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Original question:

UCC5870-Q1: Protecting AI input from high voltage

UCC5870-Q1: AI input clamp

GS
Prodigy 30 points
Part Number: UCC5870-Q1

I would like to ask a similar question to what has been already brought up here, but the answer was provided by email to someone else.

I'm planning to measure some secondary side voltages, but there might be an event that the measured voltage is higher that what the reference allows. What is the recommended protection method? Is just a series resistance enough, or should I implement external clamping diode to VREF? Or is there some other method that I should use?

What about the case when the input voltage is present, but the secondary supply to UCC5870-Q1 has been cut off completely?

  • 0
    TI__Guru**** 189401 points

    Hi,

    Our office is closed for the US Memorial Day holiday. My colleague will get back to you mid next week. Thanks for your patience!

  • 0
    TI__Prodigy 255 points

    Hi, 

    Thanks a lot for your question. Before logging out for holiday, I can help answer your questions. 

    1) Measurement ranges of AI pins are 0-3.6V. Voltages high than 3.6V will saturate the measurement results, i.e., voltage higher than 3.6V will always be read as 3.6V. 

    2) AI pin voltages should not be higher than VREF since there is a protection diode between AI pins and VREF. 

    3) If there are cases that AI pin voltages are higher than VREF and those cases cannot be avoided, then the current flowing into the AI pins should be limited.  Limiting the current into AI pin to less than ~1mA should protect the device. You can use any methods preferred, series resistance, TVS diode, etc. to limit the current into the AI pins. 

    4) If the secondary supply is cut off, VREF will be 0V. In this case, if there are voltages at AI pin, you also need to limit the current into the AI pins to be less than ~1mA to protect the device. 

    Hope this helps.