Low power read

[kolwas]

Hello,

I need to make ST25R3916 read as power efficient as possible. I am searching for documentation, but only this voltage regulator I see (0x2C). Is there any option to change field power of NFC to make a read as power efficient as possible? NFC tag will be always on fixed position in fixed range.

Important: we are not talking about detecting card - as capacitance detection is good enough but only on reading the card

[Travis Palmer]

Hello Kolwas,

There are many screws to adjust the output power.

First would be the antenna geometry.

The antenna should be designed in a way, that you have the best coupling in the desired distance.

Also the Q-factor should be properly adjusted to the desired technology and bit rate.

Once done, the best chance to adjust the output power is to select a proper matching impedance.

All information about the above mentioned facts can be found in AN5276.

Since the read range is dependent on reader antenna, tag antenna and coupling, a clear link between read range and matching impedance cannot be done - you will simply have to do try and error to minimize the read range.

br Travis

[kolwas]

I use NFC06A1 board where the settings are tuned but still, it's 500mA. I need to decrease. I changed max bound rate and no change on current. I use ST ST25NFC_Embedded_Lib_ST25R3916_1.4.0, and all settings are changing game on 10% max, so there are very restricted for me.

Could you please give me a hint how to change from software perspective? To just decrease the max NFC field power?

[Ulysses HERNIOSUS]

Hi,

I don't understand your comments on "10% max".

I you want to reduce output power you can play with d_res settings. Inside analogConfigTbl_NFC06A1.c this would be this line here:

0x0028,0x0f,0x00, /* RFO driver resistance Active transmission (d_res) ; Set RFO resistance Active Tx */

Alternatively you could also try to manually set the voltage regulator by adding a line to set the regulator to a low level:

0x002c,0xf8,0x80, /* reg_s=1, manual set to 3.6V */

BR, Ulysses