SNAS510S January   2011  – January 2016 LMP90097 , LMP90098 , LMP90099 , LMP90100


  1. Features
  2. Applications
  3. Description
  4. Typical Application Schematic
  5. Revision History
  6. Description (continued)
  7. Pin Configuration and Functions
  8. Specifications
    1. 8.1  Absolute Maximum Ratings
    2. 8.2  ESD Ratings
    3. 8.3  Recommended Operating Conditions
    4. 8.4  Thermal Information
    5. 8.5  Electrical Characteristics
    6. 8.6  SPI Timing Requirements
    7. 8.7  CBS Setup and Hold Timing Requirements
    8. 8.8  SCLK and SDI Timing Requirements
    9. 8.9  SDO Timing Requirements
    10. 8.10 SDO and DRDYB Timing Requirements
    11. 8.11 Typical Characteristics
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 True Continuous Background Calibration
      2. 9.3.2 Continuous Background Sensor Diagnostics
      3. 9.3.3 Flexible Input MUX Channels
      4. 9.3.4 Programmable Gain Amplifiers (FGA and PGA)
      5. 9.3.5 Excitation Current Sources (IB1 and IB2) - LMP90100/LMP90098
      6. 9.3.6 Signal Path
        1. Reference Input (VREF)
        2. Flexible Input MUX (VIN)
        3. Selectable Gains (FGA and PGA)
        4. Buffer (BUFF)
        5. Internal/External CLK Selection
        6. Programmable ODRs
        7. Digital Filter
        8. GPIO (D0-D6)
      7. 9.3.7 Calibration
        1. Background Calibration
          1. Types of Background Calibration
          2. Using Background Calibration
        2. System Calibration
          1. System Calibration Offset Coefficient Determination Mode
          2. System Calibration Gain Coefficient Determination Mode
          3. Post-Calibration Scaling
      8. 9.3.8 Sensor Interface
        1. IB1 and IB2 - Excitation Currents
        2. Burnout Currents
          1. Burnout Current Injection
        3. Sensor Diagnostic Flags
          1. SHORT_THLD_FLAG
          2. RAILS_FLAG
          3. POR_AFT_LST_RD:
          4. OFLO_FLAGS
          5. SAMPLED_CH
      9. 9.3.9 RESET and RESTART
    4. 9.4 Device Functional Modes
      1. 9.4.1 Power Management
      2. 9.4.2 Channels Scan Mode
        1. ScanMode0: Single-Channel Continuous Conversion
        2. ScanMode1: Multiple-Channels Single Scan
        3. ScanMode2: Multiple-Channels Continuous Scan
        4. ScanMode3: Multiple-Channels Continuous Scan with Burnout Currents
    5. 9.5 Programming
      1. 9.5.1  General Rules
      2. 9.5.2  Serial Digital Interface
      3. 9.5.3  Register Address (ADDR)
      4. 9.5.4  Register Read/Write Protocol
      5. 9.5.5  Streaming
      6. 9.5.6  CSB - Chip Select Bar
      7. 9.5.7  SPI Reset
      8. 9.5.8  DRDYB - Data Ready Bar
      9. 9.5.9  DRDYB Case1: Combining SDO/DRDYB with SDO_DRDYB_DRIVER = 0x00
      10. 9.5.10 DRDYB Case2: Combining SDO/DRDYB with SDO_DRDYB_DRIVER = 0x03
      11. 9.5.11 DRDYB Case3: Routing DRDYB to D6
      12. 9.5.12 Data Only Read Transaction
      13. 9.5.13 Cyclic Redundancy Check (CRC)
      14. 9.5.14 Register Read/Write Examples
        1. Writing To Register Examples
        2. Reading From Register Example
      15. 9.5.15 Streaming Examples
        1. Normal Streaming Example
        2. Controlled Streaming Example
    6. 9.6 Register Maps
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Quick Start
      2. 10.1.2 ADC_DOUT Calculation
    2. 10.2 Typical Applications
      1. 10.2.1 3-Wire RTD Using 2 Current Sources
        1. Design Requirements
        2. Detailed Design Procedure
        3. Application Curve
      2. 10.2.2 3-Wire RTD Using 1 Current Source
        1. Design Requirements
        2. Detailed Design Procedure
        3. Application Curve
      3. 10.2.3 Thermocouple with Cold Junction Compensation
        1. Design Requirements
        2. Detailed Design Procedure
      4. 10.2.4 Application Curve
  11. 11Power Supply Recommendations
    1. 11.1 VA and VIO
    2. 11.2 VREF
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Device Nomenclature
        1. Specific Definitions
    2. 13.2 Related Links
    3. 13.3 Community Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

