SBOS392H August   2007  – August 2019 REF3312 , REF3318 , REF3320 , REF3325 , REF3330 , REF3333

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      REF3312 in a Single-Supply Signal Chain
      2.      Dropout Voltage vs Load Current
  4. 4 Revision History
  5. 5 Device Comparison
  6. 6 Pin Configuration and Functions
    1. Table 1. Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Parameter Measurement Information
    1. 8.1 Thermal Hysteresis
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Start-Up Time
      2. 9.3.2 Low Temperature Drift
      3. 9.3.3 Power Dissipation
      4. 9.3.4 Noise Performance
    4. 9.4 Device Functional Modes
  10. 10Applications and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Applications
      1. 10.2.1 REF3312 in a Bipolar Signal-Chain Configuration
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
          1. 10.2.1.2.1 Op Amp Level-Shift Design
          2. 10.2.1.2.2 Differential Input Attenuator Design
          3. 10.2.1.2.3 Input Filtering
          4. 10.2.1.2.4 Component Selection
            1. 10.2.1.2.4.1 Voltage References
            2. 10.2.1.2.4.2 Op Amp
          5. 10.2.1.2.5 Input Attenuation and Level Shifting
          6. 10.2.1.2.6 Input Filtering
          7. 10.2.1.2.7 Passive Component Tolerances and Materials
        3. 10.2.1.3 Application Curves
          1. 10.2.1.3.1 DC Performance
          2. 10.2.1.3.2 AC Performance
  11. 11Power-Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Related Links
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Community Resources
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

10.2.1.2.6 Input Filtering

The MSP430 ADC is configured to run from the 1.1-MHz SMCLK with an oversampling rate (OSR) of 256, yielding a sample rate of roughly 4.3 kHz. The input filter cutoff frequency is set to 1 kHz in order to limit the input signal bandwidth, as shown in Equation 17. R8 is 1 kΩ in order to provide isolation from the capacitive load of the low-pass filter, thereby reducing stability concerns.

Equation 17. REF3312 REF3318 REF3320 REF3325 REF3330 REF3333 q_f_a1_plus_2_sbos392.gif

where

  • REF3312 REF3318 REF3320 REF3325 REF3330 REF3333 q_c1_sbos392.gif

Reduce C1 to 150 nF so that it is a standard value.

The A1– input of the delta-sigma (ΔΣ) converter is not buffered, and therefore requires a large capacitor to supply the charge for the internal sampling capacitor. A 47-μF capacitor is selected, resulting in the cutoff frequency illustrated in Equation 18.

Equation 18. REF3312 REF3318 REF3320 REF3325 REF3330 REF3333 q_f_a1_minus_2_sbos392.gif

In applications that cannot tolerate such a low-frequency cutoff, and therefore a long start-up time, buffer the A1– input with another OPA317 to properly drive the ADC input with a lower-input capacitor.