DRV604 Datasheet, PDF (12/21 Pages) Texas Instruments – DirectPath™ 2Vrms Line Driver and HP Amp With Adjustable Gain

DRV604
SLOS659 – JANUARY 2010
www.ti.com
Using the DRV604 as a 2nd order filter
Several audio DACs used today require an external low-pass filter to remove out of band noise. This is possible
with the DRV604 as it can be used like a standard OPAMP. Several filter topologies can be implemented both
single ended and differential. In the figure below a Multi Feed Back (MFB), with differential input and single
ended input is shown.
An AC-coupling capacitor to remove dc-content from the source is shown, it serves to block any dc content from
the source and lowers the dc-gain to 1 helping reducing the output dc-offset to minimum.
The component values can be calculated with the help of the TI FilterPro™ program available on the TI website
at:
http://focus.ti.com/docs/toolsw/folders/print/filterpro.html
Differential Input
R2
Inverting Input
R2
C3 _R1
R3
- In
C2
+ In
C3 ^R1
R3
C1
-
DRV604
+
C1
C3 _R1
R3
- In
C2
C1
-
DRV604
+
R2
Figure 15. 2^nd Order Active Low Pass Filter
The resistor values should have a low value for obtaining low noise, but should also have a high enough value to
get a small size ac-coupling cap. C2 can be split in two with the midpoint connected to GND, this can increase
the common-mode attenuation.
Pop-Free Power Up
Pop-free power up is ensured by keeping the EN_LD and EN_HP and/or Ex_UVP 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 EN_xx pins high, this way proper pre-charge of the ac-coupling is performed and pop-less
power-up is achieved. Figure 16 illustrates the preferred sequence.
Supply
Supply Ramp
EN_xx
Time for ac-coupling
capacitors to charge
Figure 16. Power-Up/Down Sequence
12
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