10 Application and Implementation


Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

10.1 Application Information

The LMP90100/LMP90099/LMP90098/LMP90097 are highly integrated, multi-channel, low power 24-bit Sensor AFEs. The devices features a precision, 24-bit Sigma Delta Analog-to-Digital Converter (ADC) with a low-noise programmable gain amplifier and a fully differential high impedance analog input multiplexer. A true continuous background calibration feature allows calibration at all gains and output data rates without interrupting the signal path. The background calibration feature essentially eliminates gain and offset errors across temperature and time, providing measurement accuracy without sacrificing speed and power consumption.

10.1.1 Quick Start

This section shows step-by-step instructions to configure the LMP90xxx to perform a simple DC reading from CH0.

  1. Apply VA = VIO = VREFP1 = 5V, and ground VREFN1
  2. Apply VINP = ¾VREF and VINN = ¼VREF for CH0. Thus, set CH0 = VIN = VINP - VINN = ½VREF (CH0_INPUTCN register)
  3. Set gain = 1 (CH0_CONFIG: GAIN_SEL = 0x0)
  4. Exclude the buffer from the signal path (CH0_CONFIG: BUF_EN = 0)
  5. Set the background to BgcalMode2 (BGCALCN = 0x2)
  6. Select VREF1 (CH0_INPUTCN: VREF_SEL = 0)
  7. To use the internal CLK, set CLK_EXT_DET = 1 and CLK_SEL = 0.
  8. Follow the register read/write protocol (Figure 60) to capture ADC_DOUT from CH0.

10.1.2 ADC_DOUT Calculation

The output code of the LMP90xxx can be calculated as:

Equation 13. LMP90100 LMP90099 LMP90098 LMP90097 30139546.gif
Equation 1 — Output Code

ADC_DOUT is in 24−bit two's complement binary format. The largest positive value is 0x7F_FFFF while the largest negative value is 0x80_0000. In case of an over range the value is automatically clamped to one of these two values.

Figure 77 shows the theoretical output code, ADC_DOUT, vs. analog input voltage, VIN, using the equation above.

LMP90100 LMP90099 LMP90098 LMP90097 30139547.gif Figure 77. ADC_DOUT vs. VIN of a 24-Bit Resolution (VREF = 5.5V, Gain = 1).

10.2 Typical Applications

10.2.1 3-Wire RTD Using 2 Current Sources

LMP90100 LMP90099 LMP90098 LMP90097 30139552.gif Figure 78. Topology 1: 3-Wire RTD Using 2 Current Sources Design Requirements

  • VA = 3V
  • VIO = 3V
  • 3-Wire RTD using 2 current sources Detailed Design Procedure

Figure 78 shows the first topology for a 3-wire resistive temperature detector (RTD) application. Topology 1 uses two excitation current sources, IB1 and IB2, to create a differential voltage across VIN0 and VIN1. As a result of using both IB1 and IB2, only one channel (VIN0-VIN1) needs to be measured. As shown in Equation 14, the equation for this channel is IB1 x (RTD – RCOMP) assuming that RLINE1 = RLINE2. Equation 14 is the VIN equation for Topology 1.

