SLOS456N January   2005  – October 2017

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Information
    5. 6.5  LM4040A20I, LM4040B20I Electrical Characteristics
    6. 6.6  LM4040C20I, LM4040D20I Electrical Characteristics
    7. 6.7  LM4040C20Q, LM4040D20Q Electrical Characteristics
    8. 6.8  LM4040A25I, LM4040B25I Electrical Characteristics
    9. 6.9  LM4040C25I, LM4040D25I Electrical Characteristics
    10. 6.10 LM4040C25Q, LM4040D25Q Electrical Characteristics
    11. 6.11 LM4040A30I, LM4040B30I Electrical Characteristics
    12. 6.12 LM4040C30I, LM4040D30I Electrical Characteristics
    13. 6.13 LM4040C30Q, LM4040D30Q Electrical Characteristics
    14. 6.14 LM4040A41I, LM4040B41I Electrical Characteristics
    15. 6.15 LM4040C41I, LM4040D41I Electrical Characteristics
    16. 6.16 LM4040A50I, LM4040B50I Electrical Characteristics
    17. 6.17 LM4040C50I, LM4040D50I Electrical Characteristics
    18. 6.18 LM4040C50Q, LM4040D50Q Electrical Characteristics
    19. 6.19 LM4040A82I, LM4040B82I Electrical Characteristics
    20. 6.20 LM4040C82I, LM4040D82I Electrical Characteristics
    21. 6.21 LM4040A10I, LM4040B10I Electrical Characteristics
    22. 6.22 LM4040C10I, LM4040D10I Electrical Characteristics
    23. 6.23 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shunt Reference
  8. Applications and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 LM4040 Voltage and Accuracy Choice
        2. 8.2.2.2 Cathode and Load Currents
        3. 8.2.2.3 Output Capacitor
        4. 8.2.2.4 SOT-23 Connections
        5. 8.2.2.5 Start-Up Characteristics
      3. 8.2.3 Application Curve
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Related Links
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

Applications and Implementation

NOTE

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.

Application Information

LM4040 is a well known industry standard device used in several applications and end equipment where a reference is required. Below describes this device being used in a data acquisition system. Analog to Digital conversion systems are the most common applications to use LM4040 due to its low reference tolerance which allows high precision in these systems.

Typical Applications

LM4040A LM4040B LM4040C LM4040D ai_data_acq_los456.gif Figure 6. Data-Acquisition Circuit With LM4040x-41

Design Requirements

For this design example, use the parameters listed in Table 1 as the input parameters.

Table 1. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
ADC FSR (Full Scale Range) 4.096
ADC Resolution 12 Bits
Supply Voltage 5 V
Cathode Current (Ik) 100 µA

Detailed Design Procedure

When using LM4040 as a comparator with reference, determine the following:

  • Input voltage range
  • Reference voltage accuracy
  • Output logic input high and low level thresholds
  • Current source resistance

LM4040 Voltage and Accuracy Choice

When using LM4040 as a reference for an ADC, the ADC's FSR (Full Scale Range), Resolution and LSB must be determined. LSB can be determined by:

      LSB=FSR/(2N-1)

With N being the resolution or Number of Bits. FSR and Resolution can be determined by the ADC's datasheet.

Vref can be determined by:

      Vref=FSR+LSB

Though modern data converters use calibration techniques to compensate for any error introduced by a Vref's inaccuracy, it is best to use the highest accuracy available. This is due to errors in the calibration method that may allow some non-linearities introduced by the Vref's initial accuracy.

A good example is the LM4040x-41 that is designed to be a cost-effective voltage reference as required in 12-bit data-acquisition systems. For 12-bit systems operating from 5-V supplies (see Figure 6), the LM4040A-41 (4.096 V, 0.01%) only introduces 4 LSBs (4mV) of possible error in a system that consists of 4096 LSBs.

Cathode and Load Currents

In a typical shunt-regulator configuration (see Figure 7), an external resistor, RS, is connected between the supply and the cathode of the LM4040. RS must be set properly, as it sets the total current available to supply the load (IL) and bias the LM4040 (IZ). In all cases, IZ must stay within a specified range for proper operation of the reference. Taking into consideration one extreme in the variation of the load and supply voltage (maximum IL and minimum VS), RS must be small enough to supply the minimum IZ required for operation of the regulator, as given by data-sheet parameters. At the other extreme, maximum VS and minimum IL, RS must be large enough to limit IZ to less than its maximum-rated value of 15 mA.

RS is calculated according to Equation 1:

Equation 1. LM4040A LM4040B LM4040C LM4040D q_rs_los456.gif
LM4040A LM4040B LM4040C LM4040D ai_shunt_reg_los456.gif Figure 7. Shunt Regulator

Output Capacitor

The LM4040 does not require an output capacitor across cathode and anode for stability. However, if an output bypass capacitor is desired, the LM4040 is designed to be stable with all capacitive loads.

SOT-23 Connections

There is a parasitic Schottky diode connected between pins 2 and 3 of the SOT-23 packaged device. Thus, pin 3 of the SOT-23 package must be left floating or connected to pin 2.

Start-Up Characteristics

In any data conversion system, start-up characteristics are important, as to determine when it is safe begin conversion based upon a steady and settled reference value. As shown in Figure 9 it is best to allow for >20µs from supply start-up to begin conversion.

LM4040A LM4040B LM4040C LM4040D test_circuit_los456.gif Figure 8. Test Circuit

Application Curve

LM4040A LM4040B LM4040C LM4040D g_vz_tr_los456.gif Figure 9. Startup Response