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Victor Ceron

Jan 14, 2016

Mid/High-Power
Class-D Amplifiers

TAS5404-Q1

audioportal

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Related

The head unit: understanding car audio amplifier system demands
– part 1

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Cars of all sizes and price ranges are delivering a growing
array of entertainment and information to enhance the driving and riding
experience. Today’s factory-installed head units typically combine
entertainment, multimedia and driver information into one module; they offer
AM/FM and satellite radio, a CD/DVD player for music and video, a navigation
system, data and multimedia ports (USB, Bluetooth®, line in, line out,
video in), and general and vehicle status information.

The head unit is indeed the brain and centerpiece of the car’s
sound system. Modern head units are very complex automotive systems, integrating
high-speed processors and interface lines, very sensitive signal-chain blocks,
and high-output power audio and power supply components densely integrated in
the center of the dashboard.

Given such tight space restrictions, printed circuit board (PCB)
area and component count come at a very high premium in automotive head-unit
systems. It is imperative for automotive original equipment manufacturers (OEMs)
to consolidate functionality and minimize subsystem size to make room for
additional differentiation.

Audio in head units
Figure 1 is a very simplified
block diagram of a typical head-unit system.

Figure 1: Typical head unit simplified block
diagram (SBD)

In the figure, you’ll notice that:

The audio signal’s input front end and output are often combined into a
single CODEC, which comprises one or many analog-to-digital converters (ADCs)
and digital-to-analog converters (DACs).

If the audio processor or system on chip (SoC) has integrated DACs, you
may not need a codec, as the DAC section of the audio signal chain is
already integrated into the mixed-signal SoC.

The audio line level input from an external source is converted into
digital samples by the ADC and fed to the system’s audio processor or
SoC.

On the output side, DACs (whether integrated in the SoC or CODEC)
convert the digital audio signal from the processor to analog.

As the signal coming from the DAC has both low-voltage and low-current
capabilities, an audio amplifier is needed to provide the signal with the
required higher voltage and current capabilities to drive the drivers in the
speaker system.

Audio amplifiers: Class-AB vs. Class-D
Automotive
system designers have basically two alternatives when selecting the best audio
amplifier for their automotive head-unit systems: Class-AB or Class-D.

Class-AB audio amplifiers are today’s standard in automotive
audio. They are linear amplifiers that generate no electromagnetic interference
(EMI) and do not require many external electronic components. They are highly
inefficient, however, and require substantial passive or even active thermal
management in the form of heat sinks and fans.

On the other hand, Class-D audio amplifiers are highly efficient
switching amplifiers that need very little thermal management; however, they do
require output inductors that are not exempt from EMI concerns.

Class-D audio amplifiers are rapidly gaining in popularity as
their advantages over Class-AB become more evident and their total system cost
approaches parity with Class-AB systems.

Efficiency: speaker channels.
As infotainment systems
become more sophisticated, car manufacturers have increased their speaker
channel count to improve system differentiation and market appeal. The power
demands on the head-unit audio amplifier increase with the number of speaker
channels needed, but space and heat dissipation restrictions limit the power
dissipation in the head unit to just a few watts.

In Class-AB-based head units, you can solve this problem by
adding an external audio-amplifier box or trunk amplifier, although it increases
system complexity and cost greatly.

The high efficiency of Class-D-based head units
makes it possible to match the power demands of high-channel-count systems
without an external audio amplifier. Their low-power dissipation enables
multi-IC implementation directly in the head unit, providing a more
cost-effective and simple solution.

Figure 2: Class-D Amplifier based head units
greatly simplify thermal management in head units.

TI’s automotive Class-D amplifiers’ high efficiency reduces heat
dissipation and total system cost by eliminating the use of fans and expensive
aluminum heat-sink panels; compared to Class-AB amplifiers, Class-D amplifiers
like TI TAS5404-Q1
enables higher channel count, subwoofer 2Ω load capability, and output power in
the head unit with no need for an external amplifier.

By leveraging reduced-sized, low-cost, automotive-grade
metal-alloy inductors, these Class-D amplifiers reach a very small solution
size, down to 10cm2, and allow may allow six or more channels in
space-constrained head-unit systems.

In part 2 of this blog series, I will discuss EMI. In the
meantime, log in to post a comment below and let me know about your challenges
with head-unit audio design and space constraints.

Additional resources

Check out the TI
Designs Highly Efficient and Compact 100W Automotive Amplifier Reference
Design with Boost Converter.

Download the “TAS5404-Q1EVM User’s Guide.”

Watch the “TAS5404-Q1
Low Cost, Full Featured Class D Audio Amp for Automotive Head Units”
video.

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