TLC274, TLC274A, TLC274B, TLC274Y, TLC279

LinCMOS

™ PRECISION QUAD OPERATIONAL AMPLIFIERS

SLOS092C – SEPTEMBER 1987 – REVISED MARCH 1998

33

POST OFFICE BOX 655303

APPLICATION INFORMATION

output characteristics (continued)

–

+

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 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 TLC274 and TLC279 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 TLC274 and

TLC279 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.

The current path established if latch-up occurs is usually between the positive supply rail and ground and can

be triggered by surges on the supply lines and/or voltages on either the output or inputs that exceed the supply

voltage. Once latch-up occurs, the current flow is limited only by the impedance of the power supply and the

forward resistance of the parasitic thyristor and usually results in the destruction of the device. The chance of

latch-up occurring increases with increasing temperature and supply voltages.