Datasheet

TFA9879 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2010. All rights reserved.
Product data sheet Rev. 02 — 15 October 2010 11 of 60
NXP Semiconductors
TFA9879
Mono BTL class-D audio amplifier with digital input
9.2 Digital Signal Processor (DSP) features
9.2.1 Serial interface selection
The TFA9879 contains two serial interfaces. The active interface is selected via bit
INPUT_SEL in the Device control register (see Table 21
). When this bit is toggled, the
following sequence is initiated:
• Soft mute is activated for 128/f
s
seconds
• The TFA9879 switches to Off mode and the serial interface input is toggled
• The TFA9879 switches back to Operating mode and soft mute is released
9.2.2 Mono selection
Mono selection is used to select the digital audio input channel to be amplified. The
options are:
• Left channel
• Right channel
• Left + right channels (sum divided by two)
Separate Mono selection is provided for the two serial interfaces via bits MONO_SEL in
the Serial interface control registers (addresses 01h and 03h; see Table 22
).
9.2.3 Programmable high-pass filter
The TFA9879 features a first-order high-pass filter on the digital audio input to block DC
and low frequency signals. DC values at the output can damage the speaker.
The high-pass filter cut-off frequency is determined by:
• The high-pass filter control setting (bits HP_CTRL, see Table 30)
• The sample frequency, f
s
The relationship between these parameters and the cut-off frequency is defined in
Equation 1
:
(1)
HP_CTRL can be programmed to any integer value between 0 and 511 (see Table 30
).
The high-pass filter is bypassed if HP_CTRL = 0 or bit HPF_BP in the Bypass control
register is set to 1 (see Table 27
).
9.2.4 De-emphasis
Digital de-emphasis is sometimes needed, especially with older recordings. Emphasis
and de-emphasis originate in the FM transmission, in which the Signal-to-Noise Ratio
(SNR) is not flat over the signal band (in fact the SNR gets worse as the signal frequency
increases). To achieve good SNR over the complete audio band, the high frequency
components of the audio signal were amplified prior to transmission (this is called
Emphasis).
f
high 3dB–()
f–
s
4096 HP_CTRL–
4096
---------------------------------------------
⎝⎠
⎛⎞
ln×
2π
----------------------------------------------------------------------
=