so justified the audio Renaissance that has become the medium of choice for interfaces to portable electronic devices.Digital Class D amplifier
Due to their high efficiency and excellent EM1 performance, filterless, digital input Class D amplifiers have become the accepted standard for driving speakers in consumer electronics devices. This is because they are not affected by the board design issues associated with their analog counterparts, especially signal integrity. Single-channel digital Class D amplifiers can be placed in remote locations on the board to minimize wiring for high-current battery and speaker load connections.
These amplifiers do not require the DAc and line drivers required for analog input Class D designs. As a result, space and system costs fall and designs become simpler. Many Class D amplifiers accept pulse code modulated PCM(or I 1s) data, which requires three wires: BCLK, LRCLK, and DIN (Figure 1). The PCM data format does not require up-sampling of data on the modulator or application processor to provide stereo data.
Figure 2. Input Class D using a three-wire PCM.
However, some traditional implementations of digital input amplifiers have some drawbacks. One of these limitations is the need for a separate, clean master clock (MCLK) to export a jitter free sampling clock. Other amplifiers offer adjustable sampling rates and/or bit depth, but this can require complex programming. In addition, most digital input amplifiers require two supply voltages - a low digital supply voltage (1.8V) and a high speaker supply voltage (2.5V to 5.5V). Another issue associated with their use is EMI. For high-quality audio applications, many Class D amplifiers require additional filtering to limit the impact of EMI, further increasing board size/cost. When choosing an amplifier to connect to a haptic driver, a fast connection time (less than a few milliseconds) is important, otherwise that part must remain permanently energized, causing the battery of a portable device to drain faster.Simpler and smaller
The IC shown in Figure 2 addresses all aspects of these design problems and has the added advantage of being simpler and smaller, as well as a lower-power solution.
Figure 3. MAX98360 digital Class D amplifier.
Unlike older Class D amplifiers, this IC uses an automatic sampling rate and bit depth configuration, eliminates the need for complex programming and provides a simple, effective "plug and play" audio solution. It has a flexible audio interface and supports 1s, left-justified and 8-channel time division multiplexing (TDM) data formats. It accepts 8kHz, 16kHz, 32kHz, 44.1kHz, 48kHz, 88.2kHz, and 96kHz sampling rates, and data can be 16, 24, or 32 bits in 1s and left-justified mode, and 16 or 32 bits in TDM mode. Its 10μV RMS output noise, 80dB PSRR and 110dB dynamic range specifications guarantee high-quality audio, which is particularly important for devices where speakers are close to the ear (such as AR/VR and wearables) and devices used in quiet environments (sleep AIDS)The amplifier offers several power advantages over other Class D amplifiers. It can operate with only one supply voltage (2.5V to 5.5V). It can accept input logic voltage levels as low as 1.2V (meaning that no level converter is required), but is robust enough to withstand input voltages up to 5.5V. It also operates at a high efficiency of 92%, reducing battery consumption.
Another beneficial feature is that if the DAIn pin remains low, the IC automatically goes into ultra-low power mode, where it consumes a tiny standby current of 1.5μA. This greatly reduces power consumption and is extremely beneficial in applications where there is no host GPIO available to control EN pins. However, it is important to note that the EN pin can be used to achieve an additional power-saving effect by placing the IC in the off mode, where it consumes only 15nA of current.
Conveniently, it also has a very fast 1ms startup time (four times faster than similar Class D amplifiers), which allows it to wait in ultra-low-power 1.5μA standby mode, even when connected to an LRA haptic driver.
Figure 4. Connect GAIN_SLOT to VDD or GND to get the desired gain Settings.
Table 1. I2S/ Left-justified gain Settings for the MAX98360.
Table 1. I2S/ Left-justified gain Settings for the MAX98360.
Figure 5. EMI performance using the 12-inch MAX98360. Ribbon line load.
Sum upWith audio interfaces rapidly becoming a common feature of battery-powered wearables, iot devices, and other types of small portable electronic devices, designers are looking for simpler and more cost-effective ways to add high-quality audio to their devices. In this design solution, we review the difficulties of integrating certain Class D amplifiers into space-constrained applications. We can conclude that the new flexible low-power digital input Class D audio amplifier generates "plug and play" simplicity for the task of integrating audio into any type of electronic device, making it ideal for portable devices, wearables, and iot devices. In addition to a 9-pin WLP package, the MAX98360 is also available in a 10-pin FC2QFN package.
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