ZHCSOU3C August   2021  – November 2022 LMH32404

PRODUCTION DATA  

  1. 特性
  2. 应用
  3. 说明
  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 Electrical Characteristics
    6. 6.6 Electrical Characteristics: Logic Threshold and Switching Characteristics
    7. 6.7 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Clamping and Input Protection
      2. 7.3.2 ESD Protection
      3. 7.3.3 Differential Output Stage
    4. 7.4 Device Functional Modes
      1. 7.4.1 Ambient Light Cancellation (ALC) Mode
      2. 7.4.2 Channel Multiplexer Mode
      3. 7.4.3 Low-Power Mode
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Standard TIA Application
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Increase Channel Density for Optical Front-End Systems
        1. 8.2.2.1 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 支持资源
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 术语表
  12. 12Mechanical, Packaging, and Orderable Information

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Clamping and Input Protection

The LMH32404 device is optimized to work with photodiodes (PD) configurations that can source or sink current; however, the LMH32404 is optimized for a sinking current configuration. It is assumed that the LMH32404 device is being used with a PD that is configured with its cathode tied to the amplifier input and the anode tied to a negative supply voltage, unless stated otherwise.

The LMH32404 features two internal clamps, a fast recovery clamp and a soft clamp. The fast recovery clamp is the active clamp when the photodiode is sinking a photocurrent. The soft clamp is the active clamp when the photodiode is sourcing a photocurrent. Stray reflections from nearby objects with high reflectivity can produce large output current pulses from the PD. The linear input range of the LMH32404 is approximately 65 µA. Input currents in excess of the linear current range will cause the internal nodes of the amplifier to saturate, which increases the amplifier recovery time. The end result broadens the output pulse, which leads to blind zones.

To protect against this condition, the LMH32404 features an integrated fast recovery clamp that absorbs and diverts the excess current to the positive supply (VDD1) when the amplifier detects its nodes entering a saturated condition. The integrated clamp minimizes the pulse extension to less than a few nanoseconds for input pulses up to 100 mA. The power-supply pins (VDD1 and VDD2) must have their own bypass capacitors to prevent large input pulses from affecting the differential output stage. The clamp circuitry is active when the amplifier is in standby mode and low-power mode, thereby protecting the TIA input.