16-Bit, 600 kSPS, Low Power Data Acquisition System for High Temperature Environments (CN0365)
A growing number of applications require data acquisition systems that must operate reliably at very high ambient temperature environments, such as downhole oil and gas drilling, avionics, and automotive. The circuit shown in Figure 1 is a 16-bit, 600 kSPS successive approximation analog-to-digital converter (ADC) system using devices rated, characterized, and guaranteed at 175°C. Because many of these harsh environment applications are battery-powered, the signal chain has been designed for low power consumption while still maintaining high performance.
Figure 1. High Temperature Data Acquisition System (Simplified Schematic: All Connections and Decoupling Not Shown)
This circuit uses the AD7981, a low power (4.65 mW at 600 kSPS), high temperature PulSAR® ADC, driven directly from the AD8634 high temperature, low power op amp. The AD7981 ADC requires an external voltage reference between 2.4 V and 5.1 V, and in this application, the voltage reference chosen is the micropower ADR225 precision 2.5 V reference, which is also qualified for high temperature operation and has a very low quiescent current of 60 μA maximum at 210°C.
All of the ICs in this design have packaging specially designed for high temperature environments, including monometallic wire bonds. In addition, this reference design describes the selection of the passive components, printed circuit board PCB) materials, and construction techniques to enable operation at these extreme temperatures. A complete design support package including bill of materials, schematic, assembly, and layout files is also available.
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