1. General description
The TFA9891 is a high efficiency class-D audio amplifier with a sophisticated speaker
boost and protection algorithm. It can deliver 7.2 W peak output power to an 8 speaker,
at a supply voltage of 3.6 V. The internal boost converter raises the supply voltage to
9.5 V, providing ample headroom for major improvements in sound quality.
A safe working environment is provided for the speaker under all operating conditions.
The TFA9891 maximizes acoustic output while ensuring that the diaphragm displacement
and voice coil temperature do not exceed their rated limits. This function is based on a
speaker box model that operates in all loudspeaker environments (e.g. free air, closed box
or vented box). Furthermore, advanced signal processing ensures that the quality of the
audio signal is never degraded by unwanted clipping or distortion in the amplifier or
speaker. An integrated Dynamic Range Compressor (DRC) allows the speaker to operate
at the highest possible power rating without suffering physical damage.
Unlike competing solutions, the adaptive sound maximizer algorithm uses feedback to
calculate both the temperature and the excursion. It allows the TFA9891 to adapt to
changes in the acoustic environment.
Internal intelligent DC-to-DC conversion boosts the supply rail to provide additional
headroom and power output. The supply voltage is only raised when necessary. It
maximizes the output power of the class-D audio amplifier while limiting quiescent power
consumption.
The TFA9891 also incorporates advanced battery protection. By limiting the supply
current when the battery voltage is low, it prevents the audio system from drawing
excessive load currents from the battery. Drawing excessive load currents from the
battery could cause a system undervoltage. The advanced processor minimizes the
impact of a falling battery voltage on the audio quality, by preventing distortion as the
battery discharges.
The device features low RF susceptibility because it has a digital input interface that is
insensitive to clock jitter. The second order closed loop architecture used in a class-D
audio amplifier provides excellent audio performance and high supply voltage ripple
rejection. The audio input interface is I
2
S and the control settings are communicated via
an I
2
C-bus interface.
The device also provides the speaker with robust protection against ESD damage. In a
typical application, no additional components are required to withstand a 15 kV discharge
on the speaker.
The TFA9891 is available in a 49-bump WLCSP (Wafer Level Chip-Size Package) with a
400 m pitch.
TFA9891
9.5 V boosted audio system with adaptive sound maximizer
and speaker protection
Rev. 1 — 21 December 2016 Product short data sheet
