Datasheet

20
mV
/DIV
200 Ps/DIV
V
OUT
V
IN
V
S
= 5V
+
-
V
IN
R
ISO
V
OUT
C
L
LPV521
SNOSB14C –AUGUST 2009–REVISED FEBRUARY 2013 www.ti.com
Figure 66. Resistive Isolation of Capacitive Load
Recommended minimum values for R
ISO
are given in the following table, for 5V supply. Figure 67 shows the
typical response obtained with the C
L
= 50 pF and R
ISO
= 154 kΩ. The other values of R
ISO
in the table were
chosen to achieve similar dampening at their respective capacitive loads. Notice that for the LPV521 with larger
C
L
a smaller R
ISO
can be used for stability. However, for a given C
L
a larger R
ISO
will provide a more damped
response. For capacitive loads of 20 pF and below no isolation resistor is needed.
C
L
R
ISO
0 – 20 pF not needed
50 pF 154 kΩ
100 pF 118 kΩ
500 pF 52.3 kΩ
1 nF 33.2 kΩ
5 nF 17.4 kΩ
10 nF 13.3 kΩ
Figure 67. Step Response
EMI SUPPRESSION
The near-ubiquity of cellular, bluetooth, and Wi-Fi signals and the rapid rise of sensing systems incorporating
wireless radios make electromagnetic interference (EMI) an evermore important design consideration for
precision signal paths. Though RF signals lie outside the op amp band, RF carrier switching can modulate the
DC offset of the op amp. Also some common RF modulation schemes can induce down-converted components.
The added DC offset and the induced signals are amplified with the signal of interest and thus corrupt the
measurement. The LPV521 uses on chip filters to reject these unwanted RF signals at the inputs and power
supply pins; thereby preserving the integrity of the precision signal path.
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