Introduction

If you already know about class A, B, and AB, they are all linear amplifiers with constant gain where the audio is fed to the base of a transistor. The latest class D audio amplifier is switch type amplifier by using Pulse Width Modulator (PWM) amplifier. In class A, B and AB type amplifiers which are linear amplifiers, the gain is constant irrespective of bus voltage variations but the gain is proportional in class D amplifiers. Class D amplifiers are much efficient than linear amplifiers.
The lower power consumption of Class D amplifiers make them suitable for audio amplifier design. Class D is more relevent for battery operated devices such as phones and notebooks, netbooks and tablets due to low power consumption.

Class D amplifier market: Due to the power performance of Class D amplifiers, its market is growing around 20- 30% on average.

Drawback: The drawback of class D amp is, switching of the outputs in the Class D amplifiers causes EMI and hence in most applications which require EMI certification need to be dealt cautiously.

Class D amplifiers are used in designing audio amplifiers in many applications, including powered subwoofers, powered speakers, mobile applications (to save battery power), and bass amplifiers.

Here below we provide a list of class D amplifiers from leading semicoductor vendors.

Parts selection table from key vendors of anlog ICs

Suggestion on some specific ICs:

Maxim's MAX98314 is a 3.2W class D amplifier integrated with input coupling capacitors built by using the 3D chip assembly.

NXP's TFA9881 and TFA9882 are the smallest digital-in mono class D audio amplifier which delivers up to 3.4W of power with power consumption of 6.5mW.

NXP offers class-D amplifiers with a range from 0.4W to 200W in both analogue and digital inputs. NXP also offers class D car radio amplifiers that deliver up to 2 x 135 W in to 4 ohm loads.

On Semi's NCS8353 stereo audio amplifier can deliver continuous output power up to 20 W per channel in to an 8 ohm bridge tied load(BTL) can be suitable for flat panel TVs.

ST Micro's TDA7498E dual-BTL class D amplifier exhibits unparalleled power density of 3.2W/mm2.

· Texas Instriment's TPA3116D2, TPA3118D2, TPA3130D2 and TPA3131D2 are medium-power, analog-input Class-D speaker amplifiers while TPA2011D1/37D1/39D1 and TPA2015D1 are low-power, analog-input, Class-D speaker amplifiers.

International Rectifier's class D driver + digital audio MOSFETs such as IRS4301(1 channel), IRS2052(2 channels), IRS2053(3 channels), IRS2093(4 channels), etc., provide output power from few tens of Watts up to 500 W. IR also provides Integrated class D audio amplifiers in trade name called PowlRaudio, such as IR4301, IR4311, IR4302, etc.,

National's LM48901 is a quad class D amplifier (spatial array) configured through an I2C compatible interface with superior click and pop suppression.

Texas Instruments made LM48901 quad Class D spatial array employ distributed sound processing coupled with loudspeaker array technology to produce an immersive audio experience for space-constrained applications.

Texas Instruments' LM49251's Class G headphone amp dynamically reduces the supply voltage to lower power consumption and extend audio (MP3, movies, etc.) playback time. The loudspeaker's ALC provides designers with several options to control audio distortion levels and prevent speaker damage.|

Maxim's MAX98304 is the smallest Class D amplifier at 1mm x 1mm. This amplifier increases output power by 23% to 3.2W and reduces noise by 39% to 19µVRMS, as compared to Maxim's previous-generation device.

The MAX98400 from Maxim is filterless Class D amplifiers available in 2 x 12W, 2 x 20W, and 1 x 40W configurations. The MAX98400 amplifiers ideal for TVs, notebooks, and all-in-one desktop applications.

MAX98300/MAX98302 from Maxim are mono/stereo 2.4W/channel Class D amplifiers which do not need EMI-suppression components. The MAX98300/MAX98302 consume supply current of 700µA/channel. Maxim's MAX98500, is a boosted 2.2W Class D amplifier designed for battery-operated portable devices. This device integrates a boost converter to provide a constant output power and, therefore, louder audio output over a wide range of battery supply voltages.

The TS4999 from STMicroelectronics is a two-channel, 2.8W class D stereo audio amplifier IC featuring 3D audio effects that improves sound quality from portable equipment.

ST's TDA7498 is suggested for equipments such as DVD and Blu-ray players, home theater, active speakers, and docking stations.

Texas Instruments suggests its TPA2015D1 allows more than twice the battery life compared to the nearest competing amplifier and is available in a compact 2-mm x 2-mm WCSP package for space-constrained applications including smart phones, notebooks, portable navigation devices, portable docking station and portable DVD players. In addition, the amplifier incorporates battery monitoring automatic gain control (AGC) and SpeakerGuard technology.

The TPA2028D1 and TPA2026D2 from TI incorporate DRC to boost soft volumes automatically, allowing designers to compress the dynamic range of the audio to match the dynamic range of the speaker.

MAX97000/MAX97001*/MAX97002 feature Class D mono speaker amplifier with distortion limiter; a DirectDrive II Class H stereo headphone amplifier; and an ultra-low-noise, analog bypass switch.

WM9081 from Wolfson packs DAC and class D amplifier in single chip.

The SSM2517 Class D audio amplifier from Analog devices also combines on a single chip an audio DAC (digital-to-analog converter), power amplifier, and a PDM digital interface.

A new LM4675 mono, 2.65W, Class D Boomer audio amplifier from Texas Instruments reduces electromagnetic interference (EMI) more than 11 dB below the United States Federal Communications Commission (FCC) limit to lower system noise in portable devices including cell phones, smart phones, music players, notebook computers, DVD players, gaming devices and other portable electronics.

The TAS5414 and TAS5424 Class D amplifiers from TI introduce the power efficiency of digital amplification for automotive audio applications, such as head units and external amplifiers.

MAX9708 from Maxim is a Class D amplifier optimized for flat-panel display applications including LCD and PDP televisions and home audio equipment. This is a filterless amplifier that requires very few external components.

For learning audio amplifier design and for circuit ideas using class D amp visit below sites:

1. classdtutorial

2. sloa031

3. E-project-041808-145643

4. UM10155

5. class_d

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