LPV542 Datasheet, PDF (16/29 Pages) Texas Instruments – LPV542 Dual Nanopower 1.8 V, 490nA, RRIO CMOS Operational Amplifier

LPV542
SNOSCX9 – MARCH 2015
8 Application and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LPV542 is a ultra-low power operational amplifier that provides 8 kHz bandwidth with only 490nA quiescent
current, and near precision offset and drift specifications at a low cost. These rail-to-rail input and output
amplifiers are specifically designed for battery-powered applications. The input common-mode voltage range
extends to the power-supply rails and the output swings to within millivolts of the rails, maintaining a wide
dynamic range.
8.2 Typical Application: 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 39. 60 Hz Notch Filter
8.2.1 Design Requirements
Small signals from transducers in remote and distributed sensing applications commonly suffer strong 60 Hz
interference from AC power lines. The circuit of Figure 39 notches out the 60 Hz and provides a gain A_V = 2 for
the sensor signal represented by a 1 kHz sine wave. Similar stages may be cascaded to remove 2^nd and 3^rd
harmonics of 60 Hz. Thanks to the nA power consumption of the LPV542, even 5 such circuits can run for 9.5
years from a small CR2032 lithium cell. These batteries have a nominal voltage of 3 V and an end of life voltage
of 2 V. With an operating voltage from 1.6 V to 5.5 V the LPV542 can function over this voltage range.
8.2.2 Detailed Design Procedure
The notch frequency is set by:
F₀ = 1 / 2πRC.
(2)
To achieve a 60 Hz notch use R = 10 MΩ and C = 270 pF. If eliminating 50 Hz noise, which is common in
European systems, use R = 11.8 MΩ and C = 270 pF.
The Twin T Notch Filter works by having two separate paths from V_IN to the amplifier’s input. A low frequency
path through the series input resistors and another separate high frequency path through the series input
capacitors. However, at frequencies around the notch frequency, the two paths have opposing phase angles and
the two signals will tend to cancel at the amplifier’s input.
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