OP490
Figure 1. Lithium-Sulphur Dioxide Cell Discharge Charac-
teristic with OP490 and 100 k
Ω
Loads
requirement of the OP490, combined with the flat discharge
characteristic of the lithium cell, indicates that the OP490 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 OP490 with each amplifier, in turn, driving full output
swing into a 100 kΩ load.
SINGLE-SUPPLY OUTPUT VOLTAGE RANGE
Channel Separation Test Circuit
APPLICATIONS INFORMATION
BATTERY-POWERED APPLICATIONS
In single-supply operation the OP490’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 MΩ
to ground is required to pull the output down to zero.
In the region from ground to 0.8 V the OP490 has voltage gain
equal to the data sheet specification. Output current source ca-
pability is maintained over the entire voltage range including
ground.
INPUT VOLTAGE PROTECTION
The OP490 can be operated on a minimum supply voltage of
+1.6 V, or with dual supplies of
±
0.8 V, and draws only 60
µA
of supply current. In many battery-powered circuits, the OP490
can be continuously operated for hundreds of hours before re-
quiring battery replacement, reducing equipment downtime and
operating costs.
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 current
The OP490 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 provides a large amount of input protection, allowing
the inputs to be taken 20 V beyond either supply without dam-
aging the amplifier.
–8–
REV. B
AD [ ANALOG DEVICES ]
