TLC27M4, TLC27M4A, TLC27M4B, TLC27M4Y, TLC27M9

LinCMOS

™ PRECISION QUAD OPERATIONAL AMPLIFIERS

SLOS093C – OCTOBER 1987 – REVISED MAY 1999

33

POST OFFICE BOX 655303

APPLICATION INFORMATION

output characteristics (continued)

Although the TLC27M4 and TLC27M9 possess excellent high-level output voltage and current capability,

methods for boosting this capability are available, if needed. The simplest method involves the use of a pullup

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

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

the output current.

–

+

VI

VDD

RP

VO

R2

R1

RL

IP

IF

IL

C

IP = Pullup current required

by the operational amplifier

(typically 500

µA)

VO

Rp =

VDD – VO

IF + IL + IP

Figure 42. Resistive Pullup

Figure 43. Compensation for

Input Capacitance

feedback

Operational amplifier circuits nearly always employ feedback, and since feedback is the first prerequisite for

oscillation, some caution is appropriate. Most oscillation problems result from driving capacitive loads

(discussed previously) and ignoring stray input capacitance. A small-value capacitor connected in parallel with

the feedback resistor is an effective remedy (see Figure 43). The value of this capacitor is optimized empirically.

electrostatic discharge protection

The TLC27M4 and TLC27M9 incorporate an internal electrostatic discharge (ESD) protection circuit that

prevents functional failures at voltages up to 2000 V as tested under MIL-STD-883C, Method 3015.2. Care

should be exercised, however, when handling these devices, as exposure to ESD may result in the degradation

of the device parametric performance. The protection circuit also causes the input bias currents to be

temperature-dependent and have the characteristics of a reverse-biased diode.

latch-up

Because CMOS devices are susceptible to latch-up due to their inherent parasitic thyristors, the TLC27M4 and

TLC27M9 inputs and outputs were designed to withstand – 100-mA surge currents without sustaining latch-up;

however, techniques should be used to reduce the chance of latch-up whenever possible. Internal protection

diodes should not, by design, be forward biased. Applied input and output voltage should not exceed the supply

voltage by more than 300 mV. Care should be exercised when using capacitive coupling on pulse generators.

Supply transients should be shunted by the use of decoupling capacitors (0.1

µF typical) located across the

supply rails as close to the device as possible.