LPV521MGX Datasheet, PDF (22/29 Pages) Texas Instruments – LPV521 Nanopower, 1.8V, RRIO, CMOS Input, Operational Amplifier

LPV521
SNOSB14C – AUGUST 2009 – REVISED FEBRUARY 2013
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-
V_IN
+
R_ISO
C_L
V_OUT
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
0 – 20 pF
50 pF
100 pF
500 pF
1 nF
5 nF
10 nF
R_ISO
not needed
154 kΩ
118 kΩ
52.3 kΩ
33.2 kΩ
17.4 kΩ
13.3 kΩ
V_IN
V_OUT
V_S = 5V
200 Ps/DIV
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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