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NTAG5 Boost (NTA53321G0FTTZ) – NFC stops working when external power is applied

Hi everyone,

I’m working on a custom PCB that includes the NTAG5 Boost (part number NTA53321G0FTTZ).
I’m not using Energy Harvesting – instead, the board is powered via a cable.

The issue:

When the board is not powered, I can scan, read, and write the NTAG5 using my phone’s NFC with no problem.
As soon as I apply external power to my board, the NTAG5 completely disappears from NFC – it won’t scan, read, or be detected at all.
Powering off the board immediately makes it scannable again.

Intended use case:
I want to use the NTAG5 in I²C Master mode (NFC to I²C bridge).
From the datasheet, I understand that the Arbiter may control NFC/I²C access, and I’m wondering if it’s blocking NFC field access when the I²C side is active.

What I’ve tried:

Verified my wiring – SDA/SCL lines are connected with ~3.3 kΩ pull-ups.
No Energy Harvesting pins are connected.
Tried different CONFIG_1 settings (USE_CASE_CONF = I²C Master, PT_TRANSFER_DIR = NFC → I²C).
Confirmed configuration values are written correctly.
Checked that the ED/PWM0 pin is not intentionally driven low (but I’m unsure if it needs a pull-up in my case).

My suspicion:
It could be a configuration or default power-on setting issue.
Possibly the Arbiter or ED pin state is blocking NFC when powered.
Or the NTAG5 defaults to I²C slave behavior and “waits” for I²C, effectively ignoring NFC.

Questions:

Has anyone seen similar behavior where the NTAG5 stops responding to NFC when VCC is applied?
Do I need to explicitly configure the ED/PWM0 pin or Arbiter mode after power-up?
Could the absence of a pull-up on ED cause this?
Any known gotchas when using I²C Master mode without a host MCU controlling the NTAG5?

Any insights or experiences would be greatly appreciated – I’ve been stuck on this for a while.

Thanks!

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Re: NTAG5 Boost (NTA53321G0FTTZ) – NFC stops working when external power is applied

Hello @eleng

Since you are using a small antenna, Active communication mode (NTAG 5 boost Data Sheet, Section 8.2.2) is recommended. However, this configuration requires the IC to be Vcc and Vcc_tx supplied.

Please, make sure you are supplying Vcc_tx and follow the recommendations described in Antenna design guide for NTAG 5 Boost.

Since this is the same topic that you submitted in the internal ticket, we will continue the communication in that ticket.

Regards,
Eduardo.