OUT

V

+

V

–

IN –

IN +

Copyright © 2016,

Texas Instruments Incorporated

13

LPV811, LPV812

www.ti.com

SNOSD33B – NOVEMBER 2016 – REVISED NOVEMBER 2016

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Copyright © 2016, Texas Instruments Incorporated

7 Detailed Description

7.1 Overview

The LPV811 (single) and LPV812 (dual) series of nanoPower CMOS operational amplifiers are designed for

long-life battery-powered and energy harvested applications. They operate on a single supply with operation as

low as 1.6V. The Input Offset is trimmed to less than 300uV and the output is rail-to-rail and swings to within

3.5mV of the supplies with a 100kΩ load. The common-mode range extends to the negative supply making it

ideal for single-supply applications. EMI protection has been employed internally to reduce the effects of EMI.

Parameters that vary significantly with operating voltages or temperature are shown in the Typical Characteristics

curves.

7.2 Functional Block Diagram

7.3 Feature Description

The amplifier's differential inputs consist of a non-inverting input (+IN) and an inverting input (–IN). The amplifier

amplifies only the difference in voltage between the two inputs, which is called the differential input voltage. The

output voltage of the op-amp VOUT is given by Equation 1:

VOUT = AOL (IN

+ – IN–)

where

•

AOL is the open-loop gain of the amplifier, typically around 120 dB (1,000,000x, or 1,000,000 Volts per

microvolt).

(1)

7.4 Device Functional Modes

7.4.1 Negative-Rail Sensing Input

The input common-mode voltage range of the LPV81x extends from (V-) to (V+) – 0.9 V. In this range, low offset

can be expected with a minimum of 77dB CMRR. The LPV81x is protected from output "inversions" or

"reversals".

7.4.2 Rail to Rail Output Stage

The LPV81x output voltage swings 3.5 mV from rails at 1.8 V supply, which provides the maximum possible

dynamic range at the output. This is particularly important when operating on low supply voltages.

The LPV81x Maximum Output Voltage Swing graph defines the maximum swing possible under a particular

output load.

7.4.3 Design Optimization for Nanopower Operation

When designing for ultra-low power, choose system feedback components carefully. To minimize quiescent

current consumption, select large-value feedback resistors. Any large resistors will react with stray capacitance in

the circuit and the input capacitance of the operational amplifier. These parasitic RC combinations can affect the

stability of the overall system. A feedback capacitor may be required to assure stability and limit overshoot or

gain peaking.

When possible, use AC coupling and AC feedback to reduce static current draw through the feedback elements.

Use film or ceramic capacitors since large electrolytics may have large static leakage currents in the nanoamps.