ST25R3916B Code that controls RF power

[he2]

您好

我们使用NFC08A1开发板做NFC识别时，功率无法达到介绍中的1.7W。

开始以为是VDD_RF的电压偏低，然后控制寄存器2C的rege将VDD_RF的电压设置为5.1V，使用B区域寄存器2C和万用表读取都没达到5.1V，测量到的最高电压只有4.9V。而且运行直接命令开场后电压降为4.6V。开发板的最高电流只有100mA。排查过供电电源没有功率受限的问题。

想问下如何提高功率，期待获取到贵公司的指导。

 

Hello.

When we use the NFC08A1 development board for NFC identification, the power cannot reach the 1.7W in the introduction.

At first, it was thought that the voltage of VDD_RF was low, and then the rege of the control register 2C set the voltage of VDD_RF to 5.1V, but the reading of the B-zone register 2C and multimeter did not reach 5.1V, and the highest voltage measured was only 4.9V. And the voltage drops to 4.6V after running the direct command. The maximum current of the development board is only 100mA. Checked that the power supply is not limited.

I would like to ask how to improve the power and look forward to getting your guidance.

[he2]

VDD_RF外接VDD，没开场时还有5V，开场后会掉到4.6V。有知道啥原因的嘛

VDD_RF external VDD, there is 5V before opening, and it will drop to 4.6V after opening. I don't know why

[Ulysses HERNIOSUS]

Hi he2,

output power is a function of antenna/matching impedance. Please see https://community.st.com/t5/st25-nfc-rfid-tags-and-readers/st25r3916-output-power-configuration/m-p/112414 where some details are explained.

BR, Ulysses

[he2]

I modified the RFO drive impedance of 0x28 according to the method of document AN5276, and the current did not increase. Then I increased the VDD voltage to 5.4V, and the VDD_RF voltage to 4.8V after the opening, and the current was only increased by 6mA. Is there any other way to increase the power?

[Ulysses HERNIOSUS]

Hi he2,

 

Output power depends according AN5276 on:

1. impedance matching
2. antenna driver output resistance (register 0x28)
3. chip internal regulator voltage

 

If you have let's say a matching impedance of 50 ohms then you are by that already limited to at most 100mA (assuming 5V supply). Slightly increasing supply will only give a proportional increase. Also playing with the output driver resistance cannot do much.

If you really need to go high power you need to work on antenna and matching.

BR, Ulysses

[liaifat85]

You mentioned that the maximum current draw of the board is only 100mA. This is insufficient to achieve the 1.7W power output. It needs a higher current (around 333mA).