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LTC2401 LTC2401

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

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  Isolated RS485 Transceiver Breaks Ground Loops &mdash DN228
  PDF, 992 Kb, File published: Apr 2, 2001
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  Isolated RS485 Transceiver Breaks Ground Loops – Design Note 228
  Mitchell Lee Previously, isolation was achieved by using at least three
  optoisolators and a separate isolated power supply. The
  LTC1535 replaces not only the optoisolators, but also the
  power supply, as it includes an on-chip DC/DC converter.
  Other features include selectable driver slew rate to reduce
  EMI and susceptibility to reflections, full-duplex pinout
  and fail-safe detection of open and shorted lines.
  The LTC1535 consists of two separate dice assembled on
  a proprietary, isolated lead frame. The lead frame includes
  integral coupling capacitors that bridge the isolation barrier
  and exhibit 2,500VRMS guaranteed standoff. Data communication takes place via the coupling capacitors, while
  an on-chip, 400kHz push-pull converter sends power to the
  isolated side through a small transformer. Total common
  mode capacitance across the barrier amounts to less than
  20pF, with the transformer accounting for about 16pF of
  the total. Figure 1 shows the complete circuit for a fully
  isolated RS485 port.
  Internally, the two halves of the LTC1535 communicate
  in a ping-pong fashion, first sending transmit data to the
  isolated side and then sending receive data back to the
  nonisolated side. The sampling nature of the internal communications link means that some jitter is introduced into
  the data; this limits the useful baud rate to approximately …

• 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
  Extract from the document

  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 …

• Download
  Resolving Very Small Temperature Differences with the LTC2402 &mdash DN257
  PDF, 75 Kb, File published: May 2, 2001
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  Resolving Very Small Temperature Differences
  with the LTC2402 – Design Note 257
  Derek Redmayne
  The LTC В®2402, a 2-channel 24-bit, No Latency
  Delta-Sigmaв„ў ADC, is well-suited to differential
  temperature sensing using a number of different
  sensors. Extremely good matching between channels
  allows two absolute temperature measurements to
  be compared in order to determine the differential or
  gradient between two points. In the circuits shown
  below, the LTC2402, with averaging, can resolve a
  temperature differential of a few millidegrees, although
  in the case of a single-shot pair of readings, a peak error
  of 0.05В°C is possible. Independently adjustable full-scale
  (FSSET ) and zero-scale (ZSSET ) facilitate 3-or 4-wire
  measurements with platinum RTDs and the automatic
  sequencing of the two channels makes measurements
  across an isolation barrier easier. The no latency feature
  of these ADCs also resolves dilemmas associated
  with pulsed excitation. The use of pulsed excitation
  minimizes or eliminates parasitic thermocouple effects
  that can compromise RTD measurements. In addition,
  pulsed excitation can reduce standby or average power …

Articles

• Download
  1- and 2-Channel, No Latency Delta Sigma , 24-Bit ADCs Easily Digitize a Variety of Sensors &mdash LT Journal
  PDF, 209 Kb, File published: Feb 1, 2000
  Extract from the document

  LINEAR TECHNOLOGY
  FEBRUARY 2000 IN THIS ISSUE…
  COVER ARTICLE
  1-and 2-Channel, No Latency ∆Σ,
  24-Bit ADCs Easily Digitize a
  Variety of Sensors . 1
  Michael K. Mayes and Derek Redmayne Issue Highlights . 2
  LTC® in the News… . 2
  DESIGN FEATURES
  Tiny SOT-23 Step-Down Regulator
  Switches at 1MHz for SpaceCritical Applications . 5 VOLUME X NUMBER 1 1-and 2-Channel,
  No Latency ∆Σ
  ∆Σ, 24-Bit
  ADCs Easily Digitize
  a Variety of Sensors
  by Michael K. Mayes
  and Derek Redmayne Damon Lee 10ВµA Quiescent Current Step-Down
  Regulator Extends Standby Time
  in Handheld Electronics . 8
  Greg Dittmer Beware: Worst-Case Specifications
  Can Be a Reality . 10
  Steve Hobrecht 400MHz Current Feedback Amps
  Offer High Slew Rate without the …

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  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 …

Model Line

Manufacturer's Classification

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