TFA9892_SDS All information provided in this document is subject to legal disclaimers. © NXP B.V. 2017. All rights reserved.
Product short data sheet Rev. 1.0 — 1 September 2017 9 of 27
NXP Semiconductors
TFA9892
12 V boosted audio system with adaptive sound maximizer and
speaker protection
8. Functional description
The TFA9892 is a highly efficient mono Bridge Tied Load (BTL) class-D audio amplifier
with a sophisticated SpeakerBoost protection algorithm. Figure 1
is a block diagram of the
TFA9892.
A SpeakerBoost protection algorithm, running on a CoolFlux Digital Signal Processor
(DSP) core, maximizes the acoustical output of the speaker while limiting membrane
excursion and voice coil temperature to a safe level. The mechanical protection
implemented guarantees that speaker membrane excursion never exceeds its rated limit,
to an accuracy of 10 %. Thermal protection guarantees that the voice coil temperature
never exceeds its rated limit, to an accuracy of 10 C. Furthermore, advanced signal
processing ensures the audio quality remains acceptable at all times.
The protection algorithm implements an adaptive loudspeaker model that is used to
predict the extent of membrane excursion. The model is continuously updated to ensure
that the protection scheme remains effective even when speaker parameter values
change or the acoustic enclosure is modified.
Output sound pressure levels are boosted within given mechanical, thermal and quality
limits. An optional Bandwidth extension mode extends the low frequency response up to a
predefined limit before maximizing the output level. This mode is suitable for listening to
high quality music in quiet environments.
The frequency response of the TFA9892 can be modified via ten fully programmable
cascaded second-order biquad filters. The first two biquads are processed with 48-bit
double precision; biquads 3 to 10 are processed with 24-bit single precision.
At low battery voltage levels, the gain is automatically reduced to limit battery current. The
output volume can be controlled by the SpeakerBoost protection algorithm or by the host
application (external). In the latter case, the boost features of the SpeakerBoost protection
algorithm must be disabled to avoid neutralizing external volume control.
The SpeakerBoost protection algorithm output is converted into two pulse width
modulated (PWM) signals which are then injected into the class-D audio amplifier. The
3-level PWM scheme supports filterless speaker drive.
An adaptive DC-to-DC converter boosts the battery supply voltage in line with the output
of the SpeakerBoost protection algorithm. It switches to Follower mode (V
BST
=V
BAT
; no
boost) when the audio output voltage is lower than the battery voltage. Next to adaptive
DC to DC a PFM mode is selected when the requested output current is low. The adaptive
boost and PFM mode ensures a high efficiency ClassHD Amplifier.
It contains four TDM/I2S input/output (DIO) ports. These ports can be selected as an input
or an output on demand. i.e. DIO1 and DIO2, can be selected as the audio input stream.
DIO3 is provided to support stereo applications, while DIO4 can be used to provide stereo
AEC as well. DIO1, DIO3 and DIO4 are clocked by FS1 and BCK1, while DIO2 is clocked
by FS2 and BCK2; see Figure 1
).
DIO 3, 4 can be as well configured to transmit the DSP output signal, amplifier output
current and voltage information, or amplifier gain information. The gain information can be
used to facilitate communication between two devices in stereo applications.
