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 How to Test an Op Amp in a System Level Circuit

In many system level designs, testing is performed while op amps are powered off to confirm all components are working. When testing op amps, a voltage or current is applied to the inputs, and the resistance is measured. Depending on the internal diode structure, a wide spectrum of results are viable. The resistance that is being measured is the resistance of the ESD cell(s) inside of the op amp. However, there are a few key parameters that must be followed during a system level test to make sure there is a valid measurement, and that the op amp is not damaged in this test.

The first step is making sure that the device is not powered on. The next step is to ground the supplies of the device. Figure 6-1 shows a valid in circuit test setup for an op amp.

In Circuit Test SetupFigure 6-1 In Circuit Test Setup

Consider the following example: an op amp has a voltage placed on the inputs, while the supplies are left floating. Since the supplies are floating, the voltage has no path to the absorption device. This can lead to unintentionally powering the device on, creating undesired output signals, which can affect other devices in the system. Therefore, best practice is to ground both supplies when verifying device in a system level test. For more details on back-powering an amplifier, see this application note.