Have you ever dreamed of doing something awesome but psyched yourself out, thinking that it was going to be too hard to complete? Then, after you finally got the courage to go for it, you looked back in astonishment – it was really fairly easy.
This is the scenario I’m witnessing lately when speaking with automotive audio design engineers about switching their car radio solution from a traditional Class-AB amplifier to a Class-D amplifier. So let’s talk about the two primary concerns that I hear about most often: the impact on printed circuit board (PCB) size and potential electromagnetic interference (EMI) concerns.
Concern No. 1: Class-D amplifiers are going to enlarge your PCB footprint
Typical Class-D audio amplifiers switch the amplifier on and off at ~400 kHz and require the use of 8.2-µH or 10-µH inductors for proper audio performance.
TI’s TPA6304-Q1 Class-D amplifier switches at a 2.1-MHz switching frequency. It’s reduced ripple current means that it can take advantage of much smaller and lighter-weight 3.3-µH inductors, as shown in Figure 1.
Figure 1: Comparison of inductor size vs. switching frequency
The TPA6304-Q1 is designed with TI’s latest mixed-signal manufacturing technology, which when coupled with the use of 3.3-µH Inductors shrinks the overall size of the complete four-channel amplifier solution (including all required passive components) to 272 mm2, as shown in Figure 2.
Figure 2: The TPA6304-Q1 four-channel Class-D amplifier
To put this into perspective, Figure 3 shows that the complete TPA6304-Q1 solution is smaller than a traditional Class-AB amplifier by itself.
Figure 3: TPA6304-Q1 Class-D amplifier solution size compared to a Class-AB amplifier
Concern No. 2: Class-D amplifiers introduce EMC issues
By nature, a Class-D audio amplifier switches its output on and off during each cycle of the clock, whereas a Class-AB amplifier does not switch. This does not imply, however, that a Class-D amplifier will introduce unmanageable electromagnetic compatibility (EMC) issues.
I’d like to specifically review several ways that the TPA6304-Q1’s amplifier design helps alleviate EMC concerns:
Figure 4: Typical 400-kHz Class-D amplifier harmonics
Figure 5: The TPA6304-Q1’s high switching frequency above the AM band
In case some PCB layout designs introduce EMI challenges, the TPA6304-Q1 has implemented a Kilby Labs-developed, proprietary spread-spectrum technique. Figure 6 illustrates how this feature helps spread out a narrowband energy source across a much larger frequency band, thereby reducing the peak energy.
Figure 6: Spread-spectrum technology background
The TPA6304-Q1 2.1-MHz higher-switching-frequency automotive Class-D audio amplifier fulfills industry demands for next-generation car radios and external amplifiers. In addition to reducing the thermal load in systems, the amplifier’s design addresses concerns about PCB size and EMC when transitioning from Class-AB amplifiers to Class-D amplifiers.
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