10 M:

-

+

10 M:

10 M:

10 M:

10 M:

270 pF

270 pF

270 pF

CR2032 Coin Cell

225 mAh = 5 circuits @ 9.5 yrs.

60 Hz Twin T Notch Filter

10 M:

270 pF

Remote Sensor

Signal

+

60 Hz

To ADC

Signal × 2

(No 60 Hz)

LPV542

SNOSCX9 – MARCH 2015

www.ti.com

8 Application and Implementation

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

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

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:

(2)

To achieve a 60 Hz notch use R = 10 M

Ω and C = 270 pF. If eliminating 50 Hz noise, which is common in

European systems, use R = 11.8 M

Ω and C = 270 pF.

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.

16

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