–

+

VO

CL

VI

2.5 V

TA = 25°C

f = 1 kHz

VI(PP) = 1 V

– 2.5 V

–

+

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

Figure 36. Test Circuit for Output Characteristics

TLC2810Z, TLC2810Y

LinCMOS

™ PRECISION

DUAL OPERATIONAL AMPLIFIERS

SLOS120A – AUGUST 1993 – REVISED AUGUST 1994

22

POST OFFICE BOX 655303

APPLICATION INFORMATION

output characteristics

The output stage of the TLC2810Z 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 TLC2810Z 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 35). 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

voltage offset from 0 V at the output occurs.

to N4, and the gain of the operational amplifier is

reduced at output voltage levels where N5 is not

supplying the output current.

All operating characteristics of the TLC2810Z are measured using a 20-pF load. The devices can drive 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 37). In many cases, adding some

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

(a) CL = 20 pF, RL = NO LOAD

(b) CL = 130 pF, RL = NO LOAD

(c) CL = 150 pF, RL = NO LOAD

Figure 37. Effect of Capacitive Loads