Scmitt-trigger inputs on nRF52840

[Rulu]

Hello

Does the nRF5280 include Schmitt-trigger inputs on the GPIO pins?

If yes, what are the voltage threasholds for the rising- / falling edges?

(Can't find anything about this in the nRF documentation..)

I'm concerned about slow rising/falling input signals (HW lockup), see link:

https://www.ti.com/lit/an/scba004d/scba004d.pdf

[Rulu]

Hello

One more question related to this: What is the specified maximum rise-/fall time for the inputs? 

[Amanda Hsieh]

Hi, 

The specification for the pads are:
VIH (Input high level) > 70% VDD
VIL (Input low level) < 30% VDD

This means:

• If the Input is above 70% of VDD we guarantee that the input is recognized as a "1".
• If the Input is below 30% of VDD we guarantee that the input is recognized as a "0".

The hysteresis should always be > 20% VDD

We do not have any maximum input rise or fall time specified. If the noise is larger than the hysteresis, there might be glitches into the chip.

-Amanda H.

[Rulu]

Hello

So it means that you don't have schmitt trigger inputs on nRF52840, right?

The reason why I asked about this issue is the risk of 'latch up' ond high current consumption in the device.

Acc to the link from TI stated above (please have a look at this), CMOS inputs should avoid slow rise/fall times.

You say that this is not an issue for the nRF52840, it that right?

[Amanda Hsieh]

Hi Rune, 

Indeed we have schmitt trigger inputs on nRF52840, as can be seen from the hysteresis (>20% VDD). We have picked out some corner cases, and from this it does not seem like we have a problem (Rise and fall time is 5s in the simulation).

-Amanda H.