TLC271 datasheet(62/84 Pages) TI

62 / 84 page

TLC271, TLC271A, TLC271B

LinCMOS

 PROGRAMMABLE LOW-POWER

OPERATIONAL AMPLIFIERS

SLOS090D – NOVEMBER 1987 – REVISED MARCH 2001

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

output characteristics (continued)

Although the TLC271 possesses excellent high-level output voltage and current capability, methods are

available for boosting this capability, if needed. The simplest method involves the use of a pullup resistor (RP)

connected from the output to the positive supply rail (see Figure 113). There are two disadvantages to the use

of this circuit. First, the NMOS pulldown transistor, N4 (see equivalent schematic) must sink a comparatively

large amount of current. In this circuit, N4 behaves like a linear resistor with an on-resistance between

approximately 60

Ω and 180 Ω, depending on how hard the operational amplifier input is driven. With very low

values of RP, a voltage offset from 0 V at the output occurs. Secondly, pullup resistor RP acts as a drain load

to N4 and the gain of the operational amplifier is reduced at output voltage levels where N5 is not supplying the

output current.

P +

–V

F )

L )

VDD

IP = Pullup current required

by the operational amplifier

(typically 500

µA)

–

Figure 113. Resistive Pullup to Increase VOH

5 V

BIAS SELECT

0.016

µF

Low Pass

High Pass

Band Pass

R = 5 k

Ω(3/d-1)

(see Note A)

0.016

µF

BIAS SELECT

5 V

10 k

Ω

10 k

Ω

10 k

Ω

5 V

BIAS SELECT

5 k

Ω

10 k

Ω

10 k

Ω

–

TLC271

–

TLC271

–

TLC271

NOTE B: d = damping factor, I/O

Figure 114. State-Variable Filter

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