OP290_15 Datasheet, PDF (9/12 Pages) Analog Devices – Precision, Low Power, Micropower Dual Operational Amplifier

OP290
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
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.
80
60
40
20
0
0
500 1000 1500 2000 2500 3000 3500
HOURS
Figure 18. Lithium Sulphur Dioxide Cell Discharge Characteristic with OP290
and 100 kΩ Load
1kΩ
V_IN
+15V
+15V
1/2
OP290
A
OP37
V2
9kΩ
–15V
100Ω
10kΩ
1/2
OP290
B
–15V
V1 20V p-p @ 10Hz
CHANNEL
SEPARATION
=
20
log
V1
V2/1000
Figure 19. Channel Separation Test Circuit
Rev. C | Page 9 of 12