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Design Features
Energy Efficiency with Class D Amplifier Modules
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IR’s reference design, IRAUDAMP5, uses the IRS2092 driving two IRF6645 DirectFET® audio MOSFETs to create a 120W two-channel amplifier with half-bridge output, using 60% less board space and around 20% fewer parts than a comparable design built with discrete components. The reference design guides important aspects such as designing the output low-pass filter and feedback loop, programming deadtime, selecting external current and temperature sensing components, and optimising board layout.
Benefiting from the high functionality of the IRS2092 and the high audio performance of the optimised output MOSFETs, the reference design achieves very low THD+N of 0.005% at the output when driving 2x60W into 4Ω speaker loads.
Figure 1 shows a simplified block diagram of this reference design, illustrating the key functional elements of a class-D amplifier and highlighting how a module such as the IRS2092 greatly simplifies circuit design.
Figure 1: Block diagram of IRAUDAMP5 Class-D amplifier reference design.
Complete Class-D in a Module
Taking this modular concept a step further by building-in optimised power MOSFETs alongside the error amplifier, PWM controller gate driver and protection circuitry within the same package, IR’s latest PowIRaudio™ IR43xx integrated power modules enable a further reduction in component count allowing board-space savings of up to 70%.
The PowIRaudio family comprises four devices supporting full-bridge and half-bridge topologies from 35W/4? to 130W/4?. Using these devices, designers can configure 2.1-channel, 5-channel, 6-channel or 7.1-channel applications. The devices have a wide operating voltage range, up to 62V/±31V for the IR4301/4302 or 32V/±16V for the IR4311/4312. Other key features common to the family include over-current protection, thermal shutdown, internal/external shutdown and floating differential input. The IR4302 and IR4312 also offer clip detection.
Using these devices designers can build amplifiers for typical music playback applications that do not require a mechanical heatsink and are capable of achieving outstanding audio performance figures such as THD+N as low as 0.02%. High noise immunity in the controller IC ensures reliable operation in a variety of environmental conditions. The devices are housed in thermally efficient PQFN packages measuring 5mm x 6mm for the IR4301/4311 and 7mm x 7mm for the IR4302/4312, thereby maximising the benefits of IR’s advanced class-D co-packaged solution.
To provide a head-start for customers using these devices, IR has compiled six reference designs that include single-ended and split power supply configurations and provide audio output power ranging from 35W to 130W per channel with little or no heat-sinking required. Among these, the IRAUDAMP17 reference design for a 100W 2-channel heatsink-free amplifier using the IR4302, shown in figure 2, illustrates how the high efficiency of the class-D switching amplifier enables an extremely compact, yet high performing result.
Figure 2: Reference design for100W 2-channel class-D amplifier, using IR4302 featuring integrated output MOSFETs.
Conclusion
As the class-D amplifier becomes widely used in high-performing, miniaturised audio products, semiconductor vendors are taking responsibility for key aspects of the power electronics design by delivering purpose-built gate-driver modules incorporating key functional elements of a class-D amplifier. These modules have enabled a chipset approach to class-D design, using discrete output transistors. The latest generation of modules that also incorporate the audio output MOSFETs in the same package now enable even smaller new products to be delivered to the market at competitive prices.
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