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OP90GPZ Datasheet(PDF) 8 Page - Analog Devices |
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OP90GPZ Datasheet(HTML) 8 Page - Analog Devices |
8 / 13 page OP90 –8– Single-Supply Output Voltage Range In single-supply operation, the OP90’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 M Ω to ground is required to pull the output down to zero. In the region from ground to 0.8 V, the OP90 has voltage gain equal to the data sheet specification. Output current source capatibility is maintained over the entire voltage range includ- ing ground. APPLICATIONS Battery-Powered Voltage Reference The circuit of Figure 6 is a battery-powered voltage reference that draws only 17 µA of supply current. At this level, two AA cells can power this reference over 18 months. At an output voltage of 1.23 V @ 25 °C, drift of the reference is only at 5.5 µV/°C over the industrial temperature range. Load regulation is 85 µV/mA with line regulation at 120 µV/V. Design of the reference is based on the bandgap technique. Scaling of resistors R1 and R2 produces unequal currents in Q1 and Q2. The resulting VBE mismatch creates a temperature proportional voltage across R3 which, in turn, produces a larger temperature-proportional voltage across R4 and R5. This volt- age appears at the output added to the VBE of Q1, which has an opposite temperature coefficient. Adjusting the output to l.23 V at 25 °C produces minimum drift over temperature. Bandgap references can have start-up problems. With no current in R1 and R2, the OP90 is beyond its positive input range limit and has an undefined output state. Shorting Pin 5 (an offset adjust pin) to ground, forces the output high under these conditions and ensures reliable start-up without significantly degrading the OP90’s offset drift. 4 2 3 5 6 7 OP90 R1 240k R2 1.5M C1 1000pF V+ (2.5V TO 36V) VOUT (1.23V @ 25 C) 6 5 7 3 2 1 R3 68k R4 130k R5 20k OUTPUT ADJUST MAT-01AH Figure 6. Battery-Powered Voltage Reference HOURS 4 3 0 0 2000 7000 4000 2 1 1000 3000 6000 5000 Figure 3. Lithium Sulphur Dioxide Cell Discharge Characteristic with OP90 and 100 k Ω Load Input Voltage Protection The OP90 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. Offset Nulling The offset null circuit of Figure 4 provides 6 mV of offset adjust- ment range. A 100 k Ω resistor placed in a series with the wiper of the offset null potentiometer, as shown in Figure 5, reduces the offset adjustment range to 400 µV and is recommended for applications requiring high null resolution. Offset nulling does not affect TCVOS performance. TEST CIRCUITS V+ 1 2 3 5 6 7 OP90 4 100k V– Figure 4. Offset Nulling Circuit V+ 1 2 3 5 6 7 OP90 4 100k V– 100k Figure 5. High Resolution Offset Nulling Circuit REV. C |
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