V

+

VREF

VIN

VO

-

+

V

-

VOLTS

VREF

VO

TIME

VIN

LMV7271, LMV7272, LMV7275

SNOSA56I – FEBRUARY 2003 – REVISED SEPTEMBER 2015

www.ti.com

7 Detailed Description

7.1 Overview

A comparator is often used to convert an analog signal to a digital signal. As shown in Figure 24, the comparator

compares an input voltage (VIN) to a reference voltage (VREF). If VIN is less than VREF, the output (VO) is low.

However, if VIN is greater than VREF, the output voltage (VO) is high.

Figure 24. LMV7271 Basic Comparator

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Rail-to-Rail Input Stage

The LMV727X has an input common mode voltage range (VCM) of −0.1V below the V

− to 0.1 V above V+. This is

achieved by using paralleled PNP and NPN differential input pairs. When the VCM is near V

+, the NPN pair is on

and the PNP pair is off. When the VCM is near V

−, the NPN pair is off and the PNP pair is on. The crossover point

between the NPN and PNP input stages is around 950mV from V+. Because each input stage has its own offset

voltage (VOS), the VOS of the comparator becomes a function of the VCM. See curves for VOS vs. VCM in the

Typical Characteristics section. In application design, it is recommended to keep the VCM away from the

crossover point to avoid problems. The wide input voltage range makes LMV727X ideal in power supply

monitoring circuits, where the comparators are used to sense signals close to ground and power supplies.

12

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