AnsweredAssumed Answered

MK20 digital input impedance

Question asked by Rémi Pincent on Jun 19, 2017
Latest reply on Jun 20, 2017 by Hui_Ma

Hello, I'm coming on Kinetis forum, because I got an issue I couldn't explain an MK20DX256, here are messages I've posted about this issue :

I'm coming here, because I did not get any precise anwswers about issue described below.

 

To sum up, I'm using MK20DX256. Recently I got a input impedance problem. When trying to read jack status using this circuit

using a GPIO configured as digital input I read 3.3V and ~1.4V, when jack is connected / disconnected, it should be 3.3V ~ 0.3V. I solved it using a voltage follower.

But from datasheet p 15/16 , I cannot understand why do I have some such leakage current. So, here are my questions :

  • when jack is not connected, voltage output on jack detector (when MK20 not connected) circuit is ~0.3V with an impedance of 60k. If I get 1.4V on input of mk20 when I connect this circuit, that means on MK20 a 100k input impedance is present. Why such an impedance, when in datasheet when Vss <= Vin <= Vil, typical leakage current is 0.002µA?
  • leakage is because of input protection leakage (also refer datasheet p41), but my question is why at Vdd, leakage decreases so much, when in theory it increases with voltage for a diode. Leakage current in this zone is 1µA (max 50µA) << leakage in Vil < Vin < Vdd zone. It must ne because of 5V input protection, but could you detail precisely how it is done internally?

Thanks

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