PN7150 LPCD

[deborah_linzi]

Hello,

I'm trying to test the LPCD functionality following the AN11757 on two different boards, one is a custom board and the other is the nxp evalboard OM5578/PN7150S.

I see two different behaviours, on the eval board, approaching a piece of metal the  number reported on the consolle (as per par 4.3.2, the two last bytes) increase while on the custom board it decrease. I can't figure out the reason for that, anyone can help me in understanding this effect?

Thanks and best regards

Deborah

[Kan_Li]

Hello @deborah_linzi ,

How about the antenna tuning on your custom board? Did you follow the steps in https://www.nxp.com/docs/en/application-note/AN11755.pdf ? Please kindly clarify.

Have a great day,
Kan

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[deborah_linzi]

Hello Kan,

Yes I followed the AN11755 and measuring the impedence with a VNA I see something like 20 ohms with very low imaginary part. 

I did the same measurements on two eval board and the impedence is very different form the expected one.

Anyhow, I was able to get it working, at least it detect the card.

If you don't mind, for my next step, I have another question. When a card is approaching, the reader, thanks to the LPCD, reads the card than it assert the IRQ pin so that the host can get the data. Do you think there is any way to get the IRQ asserted when approaching for istance a piece of metal instead of a tag? The idea is to use the PN7150 to wakeup the host when something is appoachind. Of course it must be something affecting the electromagnetic field, that's why I was referring to a piece of metal.

Connecting a loop to the oscilloscope I see that the reader detects the metal and start trying to read but the IRQ pin doesn't move. That's is normal but is there any way to set the device so that the IRQ will be asserted regardless of what is approaching?

many thanks

Deborah

[Kan_Li]

Hi @deborah_linzi ,

I am sorry, but PN7150 doesn't support this feature. The IRQ pin is asserted when a card is detected , otherwise it would wake up the host more than expected, not good for LPCD mode to save power.

Hope that makes sense,

Have a great day,
Kan

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