OP290

Rev. C | Page 9 of 12

THEORY OF OPERATION

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 µA 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

frequently 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 18

shows the typical discharge characteristic of a 1 Ah lithium cell

powering an OP290, with each amplifier, in turn, driving full

output swing into a 100 kΩ load.

100

0

20

40

60

80

0

500

1000

1500

2000

2500

3000

3500

HOURS

Figure 18. Lithium Sulphur Dioxide Cell Discharge Characteristic with OP290

and 100 kΩ 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

damaging the amplifier.

SINGLE-SUPPLY OUTPUT VOLTAGE RANGE

In single-supply operation, the OP290 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 MΩ

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 specification in Table 1. Output current source

capability is maintained over the entire voltage range including

ground.

+15V

+15V

–15V

–15V

V2

VIN

1k

Ω

9k

Ω

100

Ω

10k

Ω

V1 20V p-p @ 10Hz

CHANNEL SEPARATION = 20 log

V1

V2/1000

1/2

OP290

A

1/2

OP290

B

OP37

Figure 19. Channel Separation Test Circuit