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LTC2402 LTC2402

Application Notes

• Download
  Delta Sigma ADC Bridge Measurement Techniques &mdash AN96
  PDF, 232 Kb, File published: Jan 17, 2005
  AN96 features several applications that demonstrate how to take full advantage of Linear Technology's delta sigma ADCs when interfacing to sensors. In many cases, signal conditioning can be greatly simplified or eliminated completely. This note explains where it is appropriate to use amplifiers and how to optimize amplifier gain. Also included are discussions on measuring effective number of bits (ENOB) and the relationship to instrument performance, frequency response of delta sigma ADCs, and test techniques. C source code for all of the applications is included to aid firmware development.
  Extract from the document

  Application Note 96
  January 2005
  Delta Sigma ADC Bridge Measurement Techniques
  Mark Thoren
  Introduction In a typical 12-bit measurement system, the signal conditioning amplifier requires a very high gain in order to make
  use of the full ADC input range. A sensor with a 10mV fullscale output requires a gain of 500 to use the full input
  range of a typical 5V input ADC. A filter may be required to
  reduce noise at the expense of settling time. Additional
  difficulties arise when dealing with the large common
  mode voltage typical of a bridge sensor. Most instrumentation amplifiers have a large discrepancy between the
  typical CMRR and guaranteed minimum, which may require an additional trim. Sensors for pressure, load, temperature, acceleration and
  many other physical quantities often take the form of a
  Wheatstone bridge. These sensors can be extremely linear
  and stable over time and temperature. However, most
  things in nature are only linear if you don’t bend them too
  much. In the case of a load cell, Hooke’s law states that the
  strain in a material is proportional to the applied stress—
  as long as the stress is nowhere near the material’s yield
  point (the “point of no return” where the material is
  permanently deformed). The consequence is that a load
  cell based on a resistance strain gauge will have a very
  small electrical output—often only a few millivolts. In
  spite of this, instruments with 100,000 counts of resolution and more are possible. This Application Note presents …

Design Notes

• Download
  1- and 2-Channel No Latency О”ОЈв„ў 24-Bit ADCs Easily Digitize a Variety of Sensors, Part 1 &mdash DN236
  PDF, 96 Kb, File published: Jul 10, 2001
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  1-and 2-Channel No Latency ∆Σ™ 24-Bit ADCs Easily Digitize
  a Variety of Sensors, Part 1 – Design Note 236
  Michael K. Mayes 1. Ultralow offset (1ppm), offset drift (0.01ppm/В°C), fullscale error (4ppm) and full-scale drift (0.02ppm/В°C)
  without user calibration
  2. Absolute accuracy less than 10ppm total (linearity
  + offset + full scale + noise) over the full operating
  temperature range
  3. Ease-of-use (eight pins, no configuration registers,
  internal oscillator and latency-free conversion)
  4. Low noise and wide dynamic range (0.3ppm RMS
  with VREF = VCC = 5V)
  This two part Design Note introduces two new products
  leveraging the technology used in the LTC2400. Both
  parts are in tiny 10-pin MSOP packages. They include
  full-scale and zero-scale set inputs for removing systematic offset/full-scale errors. The п¬Ѓrst part (LTC2401) is
  a single-ended 1-channel device. The second part is a
  2-channel device with automatic ping-pong channel
  selection (LTC2402).
  The absolute accuracy and near zero drift of these devices enable several novel applications, of which two are
  presented in Part 1 and two in Part 2. The п¬Ѓrst application
  uses the full-scale set (FSSET) and zero-scale set (ZSSET)
  inputs of the 1-channel device (LTC2401) to digitize a
  half-bridge sensor. The second combines the LTC2402’s …

• Download
  1- and 2-Channel No Latency О”ОЈв„ў 24-Bit ADCs Easily Digitize a Variety of Sensors, Part 2 &mdash DN237
  PDF, 73 Kb, File published: Jul 20, 2001
  Extract from the document

  1-and 2-Channel No Latency ∆Σ™ 24-Bit ADCs Easily Digitize
  a Variety of Sensors, Part 2 – Design Note 237
  Michael K. Mayes
  Introduction
  This Design Note is a continuation of application
  ideas using the LTC В®2401/LTC2402 high accuracy,
  tiny (MSOP), 24-bit delta-sigma converters. Part 1
  introduced the two new devices and bridge digitizer
  circuits utilizing the unique features of these devices.
  It showed how to remove offset/full-scale errors due to
  excitation currents using the full-scale and zero-scale
  set inputs. Furthermore, part 1 showed pseudo-differential application circuits for directly digitizing 4-and
  6-terminal bridge circuits.
  This article introduces two new applications using the
  2-channel LTC2402. The п¬Ѓrst is a digital cold junction
  compensation circuit for remote measurements. The
  second shows how to digitize an RTD sensor and remove
  voltage drop errors digitally by using the ADC’s second
  channel and underrange capabilities.
  Digital Cold Junction Compensation
  In order to measure absolute temperature with a thermocouple, cold junction compensation must be performed. The LTC2402 enables simple digital cold junction
  compensation. One channel measures the output of the
  thermocouple while the other measures the output of …

Articles

• Download
  No Latency Delta-Sigma ADC Techniques for Optimized Performance &mdash LT Journal
  PDF, 239 Kb, File published: May 1, 2001
  Extract from the document

  DESIGN FEATURES Introduction Product Family Overview Linear Technology’s Delta-Sigma analog-to-digital converter product family
  simplifies a variety of applications.
  The products’ ease-of-use and high
  accuracy without the need for calibration, external clocks or complex
  interfaces enables designers to rethink
  their system architectures.
  Although 24 bits may seem excessive to some, many designers find
  significant advantages with these
  higher resolution converters. One
  such advantage is the elimination of
  front-end amplification. This enables
  direct digitization of many sensors
  while removing problems associated
  with front-end offset and gain errors
  as well as simplifying tare adjustments. One misconception commonly
  solved by designers using the
  LTC2400 family is the relationship
  between speed and resolution. Many
  designers have found that higher
  speed ADCs with averaging do not
  meet the one-shot performance of the
  LTC2400 family. The absolute accuracy of the LTC2400 family is
  demonstrated using a bridge sensor …

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Manufacturer's Classification

• Data Conversion > Analog-to-Digital Converters (ADC) > Precision ADCs (Fs < 10Msps) > Single Channel ADCs