• Resolved

ISO7840: Absolute Maximum Ratings about "Input voltage"

Part Number: ISO7840

Hi all

Would you mind if we ask ISO7840?

Input voltage of Absolute Maximum Ratings is VCCX + 0.5V.
If voltage applies to INX without VCC1 supply(no power supply), it exeeds Absolute Maximum Ratings.

Does it means there is internal protection diode?
We recognize this value(15mA) is the maximum continuous current for steering-diode(protection diode).
So, if we set the input resistance 1K~5kohm at INX to limit the current for steering-diode, when voltage applies to INX without VCC1 supply(no power supply),
INX is not damaged by the input voltage, right?

Kind regards,

Hirotaka Matsumoto

  • Hi Hirotaka Matumoto,

    We are looking into your query, will get back to you soon.

    thanks,

    Regards
    Tejas
  • The limits of 0.5 V above and below the power rails imply that there are ESD diodes. However, there is no specified limit for the diode current (that 15 mA is for the output current, which flows through the output transistors, which are designed for that).

    If you want to be safe, you have to limit the current to 10 µA or something like that, and you have to ensure that VCC1 does not float up and thus powers the chip.
  • Hirotaka Matsumoto,

    As long as your input signal does not exceed 5V, the ISO7840 will be ok. Putting a resistor in series with the input pins of the device is not a standard set-up but can limit current if you suspect an input signal to occasionally exceed 5V. I would exceed 1k for a series resistor value and also be sure to make sure the resistance will not affect signal speed.