- In

DifferentialInput

InvertingInput

DRV604

R1

R1

R2

R2

+

-

C3

C3

R3

R3

C1

C1

C2

+ In

- In

DRV604

R1

R2

+

-

C3

R3

C1

C2

SupplyRamp

Supply

EN_xx

Timeforac-coupling

capacitorstocharge

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

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.

Figure 16. Power-Up/Down Sequence

12

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