Power Output Select Value ST25R3911B

[GDeto]

Hello Everybody,

Is it possible to control the Power Output of the ST25R3911B?

I am looking options to control the Power Output Programmatically ( Command Send, Register Value Other, I cannot find much information on the Dynamic Power Output DPO ) or by changing the Input Voltage from 5V - 2.4V

What would be a fair range that we could achieve?

Kind Regards.

[GDeto]

Ok, found in the datasheet register 27h RFO Normal Level Definition Register

"It is also possible to switch off certain segments when driving the non-modulated level to reduce the amplitude of the signal on the antenna and/or to reduce the antenna Q factor without making any hardware changes" pg. 15 of DS11793 Rev 4

Thank you.

[Travis Palmer]

​Hello,

Your finding is absolutly right.

Please also have a look at the appnote AN4974 Antenna matching for ST25R3911B/ST25R391x devices, chapter 3.1 Reader output power. According to the appnote you have 3 posibillities to adjust the output power. If you don't want to change the matching network, you change the driver output resistance or change the VSP_RF regulator setting.

If you are using the ST25R3911B Disco board, you could use AAT to switch to a higher matching impedance. Therefore please have a look at appnote

AN4914 Automatic Antenna Tuning (AAT) of ST25R3911B/ST25R391x devices Figure 2 to 10.

Depending on component tolerances trim value 7 or 8 should be the default.

BR Travis