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Maxim’s MAX98400A/MAX98400B are high-performance, thermally efficient Class-D audio amplifiers. The MAX98400A can supply 2x20W to an 8-ohm load or 1x40W to a 4-ohm load, and the MAX98400B can supply 2x8W to an 8-ohm load. Single-supply 8V to 28V operation, Provides 67dB PSRR, 90% efficiency at 12V, and is mainly used in LCD/PDP TVs, LCD monitors, MP3 docking stations and notebook PCs. This article introduces the main features of the MAX98400A/MAX98400B, the MAX98400A/B functional block diagram, and the MAX98400A stereo and Mono configuration diagram, MAX98400 Class D audio amplifier reference design key features, circuit diagram, bill of materials, and PCB layout.

The MAX98400A/MAX98400B Class D amplifiers provide high-performance, thermally efficient amplifier solutions. The MAX98400A delivers 2x20W into 8I loads or 1x40W into a 4I load. The MAX98400B delivers 2x12W into 8I loads.

An integrated limiting circuit prevents output clipping distortion, protects small speakers from transient voltages, and reduces power dissipation.

A thermal-foldback feature can be enabled to automatically reduce the output power at above a junction temperature of +120NC. Traditional thermal protection is also available in addition to robust overcurrent protection.

The ICs operate from a single 8V to 28V supply and provide a high 67dB PSRR, eliminating the need for a regulated power supply. They offer up to 90% efficiency from a 12V supply.

Filterless modulation allows the ICs to pass EN55022B EMI limits with 1m cables using only a low-cost ferrite bead and small-value capacitor on each output. Both devices feature eight digitally controlled gain settings.

Comprehensive click-and-pop reduction circuitry minimizes noise coming into and out of shutdown.

The MAX98400A/MAX98400B are available in 36-pin and 24-pin TQFN packages, respectively, and are specified over the -40NC to +85NC temperature range.

MAX98400A/MAX98400B main features:

Wide 8V to 28V Supply Voltage Range

Single-Supply Operation

Low EMI: Active Emissions Limiting

Clipping Limiter

Low Quiescent Current

Thermal Foldback

Thermal and Overcurrent Protection

MAX98400A/MAX98400B applications:

LCD/PDP Televisions

LCD Monitors

MP3 Docking Stations

Notebook PCs

Figure 1. MAX98400A functional block diagram

Figure 2. MAX98400B functional block diagram

Figure 3. MAX98400A Stereo Configuration Diagram

Figure 4. MAX98400A Mono Configuration Diagram

MAX98400 Class-D Audio Amplifier Reference Design

This reference design demonstrates the use of the MAX98400 Class D audio amplifier in a stereo audio docking station application. The MAX98400 2.1 demo box is a complete powered speaker dock that uses two MAX98400 ICs to drive a 3-channel speaker system consisting of two 2in satellite speakers and one 5in subwoofer. The reference design is intended to be used with a portable audio player as its main music source. The overall solution size is very compact and features active equalization, powersupply monitoring, and dynamic equalization for the subwoofer.

Figure 5. MAX98400 Class-D Audio Amplifier Reference Design Outline

Key design features of the MAX98400 Class-D audio amplifier:

Compact all-in-one design

Operates from a single 12V to 20V DC power supply

High SPL output from a small box

High-efficiency Class-D design

Active EQ, including dynamic bass equalization

Excellent sound quality from cost-effective drivers

Figure 6. MAX98400 Class-D Audio Amplifier Reference Design Circuit Diagram(1)

Figure 7. MAX98400 Class D Audio Amplifier Reference Design Circuit Diagram(2)

Figure 8. MAX98400 Class D Audio Amplifier Reference Design Circuit Diagram(3)

Figure 9. MAX98400 Class D Audio Amplifier Reference Design Circuit Diagram(4)
Reference Design Materials List:

Figure 10. MAX98400 Class-D Audio Amplifier Reference Design PCB Layout
For details, see:
http://datasheets.maxim-ic.com/en/ds/MAX98400A-MAX98400B.pdf
and
http://pdfserv.maxim-ic.com/en/an/AN4320.pdf