topic PN5180 resistor value for RXP and RXN in NFC

PN5180 resistor value for RXP and RXN

emmanuel_sanche — Mon, 21 Oct 2019 16:32:59 GMT

In the document "AN11740 - PN5180 Antenna design guide" section "4.5.1 External Rx components", it mentions that the resistors R1A and R1B are typically in the range of "1...10kΩ". Does this mean 1kΩ to 10kΩ or 1Ω to 10kΩ?

Is there a risk in going outside this range and using a very small resistor value like 100Ω?

Thank you!

Re: PN5180 resistor value for RXP and RXN

Kan_Li — Tue, 22 Oct 2019 19:16:18 GMT

"1...10kΩ" means 1kΩ to 10kΩ, using another value out of this range might cause the dynamic input voltage on RXN and RXP out of spec. Please refer to the following for details.

Have a great day,
Kan

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Re: PN5180 resistor value for RXP and RXN

marcochan — Fri, 08 Nov 2019 07:26:36 GMT

Hi Kan,

The typical value is from 1k to 10kohm, but the final exact value will depend on the final use and the antenna design, right?

We tried to use 1kohm, but we found a problem. Sometimes, the communication distance from our antenna to the bottom of our phone could be just ~3-5mm, but sometimes >15mm. We tried many rounds we also had this symptom. In fact, there is an existing gap ~3mm from our antenna to the top surface of our casing cover. If we just use 1kohm, we worry the sensitivity will not be very stable, the worst case may not communicate.

We also tried to use 100ohm. This value seems without the mentioned symptom. 100ohm can keep the communication distance from the top surface of our casing cover to the bottom of our phones >5mm every time. This also meets our requirement. The basic required communication distance is ~5mm(min) from the top surface of our casing cover.

Do you have any idea or provide more advises for using this value?

Marco

Re: PN5180 resistor value for RXP and RXN

Kan_Li — Mon, 11 Nov 2019 06:08:18 GMT

Hello Marco,

Actually https://www.nxp.com/docs/en/application-note/AN11740.pdf provides the way how to choose the RX resistor value, please kindly refer to 4.5.1 External Rx components for more details.

Hope that helps,

Have a great day,
Kan