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 :
Thanks
Hi,
There is a document about Kinetis hardware design Tip & Tricks, please check below link for detailed info:
Kinetis Hardware Design Tip & Tricks
On pins wiTh 5V ToleranT inpuTs, Too large oF a pull-down resisTor can end up wiTh >10ua leakage currenT.
Please see The datasheet for maximum resistance value allowed.
If R1 is too high, the pin level will not drop below VIL which is needed to turn off the p-channel keeper.
R1 must be low enough such that the PFET current will make this IR less than VIL when signal is grounded
Use 20uA to calculate initial R1 value & pick lower value
VDD(V) | Spec VIL(V) | R1(kΩ) max |
1.7 | 0.51 | 25.5 |
2.7 | 0.81 | 40.5 |
2.7 | 0.95 | 47.3 |
3.0 | 1.05 | 52.5 |
3.3 | 1.16 | 57.8 |
3.6 | 1.26 | 63.0 |
If using the internal Pull-up resistor (20kΩ to 50kΩ), Use min Rpu value to calculate initial R1 value & pick lower value:
Wish it helps.
Have a great day,
Ma Hui
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Thanks for your precise response. Just a last thing, I did not find in datasheet given values, can you give me the good datasheet link?
That's a pity.
I checked the MK20 latest datasheet without related info. Sorry for the inconvenience may cause.
Have a great day,
Ma Hui
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Note: If this post answers your question, please click the Correct Answer button. Thank you!
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