TFA9879 Datasheet, PDF (21/60 Pages) NXP Semiconductors – Mono BTL class-D audio amplifier for portable applications with digital input

NXP Semiconductors
TFA9879
Mono BTL class-D audio amplifier with digital input
Table 12. DRC attack and release rates
Control value:
attack rate^[1]
Attack rate (dB/ms)
0000
3
0001
2.7
0010^[3]
2.25
0011
1.8
0100
1.35
0101
0.9
0110
0.45
0111
0.225
1000
0.15
1001
0.11
1010
0.09
1011
0.075
1100
0.065
1101
0.06
1110
0.055
1111
0.05
Control value:
release rate^[2]
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010^[3]
1011
1100
1101
1110
1111
Release rate (dB/ms)
0.5
0.137
0.075
0.05
0.036
0.03
0.026
0.021
0.020
0.017
0.015
0.014
0.013
0.012
0.011
0.01
[1] The control value is selected via bits AT_RATE in the DRC control register (see Table 28).
[2] The control value is selected via bits RL_RATE in the DRC control register (see Table 28).
[3] Default value.
9.2.11 Power limiter
The power limiter controls the maximum output voltage in Amplifier mode. This feature
makes it possible to limit the output voltage across a peripheral (speaker) when
necessary.
The TFA9879 output voltage is dependent on:
• The analog supply voltage on pin V_DDP
• The gain of the power limiter (G)
• The power limiter input signal (X_i)
The bass/treble output signal is connected to the power limiter input and is relative to the
Fraction of Full Scale (FFS), from −1 to +1.
Equation 10 shows the relationship between these settings and the output voltage
between pins OUTA and OUTB in the audio bandwidth:
V_o
=
⎛
⎜
X_i
×
G
×
5.91
⎝^V_DDP
X_i × G × 5.91 < V_{DDP (V)}
X_I × G × 5.91 ≥ V_DDP
(10)
TFA9879
Product data sheet
Equation 10 only applies with no load and with clip control off (see Section 9.3). Clip
control and the R_DSon of the power switches reduce the maximum clipped output signal.
The power limiter gain can be reduced in 249 steps of 0.5 dB in the range 0 dB to
−124 dB.
All information provided in this document is subject to legal disclaimers.
Rev. 02 — 15 October 2010
© NXP B.V. 2010. All rights reserved.
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