How to reduce the current of ST25R3920B

[zhangxixun]

Hi all，

I now use ST25R3920B as a card reader on the official nucleo nfc08A1 of ST to read cards. However, I found that when the card was detected by 3920B, the current increased to 300mA, but the maximum current borne by PCB was 350mA.

Can I reduce the current and how should I operate the configuration software code?

[zhangxixun]

At the same time, I would like to ask, what is the current of 3920B in normal operation?

[Ulysses HERNIOSUS]

Hi,

the current with field on depends on:

1. Matching impedance
2. Output driver resistance (can be influenced from software by d_res bits)
3. Driver voltage (can be influenced from software by reg_s and rege settings.

There is no given current for normal operation. In the electrical characteristics of the datasheet you will find max allowed value for current.

You can reduce the current statically by the three means above. Additionally you can also try to define a DPO setting where the amplitude measured on RFi is used to define a reduction of regulator settings and/or increase the driver resistance.

BR, Ulysses

[zhangxixun]

Hi Ulysses,

thanks for your reply. I see that it is described in DS that the Vdd_rf regulator contains a current limiter. What is the meaning described in this picture? Means: "When the regulator is set to any regulated value, the current limiter limits the current to 350mArms"?