SNOAA91 may   2023 TLV1812 , TLV1851 , TLV7011

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Input Types
    1. 2.1 Classic Bipolar Inputs
    2. 2.2 ESD Protected Inputs
    3. 2.3 "Fail-Safe" and "Fault Tolerant" Inputs
      1. 2.3.1 LM339 Family - The Original "Fail-Safe" Input
      2. 2.3.2 Modern "Fail-Safe" Inputs
    4. 2.4 "Over-the-Rail" Inputs
  6. 3Identifying The Difference Between The Input Types
    1. 3.1 Older Bipolar Device Inputs
    2. 3.2 Identifying ESD Clamped Inputs
    3. 3.3 Identifying "Failsafe" or "Over-The-Rail" Inputs
  7. 4Precautions for "Failsafe" and "Over-The-Rail" Inputs
  8. 5Negative Input Voltages
  9. 6Input Types Comparison Table
  10. 7Summary
  11. 8References

4 Precautions for "Failsafe" and "Over-The-Rail" Inputs

The non-ESD clamped inputs do not have upper clamps to limit positive voltage excursions, so it is possible to drive the inputs higher than the positive maximum rated input voltage, possibly up to the device breakdown point (and possible damage).

Many customer designs simply place a current limiting resistor in series with the input, and rely on the internal ESD clamp diode to clamp the input voltage to the supply.

This can be an issue if a new fail-safe type input device is replacing a existing conventional ESD clamped comparator with a series resistor in an existing design.

GUID-20230215-SS0I-CSNL-FR5L-Z27TXL4JJLQR-low.svg Figure 4-1 Recommended Input Voltage Zener Clamp

External clamping, such as a Zener or TVS to ground, or a Shottky diode to the positive supply, is required to prevent exceeding the maximum input voltage. Figure 4-1 shows adding a zener diode (or TVS) to limit the maximum applied input voltage. TI recommends a clamp current of 1 mA or less.