TLV521 datasheet(11/27 Pages) TI1

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TLV521

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SNOSD26 – MAY 2016

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7 Detailed Description

7.1 Overview

The TLV521 is fabricated with Texas Instruments' state-of-the-art VIP50 process. This proprietary process

dramatically improves the performance of Texas Instruments' low-power and low-voltage operational amplifiers.

The following sections showcase the advantages of the VIP50 process and highlight circuits which enable ultra-

low power consumption.

7.2 Functional Block Diagram

Figure 29. Block Diagram

7.3 Feature Description

The amplifier's differential inputs consist of a noninverting 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-)

(1)

where AOL is the open-loop gain of the amplifier, typically around 100 dB.

7.4 Device Functional Modes

7.4.1 Input Stage

The TLV521 has a rail-to-rail input which provides more flexibility for the system designer. Rail-to-rail input is

achieved by using in parallel, one PMOS differential pair and one NMOS differential pair. When the common

mode input voltage (VCM) is near V+, the NMOS pair is on and the PMOS pair is off. When VCM is near V−, the

NMOS pair is off and the PMOS pair is on. When VCM 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.

Because both input stages have their own offset voltage (VOS) characteristic, the offset voltage of the TLV521

becomes a function of VCM. VOS has a crossover point at 1.0 V below V+. Refer to the ’VOS vs. VCM’ curve in the

Typical Performance Characteristics section. Caution should 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. 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.

7.4.2 Output Stage

The TLV521 output voltage swings 3 mV from rails at 3.3-V supply, which provides the maximum possible

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

The TLV521 Maximum Output Voltage Swing defines the maximum swing possible under a particular output

load. The TLV521 output swings 50 mV from the rail at 5-V supply with an output load of 100 k

Ω.

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