DRV602 Datasheet, PDF (8/12 Pages) Texas Instruments – DIRECTPATH™, 2Vrms Line Driver with Adjustable gain

DRV602
SLOS572 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
Input-Blocking Capacitors
DC input-blocking capacitors are required to be added in series with the audio signal into the input pins of the
DRV602. These capacitors block the DC portion of the audio source and allow the DRV602 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 1, then the frequency and/or capacitance can be determined when one of the
two values are given.
fc_IN
+
2p
1
R_IN
C_IN
or
C_IN
+
2p
1
fc_IN
R_IN
(1)
Using the DRV602 as 2^nd Order Filter
Several audio DACs used today require an external low-pass filter to remove out of band noise. This is possible
with the DRV602 as it can be used like a standard OPAMP.
Several filter topologies can be implemented both single ended and differential. In Figure 9, 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
Differential Input
R2
Inverting Input
R2
C3 _R1
R3
C1
- In
-
C2
DRV602
+
+ In
C3 ^R1
R3
C1
C3 _R1
R3
- In
C2
C1
-
DRV602
+
R2
Figure 9. 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. With the proposed values, 33k, 68k, 100k, a DNR of 102dB can be achieved
with a small 1µF input ac-coupling capacitor.
8
Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): DRV602