Datasheet

G
r
=
R
r
+ 100 k:
50 R
r
R
r
+IN
-IN
+
-
Preamplifier
Gain = 10
Output Buffer
Gain = K2
A1
A2
OFFSET
Internal
Resistor
100 k:
OUT
Level
shift
1
5
3 4
7
8
C
2
=
9
C
1
2
C
=
4
1
C
C
2
=
C
1
K
2

1
LMP8602, LMP8602Q, LMP8603, LMP8603Q
www.ti.com SNOSB36D –JULY 2009–REVISED MARCH 2013
For C
2
the value is calculated with:
(14)
Or for a gain = 5:
(15)
and for a gain = 10:
(16)
Note that the frequency response achieved using this procedure will only be accurate if the cut-off frequency of
the second order filter is much smaller than the intrinsic 60 kHz low-pass filter. In other words, to have the
frequency response of the LMP8602/LMP8602Q/LMP8603/LMP8603Q circuit chosen such that the internal poles
do not affect the external second order filter.
For a desired Q = 0.707 and a cut off frequency = 3 kHz, this will result for the LMP8602 in rounded values for
R2 = 51 kΩ, C1 = 1.5 nF and C2 = 3.9 nF
And for the LMP8603 this will result in rounded values for R2 = 22 kΩ, C1 = 3.3 nF and C2 = 0.39 nF
GAIN ADJUSTMENT
The gain of the LMP8602 is 50 and the gain of the LMP8603 is 100, however, this gain can be adjusted as the
signal path in between the two internal amplifiers is available on the external pins.
Reduce Gain
Figure 44 shows the configuration that can be used to reduce the gain of the LMP8602 and the LMP8603 in
unidirectional sensing applications.
Figure 44. Reduce Gain for Unidirectional Application
R
r
creates a resistive divider together with the internal 100 kΩ resistor such that, for the LMP8602, the reduced
gain G
r
becomes:
(17)
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Product Folder Links: LMP8602 LMP8602Q LMP8603 LMP8603Q