TS4962M Product Page
The growth in battery-operated media-enabled consumer
devices has exploded in the last few years. For these
consumer products, high quality sound capabilities, coupled
with very low power consumption is critical. Class D audio
amplifiers, such as ST’s new TS4962M, offer the
highest efficiency, at a competitive price and are therefore
absolutely key for new mobile applications.
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The TS4962M is a Class D, 3W mono audio amplifier used for
driving external speakers. It is perfect for use in mobile phones,
portable DVD players, PDAs, PCs and peripherals. For these applications,
sound quality must be tempered by low power consumption, as
every device in the signal chain must be as power-efficient
as possible to achieve a long battery life.
The TS4962M offers some serious advantages compared to class
AB audio amplifiers. First among these is a very high efficiency
rating of up to 90%. This translates simply into a much more
powerful audio signal for the same power consumption used for
an equivalent class AB circuit, or conversely, much lower power
consumption for a given audio volume. Class D topology also
offers a simplified, filter-free circuit design, leading to
a lower total component count for a given application.
The TS4962M, like almost all of ST’s audio amplifiers
for mobile applications, is available in a Flip-Chip package
(and soon to be available in DFN8), which greatly reduces the
board space required.
Typical internal circuit topology
| Class D = High Efficiency |
Class D audio amplifiers can offer greatly increased efficiency,
as compared to Class AB amplifiers, because of their circuit
topology.
Similar in scheme to a switching regulator, a Class D amplifier
pulse-width-modulates the audio-input signal with a higher frequency
square wave so that audio-signal information becomes the variations
in pulse width of this modulated signal. The frequency of the
PWM oscillator is important as it determines both the output-filter
requirements and the sampling rate for the audio input. In the
TS4962M the best balance between performance and component size
is achieved with an oscillator frequency that is at least 10
times the maximum signal frequency (which is typically 20kHz).
The theoretical best efficiency for a traditional Class AB linear-amplifier
output stage is 78%, but linear amplifiers exhibit this efficiency
only at their peak output power.
Efficiency versus output power
On the other hand, the output stage of a Class D amplifier,
because it uses a pulse-modulated signal to transport the audio
signal, can be amplified with very low distortion (under 1%
THD) and with theoretically limitless gain. The speakers themselves
provide low-pass filtering necessary to remove the PWM frequency
of the signal, leaving just a pure, amplified audio signal.
This means that Class D amplifiers are not only more efficient
in terms of gain per power consumption, but also eliminate the
need for an additional filtering, thereby reducing total component
count.
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