REV. A

OP290

–8–

1

7

4

5

6

3

2

8

+18V

–18V

100k

200

100k

1/2

OP290

1/2

OP290

Figure 2. Burn-In Circuit

APPLICATIONS INFORMATION

BATTERY-POWERED APPLICATIONS

The OP290 can be operated on a minimum supply voltage of

1.6 V, or with dual supplies of 0.8 V, and draws only 19 pA of

supply current. In many battery-powered circuits, the OP290

can be continuously operated for thousands of hours before

requiring battery replacement, reducing equipment downtime

and operating cost.

High-performance portable equipment and instruments fre-

quently use lithium cells because of their long shelf-life, light

weight, and high energy density relative to older primary cells.

Most lithium cells have a nominal output voltage of 3 V and are

noted for a flat discharge characteristic. The low supply voltage

requirement of the OP290, combined with the flat discharge

characteristic of the lithium cell, indicates that the OP290 can

be operated over the entire useful life of the cell. Figure 1 shows

the typical discharge characteristic of a 1 Ah lithium cell power-

ing an OP290 with each amplifier, in turn, driving full output

swing into a 100 k

Ω load.

INPUT VOLTAGE PROTECTION

The OP290 uses a PNP input stage with protection resistors in

series with the inverting and noninverting inputs. The high

breakdown of the PNP transistors coupled with the protection

resistors provide a large amount of input protection, allowing

the inputs to be taken 20 V beyond either supply without dam-

aging the amplifier.

SINGLE-SUPPLY OUTPUT VOLTAGE RANGE

In single-supply operation the OP290’s input and output ranges

include ground. This allows true “zero-in, zero-out” operation.

The output stage provides an active pull-down to around 0.8 V

above ground. Below this level, a load resistance of up to 1 MS2

to ground is required to pull the output down to zero.

In the region from ground to 0.8 V, the OP290 has voltage gain

equal to the data sheet specification. Output current source capa-

bility is maintained over the entire voltage range including ground.

+15V

+15V

–15V

–15V

V2

1k

9k

100

10k

V1 20Vp-p @ 10Hz

CHANNEL SEPARATION = 20 LOG

V1

V2/1000

1/2

OP290

A

1/2

OP290

B

OP37A

Figure 3. Channel Separation Test Circuit

APPLICATIONS

TEMPERATURE TO 4–20 mA TRANSMITTER

A simple temperature to 4–20 mA transmitter is shown in Figure 5.

After calibration, the transmitter is accurate to +0.5

°C over the

–50

°C to +150°C temperature range. The transmitter operates

from 8 V to 40 V with supply rejection better than 3 ppm/V.

the other half regulates the output current to satisfy the current

summation at its noninverting input.

I

VR

R

RR

V

RR R

RR

OUT

TEMP

SET

=

+

()









67

210

26

7

210

–

100

80

0

0

60

40

20

3500

3000

2500

500

1000

2000

1500

HOURS

Figure 4. Lithium Sulphur Dioxide Cell Discharge

Characteristic with OP290 and 100 k

Loads

The change in output current with temperature is the derivative

of the transfer function:

∆

∆

∆

∆

I

T

V

T

RR

RR

OUT

TEMP

=

+

()

67

210