TPA6139A2 Datasheet, PDF (11/22 Pages) Texas Instruments – DirectPath™ 25-mW Headphone Amplifier With Programmable-Fixed Gain

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TPA6139A2
SLOS700B – JANUARY 2011 – REVISED JUNE 2012
Input-Blocking Capacitors
DC input-blocking capacitors are required to be added in series with the audio signal into the input pins of the
TPA6139A2. These capacitors block the dc portion of the audio source and allow the TPA6139A2 inputs to be
properly biased to provide maximum performance. The input blocking capacitors also limit the DC gain to 1,
limiting the DC-offset voltage at the output.
These capacitors form a high-pass filter with the input resistor, R_IN. The cutoff frequency is calculated using
Equation 1. For this calculation, the capacitance used is the input-blocking capacitor and the resistance is the
input resistor chosen from Table 1. Then the frequency and/or capacitance can be determined when one of the
two values is given.
fc_IN
+
2p
1
R_IN
C_IN
or
C_IN
+
2p
1
fc_IN
R_IN
(1)
For a fixed cutoff frequency of 2Hz the size of the input capacitance is shown in the table below with the
capacitors rounded up to nearest E6 values. For 20Hz cutoff simply divide the capacitor values with 10; e.g., for
1x gain, 150nF is needed.
Table 2. Input Capacitor for Different Gain and Cutoff
Gain_set
RESISTOR
249k
82k0
49k2
35k1
27k3
20k5
15k4
11k5
9k09
7k50
6k19
5k11
3k90
GAIN
–2.0x
–1.0x
–1.5x
–2.3x
–2.5x
–3.0x
–3.5x
–4.0x
–5.0x
–5.6x
–6.4x
–8.3x
–10x
Gain
(dB)
6.0
0.0
3.5
7.2
8.0
9.5
10.9
12.0
14.0
15.0
16.1
18.4
20.0
INPUT
RESISTANCE
37k
55k
44k
33k
31k
28k
24k
22k
18k
17k
15k
12k
10k
2 Hz
Cutoff
2.2 µF
1.5 µF
2.2 µF
3.3 µF
3.3 µF
3.3 µF
3.3 µF
4.7 µF
4.7 µF
4.7 µF
6.8 µF
6.8 µF
10 µF
Pop-Free Power Up
Pop-free power up is ensured by keeping the MUTE low during power supply ramp up and down. The pin should
be kept low until the input AC-coupling capacitors are fully charged before asserting the MUTE pin high to pre-
charge the ac-coupling; and, pop-less power-up is achieved. Figure 10 illustrates the preferred sequence.
Supply
Supply ramp
MUTE
Time for ac-coupling
capasitors to charge
Figure 10. Power-Up Sequence
Copyright © 2011–2012, Texas Instruments Incorporated
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