NHS3152 - Powering using NFC

CyrilBZH · ‎03-01-2023

Hello,

I'm using the NHS3152 ADK board.

I want to power the chip just using the NFC, from the datasheet and various posts, the supply voltage is then 1.8V.

Yet when measuring it (VDD on the board), I get at most 0.71V. I tried several NFC reader, it is the best I can get (see picture).

What is the minimum NCF power the reader should have? Do you recommand any in particular?

The programme I'm running set a current sink value of 1.5mA on PIO_3, which should be ok for NFC powering, then a 20uA current from a photodiode is measured using the I2D and place into the NDEFT shared memory. The programme works fine when powered from the LPC-Link2 probe

Thanks

Cyril

patrickgeens · ‎03-02-2023

Hi Cyril,

The power tapped from the NFC field is not routed to the VDDBAT pin. The trick to measure the internal voltage is to put a PIO pin in GPIO mode, set the output high and measure the voltage on the pin with a high-ohmic voltmeter.

We use and test with Identiv uTrust 3700F and Sony RC-S380 readers.
NFC readers field strengths adhere to standards, where USB powered devices typically are on the higher and and phones on the lower end.

The limiting factors in using NFC power are:

- the impedance of power coupling from the NFC front-end and the rest of the chip

- the internal buffer capacitance which provides the charge to keep the internal voltage high during the magnetic field interruptions when the reader or the chip is communicating (every bit is coded as a 3us gap in the field, or the antenna is shorted) External capacitance can be added to PIO pins set to GPIO mode and output high, to couple them to the internal voltage rail. The caps need to be precharged via internal or external pull-up resistor before the output mode is set, otherwise the discharged caps will take the internal voltage down and the system resets.

To make the system working, the internal voltage should stay >= 1.6V, even when there is NFC communication. To be measured via the PIO pin trick.

Key is to make the current consumption as low as possible by using the lowest system clock and switching off unused blocks. The current controlled mode block in the PIO pads is consuming extra current, it could be more efficient to use an external current limiting resistor.

Kind regards,
Patrick

View solution in original post

patrickgeens · ‎03-02-2023

Hi Cyril,

The power tapped from the NFC field is not routed to the VDDBAT pin. The trick to measure the internal voltage is to put a PIO pin in GPIO mode, set the output high and measure the voltage on the pin with a high-ohmic voltmeter.

We use and test with Identiv uTrust 3700F and Sony RC-S380 readers.
NFC readers field strengths adhere to standards, where USB powered devices typically are on the higher and and phones on the lower end.

The limiting factors in using NFC power are:

- the impedance of power coupling from the NFC front-end and the rest of the chip

- the internal buffer capacitance which provides the charge to keep the internal voltage high during the magnetic field interruptions when the reader or the chip is communicating (every bit is coded as a 3us gap in the field, or the antenna is shorted) External capacitance can be added to PIO pins set to GPIO mode and output high, to couple them to the internal voltage rail. The caps need to be precharged via internal or external pull-up resistor before the output mode is set, otherwise the discharged caps will take the internal voltage down and the system resets.

To make the system working, the internal voltage should stay >= 1.6V, even when there is NFC communication. To be measured via the PIO pin trick.

Key is to make the current consumption as low as possible by using the lowest system clock and switching off unused blocks. The current controlled mode block in the PIO pads is consuming extra current, it could be more efficient to use an external current limiting resistor.

Kind regards,
Patrick