SPVA018 August   2025 LM2904B

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2ESD Overview
    1. 2.1 What is Electrostatic Discharge?
      1. 2.1.1 ESD Cell Robustness in Semiconductors
  6. 3Types of ESD Cells
    1. 3.1 Dual Diode Configuration
      1. 3.1.1 Why Not Always Use Dual Diode Configuration?
    2. 3.2 Bootstrapped Diodes
    3. 3.3 Absorption Devices
      1. 3.3.1 Active Clamps
      2. 3.3.2 GCNMOS Clamps
    4. 3.4 Silicon Controlled Rectifiers
    5. 3.5 CER and ECR NPN Diodes
      1. 3.5.1 Measuring the Response of an ECR and CER ESD Cell
    6. 3.6 Comparison of ESD Cells
  7. 4How to Determine the ESD Structure of the Device from the Data Sheet
  8. 5How to Protect The System from In Circuit ESD/EOS Events
    1. 5.1 Using TVS Diodes and Series Resistance for Circuit Protection
    2. 5.2 Using Schottky Diodes for Circuit Protection
  9. 6How to Test an Op Amp in a System Level Circuit
    1. 6.1 ESD Protection Cell Advancements Over the Years
  10. 7Summary
  11. 8References

3.3.1 Active Clamps

An active clamp is a very common absorption device used in semiconductors. An active clamp is a very large MOS that is in active mode during ESD conditions and is high impedance under normal operating conditions. During an ESD event, the MOS acts as a switch, allowing uniform current flow with a low voltage drop. This device can be edge triggered (dv/dt based) or level triggered. These are most commonly used for protection when the supplies are powered off, but there is still an input signal.

Active Clamp Figure 3-5 Active Clamp

An advantage of this structure is that is has a very low clamping voltage. However, the performance is based on the drain current saturation; as a result, the clamp can take up a very large area. Therefore, a different type of clamp can be more useful if the size of the integrated circuit is a key parameter.