CLASS AB

CONTROL

GND

VCC

INN

INP

OUTPUT

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14

LPV511

SNOSAG7D – AUGUST 2005 – REVISED AUGUST 2016

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Copyright © 2005–2016, Texas Instruments Incorporated

7 Detailed Description

7.1 Overview

The LPV511 is a micropower operational amplifier that operates from a voltage supply range as wide as 2.7 V to

12 V with ensured specifications at 3 V, 5 V, and 12 V. The LPV511 exhibits an excellent speed-to-power ratio,

drawing only 880 nA of supply current with a bandwidth of 27 kHz.

7.2 Functional Block Diagram

7.3 Feature Description

The LPV511 has a rail-to-rail input which provides more flexibility for the system designer. As can be seen from

Functional Block Diagram, rail-to-rail input is achieved by using in parallel, one PNP differential pair and one

NPN differential pair. When the common mode input voltage (VCM) is near V

+, the NPN pair is on and the PNP

pair is off. When VCM is near V

−, the NPN pair is off and the PNP pair is on. When V

CM is between V

+ and V−,

internal logic decides how much current each differential pair will get. This special logic ensures stable and low

distortion amplifier operation within the entire common mode voltage range.

7.4 Device Functional Modes

7.4.1 Input Stage

Because both input stages have their own offset voltage (VOS) characteristic, the offset voltage of the LPV511

becomes a function of VCM. VOS has a crossover point at 1 V below V

+. See the V

OS vs VCM curve in Typical

Characteristics. Caution must be taken in situations where the input signal amplitude is comparable to the VOS

value and/or the design requires high accuracy. In these situations, it is necessary for the input signal to avoid

the crossover point.

The input bias current, IB will change in value and polarity as the input crosses the transition region. In addition,

parameters such as PSRR and CMRR which involve the input offset voltage will also be affected by changes in

VCM across the differential pair transition region.

Differential input voltage is the difference in voltage between the noninverting (+) input and the inverting input (

−)

of the op amp. Due to the three series diodes across the two inputs, the absolute maximum differential input

voltage is ±2.1 V. This may not be a problem to most conventional op amp designs; however, designers must

avoid using the LPV511 as a comparator.