Datasheet OP290 (Analog Devices) - 9

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OP290 THEORY OF OPERATION BATTERY-POWERED APPLICATIONS INPUT VOLTAGE PROTECTION
The OP290 can be operated on a minimum supply voltage of The OP290 uses a PNP input stage with protection resistors in 1.6 V, or with dual supplies of ±0.8 V, and draws only 19 µA of series with the inverting and noninverting inputs. The high supply current. In many battery-powered circuits, the OP290 breakdown of the PNP transistors coupled with the protection can be continuously operated for thousands of hours before resistors provide a large amount of input protection, allowing requiring battery replacement, reducing equipment downtime the inputs to be taken 20 V beyond either supply without and operating cost. damaging the amplifier. High performance portable equipment and instruments
SINGLE-SUPPLY OUTPUT VOLTAGE RANGE
frequently use lithium cells because of their long shelf-life, light In single-supply operation, the OP290 input and output ranges weight, and high energy density relative to older primary cells. include ground. This allows true zero-in, zero-out operation. Most lithium cells have a nominal output voltage of 3 V and are The output stage provides an active pul -down to around 0.8 V noted for a flat discharge characteristic. The low supply voltage above ground. Below this level, a load resistance of up to 1 MΩ requirement of the OP290, combined with the flat discharge to ground is required to pul the output down to zero. characteristic of the lithium cel , indicates that the OP290 can be operated over the entire useful life of the cell. Figure 18 In the region from ground to 0.8 V, the OP290 has voltage gain shows the typical discharge characteristic of a 1 Ah lithium cel equal to the specification in Table 1. Output current source powering an OP290, with each amplifier, in turn, driving ful capability is maintained over the entire voltage range including output swing into a 100 kΩ load. ground.
100 ) V ( GE 80 OLTA LL V E C 60 E ID IOX D 40 R U H LP U S 20 M IU LITH 0 0 500 1000 1500 2000 2500 3000 3500
020
HOURS
00327- Figure 18. Lithium Sulphur Dioxide Cell Discharge Characteristic with OP290 and 100 kΩ Load
+15V +15V 1/2 OP290 1kΩ A OP37 V2 9kΩ 100Ω 10kΩ –15V –15V VIN 1/2 OP290 V1 20V p-p @ 10Hz B
019
V1 CHANNEL SEPARATION = 20 log V2/1000
00327- Figure 19. Channel Separation Test Circuit Rev. C | Page 9 of 12 Document Outline Features Pin Connections General Description Revision History Specifications Electrical Characteristics Absolute Maximum Ratings ESD Caution Typical Performance Characteristics Theory of Operation Battery-Powered Applications Input Voltage Protection Single-Supply Output Voltage Range Applications Information Temperature to 4 mA to 20 mA Transmitter Variable Slew Rate Filter Low Overhead Voltage Reference Outline Dimensions Ordering Guide