OPA743

9

SBOS201

APPLICATIONS INFORMATION

OPA743 series op amps can operate on 1.1mA quiescent

current from a single (or split) supply in the range of 3.5V

to 12V (

±1.75V to ±6V), making them highly versatile and

easy to use. The OPA743 is unity-gain stable and offers

7MHz bandwidth and 10V/

µs slew rate.

Rail-to-rail input and output swing helps maintain dynamic

range, especially in low supply applications. Figure 1 shows

the input and output waveforms for the OPA743 in unity-

gain configuration. On a

±6V supply with a 100kΩ load

100mV to the rail.

Power-supply pins should be bypassed with 1000pF ceramic

capacitors in parallel with 1

µF tantalum capacitors.

OPERATING VOLTAGE

OPA743 series op amps are fully specified and guaranteed

from 3.5V to 12V over a temperature range of –40ºC to

+85ºC. Parameters that vary significantly with operating

voltages or temperature are shown in the Typical Character-

istics.

RAIL-TO-RAIL INPUT

The input common-mode voltage range of the OPA743 series

extends 100mV beyond the supply rails at room temperature.

This is achieved with a complementary input stage—an N-

channel input differential pair in parallel with a P-channel

differential pair. The N-channel pair is active for input volt-

ages close to the positive rail, typically (V+) – 2.0V to 100mV

above the positive supply, while the P-channel pair is on for

inputs from 100mV below the negative supply to approxi-

mately (V+) – 1.5V. There is a small transition region,

typically (V+) – 2.0V to (V+) – 1.5V, in which both pairs are

on. This 500mV transition region can vary

±100mV with

process variation. Thus, the transition region (both stages on)

can range from (V+) – 2.1V to (V+) – 1.4V on the low end,

up to (V+) – 1.9V to (V+) – 1.6V on the high end. Most rail-

to-rail op amps on the market use this two input stage

approach, and exhibit a transition region where CMRR, offset

voltage, and THD may vary compared to operation outside

this region.

FIGURE 1. Rail-to-Rail Input and Output.

FIGURE 3. OPA743—No Phase Inversion with Inputs

Greater than the Power-Supply Voltage.

FIGURE 2. Input Current Protection for Voltages Exceeding

the Supply Voltage.

R

OPA743

10mA max

+V

V–

V

IN

V

OUT

I

OVERLOAD

INPUT VOLTAGE

Device inputs are protected by ESD diodes that will conduct if

the input voltages exceed the power supplies by more than

approximately 300mV. Momentary voltages greater than 300mV

beyond the power supply can be tolerated if the current is limited

to 10mA. This is easily accomplished with an input resistor, in

series with the op amp input as shown in Figure 2. Many input

signals are inherently current-limited to less than 10mA; there-

fore, a limiting resistor is not always required. The OPA743

features no phase inversion when the inputs extend beyond

supplies if the input current is limited, as seen in Figure 3.

Input

G = +1, V

Output (Inverted on osciloscope)

20

µs/div

8

6

4

2

0

–2

–4

–6

–8

V

20

µs/div

RAIL-TO-RAIL OUTPUT

A class AB output stage with common-source transistors is

used to achieve rail-to-rail output. This output stage is

capable of driving 1k

Ω loads connected to any point be-

tween V+ and V–. For light resistive loads (> 100k

Ω), the

output voltage can swing to 100mV from the supply rail.

With 1k

Ω resistive loads, the output can swing to within

325mV from the supply rails while maintaining high open-

loop gain (see the typical performance curve “Output Volt-

age Swing vs Output Current”).