Datasheet
fc
IN
+
1
2p R
IN
C
IN
C
IN
+
1
2p fc
IN
R
IN
or
--IN
DifferentialInput
InvertingInput
DRV603
R1
R1
R2
R2
+
-
C3
C3
R3
R3
C1
C1
C2
R1
R2
+
-
C3
R3
C1
C2
+IN
-IN
DRV603
DRV603
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SLOS617C –JANUARY 2009–REVISED NOVEMBER 2009
INPUT-BLOCKING CAPACITORS
DC input-blocking capacitors are required to be added in series with the audio signal into the input pins of the
DRV603. These capacitors block the dc portion of the audio source and allow the DRV603 inputs to be properly
biased to provide maximum performance.
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 1. Then the frequency and/or capacitance can be determined when one of the
two values is given.
(1)
USING THE DRV603 AS A SECOND-ORDER FILTER
Several audio DACs used today require an external low-pass filter to remove out-of-band noise. This is possible
with the DRV603, as it can be used like a standard OPAMP. Several filter topologies can be implemented, both
single-ended and differential. In Figure 13 , a multi-feedback (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
Figure 13. Second-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 capacitor. Using 5.6 kΩ for the resistors, C1 = 220 pF, and C2 = 470 pF, a DNR of
112 dB can be achieved with a 10-μF input ac-coupling capacitor.
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Product Folder Link(s): DRV603