Datasheet

fc
IN
+
1
2p R
IN
C
IN
C
IN
+
1
2p fc
IN
R
IN
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.
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 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 kΩ –2 × 6 37 kΩ 2.2 µF
82k5 –1 × 0.0 55 kΩ 1.5 µF
51k1 –1.5× 3.5 44 kΩ 2.2 µF
34k8 –2.3× 7.2 33 kΩ 3.3 µF
27k4 –2.5× 8 31 kΩ 3.3 µF
20k5 –3× 9.5 28 kΩ 3.3 µF
15k4 –3.5× 10.9 24 kΩ 3.3 µF
11k5 –4× 12 22 kΩ 4.7 µF
9k09 –5× 14 18 kΩ 4.7 µF
7k5 –5.6× 15 17 kΩ 4.7 µF
6k19 –6.4× 16.1 15 kΩ 6.8 µF
5k11 –8.3× 18.4 12 kΩ 6.8 µF
4k22 –10× 20 10 kΩ 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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