TLC372, TLC372Q, TLC372Y

LinCMOS

™ DUAL DIFFERENTIAL COMPARATORS

SLCS114B – NOVEMBER 1983 – REVISED MARCH 1999

9

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

LinCMOS

The LinCMOS

™ process is a Linear polysilicon-gate complementary-MOS process. Primarily designed for

single-supply applications, LinCMOS

™ products facilitate the design of a wide range of high-performance

analog functions, from operational amplifiers to complex mixed-mode converters.

While digital designers are experienced with CMOS, MOS technologies are relatively new for analog designers.

This short guide is intended to answer the most frequently asked questions related to the quality and reliability

of LinCMOS

™ products. Further questions should be directed to the nearest TI field sales office.

electrostatic discharge

CMOS circuits are prone to gate oxide breakdown when exposed to high voltages even if the exposure is only

for very short periods of time. Electrostatic discharge (ESD) is one of the most common causes of damage to

CMOS devices. It can occur when a device is handled without proper consideration for environmental

electrostatic charges, e.g. during board assembly. If a circuit in which one amplifier from a dual operational

amplifier is being used and the unused pins are left open, high voltages tends to develop. If there is no provision

for ESD protection, these voltages may eventually punch through the gate oxide and cause the device to fail.

To prevent voltage buildup, each pin is protected by internal circuitry.

Standard ESD-protection circuits safely shunt the ESD current by providing a mechanism whereby one or more

transistors break down at voltages higher than the normal operating voltages but lower than the breakdown

voltage of the input gate. This type of protection scheme is limited by leakage currents which flow through the

shunting transistors during normal operation after an ESD voltage has occurred. Although these currents are

small, on the order of tens of nanoamps, CMOS amplifiers are often specified to draw input currents as low as

tens of picoamps.

To overcome this limitation, TI design engineers developed the patented ESD-protection circuit shown in

Figure 4. This circuit can withstand several successive 1-kV ESD pulses, while reducing or eliminating leakage

currents that may be drawn through the input pins. A more detailed discussion of the operation of TI’s ESD-

protection circuit is presented on the next page.

All input and output pins on LinCMOS and Advanced LinCMOS

™ products have associated ESD-protection

circuitry that undergoes qualification testing to withstand 1000 V discharged from a 100-pF capacitor through

a 1500-

Ω resistor (human body model) and 200 V from a 100-pF capacitor with no current-limiting resistor

(charged device model). These tests simulate both operator and machine handling of devices during normal

test and assembly operations.

D3

R2

Q2

To Protected Circuit

VDD

D2

D1

Q1

R1

Input

VSS

Figure 4. LinCMOS

™ ESD-Protection Schematic

Advanced LinCMOS is a trademark of Texas Instruments Incorporated.