Hi, i am investigating the maximum power with which i could feed the ST25R3916 disco board.

[AKril.1]

What is the maximum power that i can use? Which pin can i use to feed the board with external power? What is the max power that is transmitted to the RF circuit of the board? Which are the limitations in power?

[Ulysses HERNIOSUS]

Hi AKril.1,

from ST25R3916 chip perspective please see symbols VDD, VDD_TX, IVDD_EXT and IVDD_LDO in Absolute Maximum Ratings.

From MB1414 board please consult UM2358 chapter 5 for details on this board. If you set the Switch to 5V supply you can attach on pin VBUS your own supply, just bend/cut the pin.

However even when supplying more voltage the actual output power is determined by the antenna impedance, i.e. geometry, matching, etc.

If necessary there is also solder option to use voltage regulator bypass mode.

Please beware that when using bypass mode the AM modulation depth must be resistively regulated in software by setting d_res bits.

Regards, Ulysses

[AKril.1]

Thank you.

Could you tell me which is the impedance that is seen by the antenna?

Also, what is the current limitation of the board( the max current that i can apply to the board)?

[Ulysses HERNIOSUS]

Hi AKril.1,

AN5276 talks about the measurements of antenna parameters and meaningful targets of impedance an Q-factor. AFAIK the impedance of the MB1414 is not fixed but can be changed within certain limits by means of AAT / mounted Vari-caps.

As to the available impedance limits on the board I will forward to our hardware engineers.

Regards, Ulysses

[Ulysses HERNIOSUS · Accepted solution]

Hi AKril.1,

I got some feedback:

Impedance is a physical parameter of the antenna + matching circuit. Together with the output resistance of the driver and the supply voltage it causes a resulting current. Please see AN5584 and its chapter 4.3 and 4.4 for basic formulas on power-dissipation. They should give you a good idea about the correlations.

I didn't find data on various Varicap values of the board but they could be obtained by varying the AAT values in GUI and measuring on an externally supplied MB1414 (please make sure to stay within limits of parameters in  Absolute Maximum Ratings: <6V, <350/500mA, etc.).

Regards, Ulysses

Best Regards, Ulysses