ST25R3916 output power configuration

[NKorn.12]

Is there a register to set the outputpower on the ST25R3916 like on a Texas Instruments RFID transceiver? Or is the output power entierly controlled by the DPO?

[Ulysses HERNIOSUS]

Hi NKorn.12,

output power in the 3916 can be regulated by changing the driver resistance (d_res) which disables some of the binary weighted drivers and when using the internal regulator by increasing its drop-out.

DPO is only a secondary function where the MCU can adapt these settings by looking at measured amplitude/phase.

BR, Ulysses

[Travis Palmer · Accepted solution]

Hello NKorn.12,

In general the output power is determined by the load impedance of its load.

The matching network transforms the inductance of the antenna (typically between 0.2uH to 2uH) to a real ohmic impedance. This (matching) impedance of the antenna is then seen as load.

A higher load will cause less current flowing into the matching network and therefore also reduce the power consumption of the whole system.

The AN5276 is guiding you through the design process and give you a good overview of this topic.

Once you have reached your desired output power, you can use DPO to fine tune and reduce the output power dynamically. DPO is based on the before mentioned reduction of the d_res.

There are several appnotes (antenna design, AAT, Thermal considerations, single ended antennas) which are covering this topic more in detail.

BR Travis