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AD590JR Datasheet(PDF) 6 Page - Analog Devices |
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AD590JR Datasheet(HTML) 6 Page - Analog Devices |
6 / 16 page AD590 Data Sheet Rev. G | Page 6 of 16 PRODUCT DESCRIPTION The AD590 is a 2-terminal temperature-to-voltage transducer. It is available in a variety of accuracy grades and packages. When using the AD590 in die form, the chip substrate must be kept electrically isolated (floating) for correct circuit operation. Figure 6. Metallization Diagram The AD590 uses a fundamental property of the silicon transistors from which it is made to realize its temperature proportional characteristic: if two identical transistors are operated at a constant ratio of collector current densities, r, then the difference in their base-emitter voltage is (kT/q)(In r). Because both k (Boltzman’s constant) and q (the charge of an electron) are constant, the resulting voltage is directly pro- portional to absolute temperature (PTAT). (For a more detailed description, see M.P. Timko, “A Two-Terminal IC Temperature Transducer,” IEEE J. Solid State Circuits, Vol. SC-11, p. 784-788, Dec. 1976. Understanding the Specifications–AD590.) In the AD590, this PTAT voltage is converted to a PTAT current by low temperature coefficient thin-film resistors. The total current of the device is then forced to be a multiple of this PTAT current. Figure 7 is the schematic diagram of the AD590. In this figure, Q8 and Q11 are the transistors that produce the PTAT voltage. R5 and R6 convert the voltage to current. Q10, whose collector current tracks the collector currents in Q9 and Q11, supplies all the bias and substrate leakage current for the rest of the circuit, forcing the total current to be PTAT. R5 and R6 are laser-trimmed on the wafer to calibrate the device at 25°C. Figure 8 shows the typical V–I characteristic of the circuit at 25°C and the temperature extremes. Figure 7. Schematic Diagram Figure 8. V–I Plot 1725µM 1090µM V– V+ Q1 Q2 R2 1040Ω Q5 Q3 Q4 C1 26pF Q6 Q7 Q12 R4 11kΩ Q8 Q10 Q9 CHIP SUBSTRATE Q11 1 1 8 R5 146Ω R6 820Ω R1 260Ω + – R3 5kΩ 01 2 +150°C 423 298 218 +25°C –55°C 34 SUPPLY VOLTAGE (V) 56 30 |
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