Texas Instruments DRV602 Evaluation Module DRV602EVM2 DRV602EVM2 Hoja De Datos
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DRV602EVM2
4.4
Using the DRV602 as a Differential Input, Second-Order Low-Pass Filter
R
2
R
2
R
1
R
3
C
1
C
1
C
3
R
1
R
3
C
3
-
In
+In
C
2
DRV602
Component Selection
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The resistor values should be low value to achieve low noise, but should be of high enough value to
obtain a small size ac-coupling capacitor. With the proposed values of 33 k
obtain a small size ac-coupling capacitor. With the proposed values of 33 k
Ω
, 68 k
Ω
, and 100 k
Ω
, a
dynamic range (DYR) of 102 dB can be achieved with a small 1-
µ
F input ac-coupling capacitor.
The MFB filter structure demands an op amp that is unity-gain stable at high frequencies; this requirement
can be relaxed by adding the C
can be relaxed by adding the C
X
capacitor value to be equal to C1. The DRV602 is unity-gain stable, but
stray capacitance and inductance from the PCB layout can affect the phase margin. Therefore, we
recommend adding C
recommend adding C
X
.
The single-ended input, second-order filter described in
can easily be extended to have a
differential input, as shown in
.
Figure 4. Differential Input, Second-Order Active Low-Pass Filter
C
2
can be split into separate capacitors to ground with the double value; this technique increases the
common-mode filtering. Another capacitor, C
X
, set equal to C
1
can continue to be used from the negative
input to ground to limit the high-frequency gain to 2.
As with the single-ended input, the differential input filter component values can be calculated with the
help of the TI
help of the TI
active filter design program available on the TI web site.
DRV602EVM2
6
SLOU248A – December 2008 – Revised January 2009