ST25R3916 schematic vs 3916-aat

[mossaab daiki]

what is the correct schematic to refer to for ST25R3916 ? The schematic files downloaded from the st website is different from the schematic proposed in the matching tool for 3916-aat

[Travis Palmer]

Hello Daiki,

the schematic mentioned in the UM2358 Rev 4, page 28/31 represents exactly the proposed and investigated schematics in AN5322 Automatic antenna tuning (AAT) for ST25R3916 and ST25R3920 devices 3.0.

Please be aware that some components are d.n.p. on the discovery board.

br Travis

[mossaab daiki]

Thanks for the answer

what are the default CS and CP values when the board is powered? ( before using the tuning tool)

[mossaab daiki]

Hello, thanks for the answer

I want to double-check the values of the schematic on page 28/31 in UM2358. So, I tested the reader ( when it is On) on the VNA and I can see 13.96M and Q=11-12. I tried to set criteria ( Q, impedance) to get similar values of the schematic with no success with the matching tool. then I would like to double-check some things with you

1- For the antenna in use is it correct to relay data from AN5276 and use them in the matching tool

2-ForThe resonance frequency I get by testing the board on (without a laptop connected), whats the AAT Cs and Cp defaults values ( assuming other numbers are in the schematic on UM2358)

3-the target value for ST25R3916 in terms of Q factor and impedance?

my goal is to increase the Q factor of the actual antenna and as the next step replace it with another one.

Thanks

[Travis Palmer · Accepted solution]

​Hello Daiki,

sorry for the late answer.

1-

Unfortunatly the antenna parameters are not the same for MB1414-A/B and AN5276.

The correct values are:

Antenna Inductance: 848 nH

DC Resistance: 355 mOhm

Parallel Resistance: 2776 Ohm

Self Resonance Freqeuncy: 87 361 012 Hz (87,4MHz)

2-

The default setting depends on the version of board you have.

The MB1414-A which is the first version and has been handed out at some trade shows the default value is:

Reg 0x26 = 0x80

Reg 0x27 = 0x40

The latest version - MB1414-B - has the following default settings for AAT

Reg 0x26 = 0xC5

Reg 0x27 = 0xE3

Please ensure that the driver is turned off (Reg 0x28 = 0xF) when measuring the smith chart.

3-

The plan sounds good. The target Q-Factor is depending on the supported bitrate. Since our Demo should support 848kbps the Q-Factor has been choosen suffciently low. For supporting only 106kbps it could be increased to ~30. The Matching Impedance can be choosen according to the available power budget / maximum current during Tx.

br Travis