SBOSAF0A april   2023  – august 2023 LMH32401-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Pin Configuration and Functions
  7. 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: Gain = 2 kΩ
    6. 6.6 Electrical Characteristics: Gain = 20 kΩ
    7. 6.7 Electrical Characteristics: Both Gains
    8. 6.8 Electrical Characteristics: Logic Threshold and Switching Characteristics
    9. 6.9 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Switched Gain Transimpedance Amplifier
      2. 7.3.2 Clamping and Input Protection
      3. 7.3.3 ESD Protection
      4. 7.3.4 Differential Output Stage
    4. 7.4 Device Functional Modes
      1. 7.4.1 Ambient Light Cancellation (ALC) Mode
      2. 7.4.2 Power-Down Mode (Multiplexer Mode)
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Development Support
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.2 Detailed Design Procedure

Figure 8-3 shows the test circuit used to measure the LMH32401-Q1 bandwidth and transient pulse response. The voltage source is dc biased close to the input bias voltage of the LMH32401-Q1 (approximately 2.47 V). The internal design of the LMH32401-Q1 is optimized to only source current out of the input pin (pin 3), and all the data shown previously are with the current flowing out of the pin. When the voltage input from the source exceeds 2.47 V, the LMH32401-Q1 input sinks the current. Set VVOD = 0 V when the input must sink the current from the photodiode, or in this case, the voltage source. Set the dc bias so that sum of the input ac and dc component is always greater than the input voltage (2.47 V) when testing the LMH32401-Q1 with a network analyzer or sinusoidal source.

Figure 8-4 and Figure 8-5 shows the bandwidth of the LMH32401-Q1 when the device input is sinking the current. The input current range of the LMH32401-Q1 is reduced when the device input is sinking the current. This effect is seen by the decrease in bandwidth as the output swing increases and is more pronounced in a gain configuration of 20 kΩ. Compare Figure 8-4 with Figure 6-1 and Figure 6-3 to see the effect of current direction and input range in a 2-kΩ gain configuration. In a similar way, compare Figure 8-5 with Figure 6-2 and Figure 6-4 to see the effect of current direction and input range in a gain of 20 kΩ.

Figure 8-6 and Figure 8-7 show the pulsed-output response of the LMH32401-Q1 when the input current is increased past the amplifier linear input range. When the input is sinking current, a soft clamp aids in fast recovery; however, the pulse stretches slightly as the input current overrange increases. Compare Figure 8-6 with Figure 6-21 to see the pulse extension effect in a gain of 2 kΩ. Compare Figure 8-7 with Figure 6-22 to see the pulse extension effect in a gain of 20 kΩ. Knowledge of the pulse extension is used to determine the approximate input current, even under overrange situations that can occur because of the presence of retro-reflectors in the environment. As Figure 7-1 shows, each half of the differential output pulse swings greater than or less than the VOCM voltage, and the resulting maximum differential output swing is 0.75 VPP because VOD is set to 0 V. Consequently, only half of the total ADC range is used in this photodiode configuration.