Supply ramp

Supply

MUTE

Time for ac-coupling

capasitors to charge

fc

1

2p R

C

1

2p fc

or

TPA6139A2

www.ti.com

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.

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.

(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

Gain

INPUT

2 Hz

GAIN

RESISTOR

(dB)

RESISTANCE

Cutoff

249k

–2.0x

6.0

37k

2.2 µF

82k0

–1.0x

0.0

55k

1.5 µF

49k2

–1.5x

3.5

44k

2.2 µF

35k1

–2.3x

7.2

33k

3.3 µF

27k3

–2.5x

8.0

31k

3.3 µF

20k5

–3.0x

9.5

28k

3.3 µF

15k4

–3.5x

10.9

24k

3.3 µF

11k5

–4.0x

12.0

22k

4.7 µF

9k09

–5.0x

14.0

18k

4.7 µF

7k50

–5.6x

15.0

17k

4.7 µF

6k19

–6.4x

16.1

15k

6.8 µF

5k11

–8.3x

18.4

12k

6.8 µF

3k90

–10x

20.0

10k

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.

Figure 10. Power-Up Sequence

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