–

+

R

P +

V

DD *

V

O

I

F )

I

L )

I

P

IP = Pullup Current

Required by the

Operational Amplifier

(typically 500

µA)

VO

VDD

RP

IP

IF

IL

RL

VI

R1

R2

–

+

VO

CL

Vi

2.5 V

TA = 25°C

f = 1 kHz

VI(PP) = 1 V

– 2.5 V

Figure 45. Test Circuit for Output Characteristics

TLV2342, TLV2342Y, TLV2344, TLV2344Y

LinCMOS

™ LOW-VOLTAGE HIGH-SPEED

OPERATIONAL AMPLIFIERS

SLOS194 – FEBRUARY 1997

28

POST OFFICE BOX 655303

APPLICATION INFORMATION

latch-up

Because CMOS devices are susceptible to latch-up due to their inherent parasitic thyristors, the TLV234x inputs

and outputs are 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.

output characteristics

The output stage of the TLV234x is designed to

sink and source relatively high amounts of current

(see Typical Characteristics). If the output is

subjected

to

a

short-circuit

condition,

this

high-current capability can cause device damage

under certain conditions. Output current capability

increases with supply voltage.

Although the TLV234x possesses excellent

high-level output voltage and current capability,

methods are available for boosting this capability

if needed. The simplest method involves the use

to the positive supply rail (see Figure 44). 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.

0 V at the output occurs. Secondly, pullup resistor

operational amplifier is reduced at output voltage

levels where N5 is not supplying the output

current.

All operating characteristics of the TLV234x are measured using a 20-pF load. The device drives higher

capacitive loads; however, as output load capacitance increases, the resulting response pole occurs at lower

frequencies thereby causing ringing, peaking, or even oscillation (see Figure 45 and Figure 46). In many cases,

adding some compensation in the form of a series resistor in the feedback loop alleviates the problem.