topic Re: PN5180 Should I increase or decrease the coupling resistors to increase AGC_VALUE? in NFC

PN5180 Should I increase or decrease the coupling resistors to increase AGC_VALUE?

oferrer — Tue, 27 Feb 2024 11:42:37 GMT

Hi,

I am immersed in the process of optimizing the receiver but I´m a little confused about it.

AN11740 - 4.5.1 External RX components says to increase R1A and R1B if AGC_VALUE is low (<250)

but AN11742 says:

-1.2.4.1 Step 1: Unloaded. The Rx resistor was chosen to be R = 3.0 kΩ. The measurement shows the AGC value of 369 in gear 0, driving ITVDD = 139mA (unloaded). The recommended AGC value is 300, so in this case the Rx resistor could be slightly increased.

-7 Annex, Table 13 "The Rx resistor = 5.1kΩ, so the nominal AGC value unloaded is too low."

-7 Annex ...However, here the AGC values are lower, since a higher Rx coupling resistor has been used."

So, should I increase or decrease the coupling resistors if AGC_VALUE is low (=139)?

Currently, the chosen resistor are 4.7kOhm, as recomended as starting point.

Thanks,

Re: PN5180 Should I increase or decrease the coupling resistors to increase AGC_VALUE?

Fabian_R — Tue, 27 Feb 2024 22:23:47 GMT

Hello sir,

Please keep in mind that these are recommendations that may vary on your design and requirements. These component values should be selected according to the antenna characteristics and your measurements.

Please take a look at our NFC Antenna Tool for a quick recommendation of the components of your antenna.

I also want to recommend to please take a look at our Antenna design video series which shows the iterative process for successfully designing your matching circuit along with the proper calibration and, fine-tuning using NFC Cockpit.

Re: PN5180 Should I increase or decrease the coupling resistors to increase AGC_VALUE?

oferrer — Wed, 28 Feb 2024 01:35:09 GMT

Thanks @Fabian_R for your answer.

My circuit board (prototype) is already printed with pn5180 and a customized antenna on it. NFC Antenna Tool was used for maths (no RX resistor calculated). Now, it's running well.

As i said, i'm optimizing receiver before production. I need to change RX external resistors (1kohm-10kohm) to get optimal AGC_VALUE 600 (ANT1/ANT2 were not connected, pure read mode).

I need to increase AGC_VALUE. That's why my question.

Should I increase or decrease external coupling resistors in order to increase AGC_VALUE?

Is there any contradiction between AN11740 4.5.1 AND (AN11742 Table 5 Example OR AN11742 Table 13 Example)?

Thanks in advance,

Osmany

Re: PN5180 Should I increase or decrease the coupling resistors to increase AGC_VALUE?

Fabian_R — Wed, 28 Feb 2024 23:25:46 GMT

Hello sir,
My recommendation when using DPC is to please follow AN11742 steps, you can start with a 3kΩ and adjust, If the AGC value is too high, increase the Rx resistor value.

Re: PN5180 Should I increase or decrease the coupling resistors to increase AGC_VALUE?

oferrer — Fri, 01 Mar 2024 02:13:14 GMT

Thanks @Fabian_R for your answer,

I had to use an even lower value (2,2kΩ) to get the minimum AGC_VALUE required.

Maybe this low value has to do with the selected high target impedance (battery powered handheld device).

So, i had to decrease coupling resistor in order to increase AGC_VALUE. DPC calibration is now done.

Thanks again.

Osmany