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

5.1 Using TVS Diodes and Series Resistance for Circuit Protection

A simple way to protect against the EOS event is to add a series limiting resistor to the input, as shown in Figure 5-3. This helps limit the current the op amp sees on the non-inverting node. Select the value of the resistor such that the current is limited to 10mA, and that the current is not so big that the resistor noise affects the circuit.

Now, when the overstress voltage is applied, the 1k resistor limits the voltage and current seen by the device. The current drops to 7.3mA, which is lower than the typical 10mA limit seen on most data sheets. Diode 3 steers the voltage, which is still above the maximum rating, to the power supply. The transient voltage suppressor (TVS) diode is connected to the supply such that the supply voltage is limited to 7V, and the absorption device does not turn on.

EOS Protection with TVS Diodes & Series Resistance Figure 5-3 EOS Protection with TVS Diodes & Series Resistance

A TVS is designed for quick turn on and large power dissipation, making the TVS an option for handling large current and voltage surges that are typical of an ESD/EOS event. Below shows the IV curve of a unidirectional TVS diode curve.

Unidirectional TVS Diode Curve Figure 5-4 Unidirectional TVS Diode Curve

When selecting a TVS diode, understanding the characteristics of the diode is important. VRWM, or the reverse working maximum voltage is the maximum voltage that can be applied to the diode before higher leakage starts to occur. IR is the typical current seen at VRWM. The TVS diode must be selected such that the supply voltage of the device equal to the VRWM of the TVS diode. This allows for minimal leakage during operation.

The peak pulse current corresponds to the maximum current that the TVS diode can handle before failure. The clamping voltage is voltage level the diode regulates to when the clamping voltage sees a transient current.

The breakdown voltage, VBR, is the voltage at which higher leakage current is seen. The value must be chosen to be less than the absolute maximum voltage of the device. This allows the TVS diode to turn on and clamp the supply voltage to a safe level so that the supply never reaches the absolute maximum voltage. However, this is not always possible because there is sometimes no TVS diode that has a VRWM at the operating voltage and a VBR below the absolute maximum rating.

Consider the OPA320. This device has a maximum operating supply voltage of 5.5V and an absolute maximum voltage rating of 6V. If VRWM is set to 5.5V there is never a TVS diode that breaks down before 6V. However, external protection must still be used even though the external protection does not have the preferred characteristics.