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

6.1 ESD Protection Cell Advancements Over the Years

Like any semiconductor technology, great advancements have been made over the decades. ESD protection was not a standard part of the op amp design until the 1990s. Thus, many devices from the 1970s and 1980s possibly does not have ESD cells! These older generation op amps have larger geometry devices so the op amps are inherently more robust against ESD damage. However, if ESD protection is the main concern, review the ESD specification and confirm that the device meets your requirement.

Some op amps have been updated over the years, moving to newer processes and technologies. During this modernization, ESD cells were added or changed. Since the topology has changed, the inherent resistance from the diode structure is also different. This can lead to false failures in a system level board test.

Most diodes follow the same general IV curve, as seen below. Usually, the forward bias voltage is around 0.7V for silicon diodes. However, all diodes vary, and updating the ESD cells can change the IV curve characteristics of ESD cells inside an op amp.

I/V Curve of Diode Figure 6-2 I/V Curve of Diode

One example of an op amp with updated ESD structure is the OPAx130 family. Table 6-1 shows the IV measurement differences of the op amp with the original ESD design, and the updated design. In this setup, 100µA is forced into the pin, and the voltage is measured.

Table 6-1 OPA2130 Input and Output to VCC Measurements
Pin to V+ Voltage Measurements Pin 1 to Pin 8 (OUT A to V+) Pin 2 to Pin 8 (-IN A to V+) Pin 3 to Pin 8 (+IN A to V+) Pin 5 to Pin 8 (+IN B to V+) Pin 6 to Pin 8 (-IN B to V+) Pin 7 to Pin 8 (OUT B to V+)
OPA2130 Original Design 0.609678V 0.699382V 0.668025V 0.670190V 0.668482V 0.610322V
OPA2130 Redesign 0.688358V 0.709175V 0.709203V 0.709174V 0.709235V 0.688545V

Note that while the diode structure of a device can change, there is no change in behavior of the device. This is because these protection structures are only triggered during abnormal device operation, such as ESD.