Equation 14. LMP90100 LMP90099 LMP90098 LMP90097 30139595.gif

The PT-100 changes linearly from 100Ω at 0°C to 146.07Ω at 120°C. If desired, choose a suitable compensating resistor (RCOMP) so that VIN can be virtually 0V at any desirable temperature. For example, if RCOMP = 100Ω, then at 0°C, VIN = 0V and thus a higher gain can be used.

The advantage of this circuit is its ratiometric configuration, where VREF = (IB1 + IB2) x (RREF). Equation 15 shows that a ratiometric configuration eliminates IB1 and IB2 from the output equation, thus increasing the overall performance. Equation 15 is for ADC_DOUT showing IB1 and IB2 eimination.

Equation 15. LMP90100 LMP90099 LMP90098 LMP90097 30139555.gif Application Curve

LMP90100 LMP90099 LMP90098 LMP90097 app-cruve-1.gif Figure 79. PT-100 RTD Resistance from –200°C to 850°C

10.2.2 3-Wire RTD Using 1 Current Source

LMP90100 LMP90099 LMP90098 LMP90097 30139596.gif Figure 80. Topology 2: 3-Wire RTD Using 1 Current Source Design Requirements

  • VA = 3V
  • VIO = 3V
  • 3-Wire RTD using 1 current source Detailed Design Procedure

Figure 80 shows the second topology for a 3-wire RTD application. Topology 2 shows the same connection as topology 1, but without IB2. Although this topology eliminates a current source, it requires two channel measurements as shown in Equation 4.

Equation 16. LMP90100 LMP90099 LMP90098 LMP90097 30139597.gif
Equation 4 — VIN Equation for Topology 2 Application Curve

LMP90100 LMP90099 LMP90098 LMP90097 app-cruve-1.gif Figure 81. PT-100 RTD Resistance from –200°C to 850°C

10.2.3 Thermocouple with Cold Junction Compensation

LMP90100 LMP90099 LMP90098 LMP90097 30139599.gif Figure 82. Thermocouple With CJC Design Requirements

  • VA = 5V
  • VIO = 2.7V
  • Thermocouple with Cold Junction Compensation Detailed Design Procedure

The LMP90xxx is also ideal for thermocouple temperature applications. Thermocouples have several advantages that make them popular in many industrial and medical applications. Compare to RTDs, thermistors, and IC sensors, thermocouples are the most rugged, least expensive, and can operate over the largest temperature range.

A thermocouple is a sensor whose junction generates a differential voltage, VIN, that is relative to the temperature difference (Thot – Tcold). Thot is also known as the measuring junction or “hot” junction, which is placed at the measured environment. Tcold is also known as the reference or “cold” junction, which is placed at the measuring system environment.

Because a thermocouple can only measure a temperature difference, it does not have the ability to measure absolute temperature. To determine the absolute temperature of the measured environment (Thot), a technique known as cold junction compensation (CJC) must be used.

In a CJC technique, the “cold” junction temperature, Tcold, is sensed by using an IC temperature sensor, such as the LM94022. The temperature sensor should be placed within close proximity of the reference junction and should have an isothermal connection to the board to minimize any potential temperature gradients.

Once Tcold is obtained, use a standard thermocouple look-up-table to find its equivalent voltage. Next, measure the differential thermocouple voltage and add the equivalent cold junction voltage. Lastly, convert the resulting voltage to temperature using a standard thermocouple look-up-table.

For example, assume Tcold = 20°C. The equivalent voltage from a type K thermocouple look-up-table is 0.798 mV. Next, add the measured differential thermocouple voltage to the Tcold equivalent voltage. For example, if the thermocouple voltage is 4.096 mV, the total would be 0.798 mV + 4.096 mV = 4.894 mV. Referring to the type K thermocouple table gives a temperature of 119.37°C for 4.894 mV.

10.2.4 Application Curve

LMP90100 LMP90099 LMP90098 LMP90097 app-curve-2.gif Figure 83. Thermocouple Output as Function of Temperature