Scmitt-trigger inputs on nRF52840

RE: Scmitt-trigger inputs on nRF52840

Amanda Hsieh — Fri, 07 Feb 2020 08:11:13 GMT

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.

RE: Scmitt-trigger inputs on nRF52840

Rulu — Thu, 06 Feb 2020 12:00:38 GMT

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?

RE: Scmitt-trigger inputs on nRF52840

Amanda Hsieh — Thu, 06 Feb 2020 11:42:17 GMT

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.

RE: Scmitt-trigger inputs on nRF52840

Rulu — Mon, 03 Feb 2020 10:05:03 GMT

Hello

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

RE: Scmitt-trigger inputs on nRF52840

Amanda Hsieh — Thu, 30 Jan 2020 12:15:16 GMT

Hi,

I am checking with the internal and will be back soon.

-Amanda H.