Datasheet

MAX9613 Evaluation Kit
Evaluates: MAX9613
_______________________________________________________________________________________ 3
ratio (CMRR) of the differential amplifier is determined
by the matching of the resistor ratios R5/R1 and R
C3
/R2
(Figure 2).
( )
OUT INP INM
V GAIN V V= −
where:
C3
R
R5
GAIN
R1 R2
= =
Sallen-Key Configuration
The Sallen-Key active filter topology is ideal for sensor
signal conditioning with a 2nd-order filter. These filters
benefit from a rail-to-rail input structure with no crossover
distortion, such as that available on the device.
Lowpass Sallen-Key Filter
To configure the Sallen-Key as a lowpass filter, populate
the R2 and R8 pads with resistors, and populate the C3
and C4 pads with capacitors. The corner frequency and
Q are then given by (Figure 3):
( )
C
1
ƒ
2 R2 C3 R8 C4
R2 C3 R8 C4
Q
C3 R2 R8
=
π × × ×
× × ×
=
+
Highpass Sallen-Key Filter
To configure the Sallen-Key as a highpass filter, populate
the C3 and C4 pads with resistors, and populate the R2
and R8 pads with capacitors. The corner frequency and
Q are then given by (Figure 4):
( )
C
R8 C4 R2 C3
R8 C4 R2 C3
C4 R2 R8
1
ƒ
2 C R C R
C R C R
Q
R C C
=
π × × ×
× × ×
=
+
Capacitive Loads
Some applications require driving large capacitive loads.
To improve the stability of the amplifier in such cases,
either replace R6 with a suitable resistor value to improve
amplifier phase margin in the presence of capacitive
load C9, or apply a resistive load in parallel with C9.
Figure 3. Lowpass 2nd-Order Filter Sallen-Key Configuration
for 10kHz
Figure 2. Differential Configuration with Gain +10
Figure 4. Generic 2nd-Order Highpass Sallen-Key Filter
INP
OUTA
INM
R8
0I
R6
0I
1
3
4
R2
1kI
1%
R5
10kI
1%
R
C3
10kI
1%
R1
1kI
1%
INP
OUTA
R8
2.74kI
C3
1nF
C4
4.7nF
R6
0I
1
3
4
R2
19.6kI
R5
0I
INP
OUTA
R
C3
C
R2
C
R8
R
C4
R6
0I
1
3
4
R5
0I