SBOS637D October   2016  – June 2019 OPA2325 , OPA325 , OPA4325

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
    1.     Offset Voltage vs Input Common-Mode Voltage
  3. 3 Description
    1.     The OPAx325 as an ADC Driver Amplifier
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions: OPA325
    2.     Pin Functions: OPA2325
    3.     Pin Functions: OPA4325
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information: OPA325
    5. 6.5 Thermal Information: OPA2325
    6. 6.6 Thermal Information: OPA4325
    7. 6.7 Electrical Characteristics: VS = 2.2 V to 5.5 V or ±1.1 V to ±2.75 V
    8. 6.8 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Zero-Crossover Input Stage
      2. 7.3.2 Low Input Offset Voltage
      3. 7.3.3 Input and ESD Protection
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Operating Characteristics
      2. 8.1.2 Basic Amplifier Configurations
      3. 8.1.3 Driving an Analog-to-Digital Converter
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Related Links
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.1 Zero-Crossover Input Stage

Traditional complementary metal-oxide semiconductor (CMOS) rail-to-rail input amplifiers use a complementary input stage: an N-channel input differential pair in parallel with a P-channel differential pair. This configuration results in sudden change in offset voltage when the input stage transitions from the p-channel metal-oxide-semiconductor field effect transistor (PMOS) to the n-type field effect transistor (NMOS), or vice-versa, as shown in Figure 40. This transition results in significant degradation of CMRR and PSRR performance of the amplifier.

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OPA325 OPA2325 OPA4325 ai_offset_cm_volt_bos406.gifFigure 40. Input Common-Mode Voltage vs Input Offset Voltage
(Traditional Rail-to-Rail Input CMOS Amplifiers)

The OPAx325 series of amplifiers includes an internal charge pump that powers the amplifier input stage with an internal supply rail that is higher than the external power supply. The internal supply rail allows a single differential pair to operate and to be linear across the entire input common-mode voltage range, thus eliminating crossover distortion. Rail-to-rail amplifiers that use this technique to eliminate crossover distortion are called zero-crossover amplifiers.

The single differential pair combined with the charge pump allows the OPAx325 to provide superior CMRR across the entire common-mode input range, which extends 100 mV beyond both power-supply rails. Figure 41 shows the input offset voltage versus input common-mode voltage plot for the OPAx325. Note that unlike traditional rail-to-rail CMOS amplifiers, there is no transition region for the OPAx325.

OPA325 OPA2325 OPA4325 C003_SBOS637.pngFigure 41. Offset Voltage vs Common-Mode Voltage (Zero-Crossover)