POWER AND LINEAR IC SOLUTIONS

ADC Digitises Precision Barometric Pressure Measurement

The LTC2450 from Linear Technology Corporation is a 16-bit, single-ended input, delta sigma ADC (Analogue/Digital Converter) in a 2mm x 2mm DFN package. It can digitise even the most accurate sensor measurements, such as those obtained from the Setra Model 270, a highly sensitive barometric pressure sensor commonly used in weather stations and semiconductor manufacture.

The LTC2450 has impressive DC specifications, including 2LSB INL (Integral NonLinearity), 2LSB offset and 0.01% gain error. This makes it a good match for many high-end industrial sensors and a wide variety of data acquisition, measurement, control and general-purpose voltage monitoring applications.

The Setra Model 270 is an extremely accurate barometric-pressure sensor with an input range of 600millibar to 1100millibar, corresponding to a 0V to 5V output. However, an expensive ADC is not required to take full advantage of its performance; the LTC2450 is more than adequate for the sensor’s 0.05% accuracy.



The sensor produces a balanced output and is equivalent to a four terminal device when connected to the ADC (as illustrated in the diagram).

The Setra Model 270 is sufficiently accurate to monitor changes in pressure resulting from walking slowly up and down a flight of stairs (as in the graph). When at rest in this process, it responds to subtle changes in ambient pressure, such as those caused by the opening and closing of a door.

The LTC2450 is inherently very accurate; it can perform on-chip averaging, improving resolution without an increase in external processing and firmware requirements. The front-end sample rate of the device is 3.9MSPS, decimated to 30SPS by a digital filter with a bandwidth of approximately 30Hz. This greatly attenuates noise between 30Hz and 3.9MHz; a simple one-pole filter is sufficient to eliminate wideband noise.

A further feature of the LTC2450 is a proprietary modulator-switching scheme that reduces the average input current. The very low 50nA-average sampling current of the LTC2450 produces less than 1LSB error with a 1kΩ, 0.1μF filter. This filter is more than adequate for limiting the wideband noise of most active devices driving the ADC and reduces the effects of sampling current spikes from the modulator on the source.



Features

• Ultra tiny 16-bit delta sigma ADC
• 3.9MSPS front-end sampling rate: 30 conversions per second
• 0.02LSB RMS noise
• 2LSB INL, no missing codes
• 2LSB offset error
• 4LSB full-scale error
• SPI interface
• Integrated oscillator
• Single conversion settling time
• Single cycle operation
• 350µA supply current
• 50nA sleep current
• Single 2.7V to 5.5V supply
• Six pin, 2mm x 2mm DFN package

Applications

• Instrumentation and sensor interfacing

For further information, to register your interest in a Free Demo Board*, or to obtain a copy of the latest Altera/LTC Development Tools Brochure, please click here

* Free demo boards are limited to current or potential Arrow customers with valid opportunities and are at the discretion of local Arrow representatives.