LPV521_15 Datasheet, PDF (21/33 Pages) Texas Instruments – LPV521 NanoPower, 1.8-V, RRIO, CMOS Input, Operational Amplifier

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V_IN
V_OUT
LPV521
SNOSB14D – AUGUST 2009 – REVISED DECEMBER 2014
V_S = 5V
200 2s/DIV
Figure 63. Step Response
8.1.2 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.
Twisted pair cabling and the active front-end’s common-mode rejection provide immunity against low-frequency
noise (i.e. 60-Hz or 50-Hz mains) but are ineffective against RF interference. Even a few centimeters of PCB
trace and wiring for sensors located close to the amplifier can pick up significant 1 GHz RF. The integrated EMI
filters of the LPV521 reduce or eliminate external shielding and filtering requirements, thereby increasing system
robustness. A larger EMIRR means more rejection of the RF interference. For more information on EMIRR,
please refer to AN-1698.
8.2 Typical Applications
8.2.1 60-Hz Twin T-Notch Filter
V_BATT = 3V o2V @ end of life
CR2032 Coin Cell
225 mAh = 5 circuits @ 9.5 yrs.
Remote Sensor
V_IN
Signal
+
60 Hz
10 M:
10 M:
10 M:
270 pF
10 M:
10 M:
270 pF
10 M:
V_BATT
-
+
V_OUT
60 Hz Twin T Notch Filter
A_V = 2 V/V
To ADC
Signal × 2
(No 60 Hz)
270 pF 270 pF
Figure 64. 60-Hz Notch Filter
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