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I have an ADC whose analog input i would like to protect. I have found two papers from Texas Instruments which details on how to do so.

Series Resistor Protection

This is basically adding a series resistor to the ADC input and the input node,

enter image description here

Applying the methods above if my Analog pin limit is 3v and would like to protect until 30v

R = (30 - 3)/ 0.001
R = 27k Ohms

And just by adding a series resistor to the analog pin of the adc it is protected upto 30v. Very simple and very easy to implement.

Thats on paper though, I would like to know if this method is really effective in application. For the experienced please do tell me your experience if this alone can protect you adcs

Flat Clamp Diode Protection

This involves placing a surge protection diode on the ADC input lines shunt the extra current away from the adc.

enter image description here

Using something like TVS0500 as a added layer giving a larger over voltage protection. This how ever is not as easy to implement because its not only that you need 6 (do you even need that many?) of them per differential channel, but a slightly meticulous part selection.

Is it worth the extra way to implement this on actual implementation?

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  • \$\begingroup\$ What are you trying to protect from? ESD? What is the voltage level of your signal that you are sampling? There are TVS parts that are designed to protect differential signals with a single part. Example is the USBLC6-2P6 from ST Micro. \$\endgroup\$
    – BrianB
    May 21, 2020 at 18:31
  • \$\begingroup\$ I use series resistors with clamping diodes to protect 12V zero-crossing comparators from 1200V signals. The only difference between the two methods is whether you are using the internal ESD clamp diodes or external diodes. \$\endgroup\$
    – DKNguyen
    May 21, 2020 at 18:33
  • \$\begingroup\$ @BrianB not ESD just from either careless inputs or "Stress Voltages" where there is unexpected rise of voltage. My vref is 1.5volts but i divide the inputs so that i will be able to read upto 5v. \$\endgroup\$
    – Jake quin
    May 21, 2020 at 18:34
  • \$\begingroup\$ @DKNguyen oh wow thats a large voltage, what configurations was your clamping diodes? Is it like the same as the image or just one diode to ground per ADC channel? \$\endgroup\$
    – Jake quin
    May 21, 2020 at 18:36
  • \$\begingroup\$ @Jakequin My voltages were AC so it is more similar to your bottom image since there is no GND, but mine is a lot more bare bones than the one in your bottom image. I clamped voltage between the end terminals and between each end terminal and the center-tap, and center-tap was connected to cct GND. Note although my comparators could survive 12V, I was only looking for zero-cross which does not require the the signal approach anywhere near 12V so I clamped it to more like 1V. I used diodes that forward bias to clamp rather than TVS but same idea since I chose a low limit , but same idea. \$\endgroup\$
    – DKNguyen
    May 21, 2020 at 18:46

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To protect against careless inputs (as clarified), my recommendation is a combination of series resistance with a shunt TVS diode. Make sure to size the TVS voltage for something greater than your signal (but sufficiently less than IC's max input) and then size the resistor so that it doesn't interfere with the signal being measured but is large enough to handle the current at Vcareless - Vtvs. Also, if you are sampling high-frequency (MHz range and up) signals look for low-capacitance TVS devices.

schematic

simulate this circuit – Schematic created using CircuitLab

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