fc

1

2p R

C

1

2p fc

or

Supply ramp

Supply

MUTE

_

Time for ac -coupling

capasitors to charge

DRV612

www.ti.com

SLOS690B

– DECEMBER 2010 – REVISED APRIL 2011

Input-Blocking Capacitors

DC input-blocking capacitors are required to be added in series with the audio signal into the input pins of the

DRV612. These capacitors block the dc portion of the audio source and allow the DRV612 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 2. Then the frequency and/or capacitance can be determined when one of the

two values is given.

(1)

For a fixed cutoff frequency of 2 Hz, the size of the input capacitance is shown in Table 2 with the capacitors

rounded up to nearest E6 values. For 20-Hz cutoff, simply divide the capacitor values with 10; e.g., for 1

× gain,

150 nF is needed.

Table 2. Input Capacitor for Different Gain and Cutoff

Gain_set

Gain

INPUT

2 Hz

GAIN

RESISTOR

(dB)

RESISTANCE

Cutoff

249 k

Ω

–2 ×

6

37 k

Ω

2.2

µF

82k5

–1 ×

0.0

55 k

Ω

1.5

µF

51k1

–1.5×

3.5

44 k

Ω

2.2

µF

34k8

–2.3×

7.2

33 k

Ω

3.3

µF

27k4

–2.5×

8

31 k

Ω

3.3

µF

20k5

–3×

9.5

28 k

Ω

3.3

µF

15k4

–3.5×

10.9

24 k

Ω

3.3

µF

11k5

–4×

12

22 k

Ω

4.7

µF

9k09

–5×

14

18 k

Ω

4.7

µF

7k5

–5.6×

15

17 k

Ω

4.7

µF

6k19

–6.4×

16.1

15 k

Ω

6.8

µF

5k11

–8.3×

18.4

12 k

Ω

6.8

µF

4k22

–10×

20

10 k

Ω

10

µF

Pop-Free Power Up

Pop-free power up is ensured by keeping the MUTE pin low during power-supply ramp-up and -down. The pins

should be kept low until the input ac-coupling capacitors are fully charged before asserting the MUTE pin high,

this way proper pre-charge of the ac-coupling is performed and pop-less power up is achieved. Figure 9

illustrates the preferred sequence.

Figure 9. Power-Up/Down Sequence

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© 2010–2011, Texas Instruments Incorporated

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