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User manual for MA120xxx reference boards
Schematic, layout and design considerations
2.2
Design considerations
The RFB is elegant because of its small form factor, while still being able to operate at up to 80 W output power
per channel. This is possible due to the multi-level technology of the MA12070 and MA12070P devices.
Thermal considerations:
o Power-efficient operation allows heatsink-free operation because the bottom layer of the PCB
design (connected to the heatsink pad of the IC) is sufficient for cool operating conditions. This
holds when considering playback of real audio signals.
o Figure 5 and Figure 6 show the top and bottom PCB design respectively. It can be seen that all the
component placement and main routing is done on the top layer.
o It is important to have as little routing as possible on the bottom layer since it needs to be
optimized for thermal heat flow.
o Routing done on the bottom layer is chosen in such a way that it still allows for good thermal heat
flow. In this way, the complete bottom plate can function as a heatsink for the amplifier IC.
o Vias placed between bottom and top ground planes add to the copper mass that functions as a
heatsink.
Filterless operation:
o Multi-level technology also significantly reduces out-of-band noise, which allows LC filter-free
operation. Only a small, SMD-sized EMI filter is needed.
o Figure 1 shows the footprint and PCB size it takes. The board size is significantly reduced due to a
small-sized EMI filter compared to a bulky LC filter.
o The use of an LC filter is also not needed to optimize the efficiency of the amplifier. The speaker's
inductive behavior is sufficient for efficient operation of the amplifier. This is again enabled by
reduced out-of-band noise of the amplifier.
Buck regulator:
o A buck regulator (TPS62175) has been included in the design to derive a 5 V rail from the PVDD input
rail. 5 V is needed as the core supply voltage for the MA120xx(P). TPS62175 has been chosen to
balance the need for cost, efficiency and size. The current design of the buck regulator generates 5
V from 26 V PVDD with approximately 85 percent efficiency. Efficiency could have been increased by
increasing the inductance, which would have increased the footprint; Infineon opted for a smaller
footprint instead.
Application Note
12 of 28
V 1.0
2019-04-28
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