CR95HF Calibration Issue

[j23]

Posted on June 19, 2014 at 15:01

Hi,

I have two applications one for the Calibration of CR95HF and one for Tag detection. Before running the Tag detection application Calibration is done and the DAC ref value obtained is saved in a file. The Tag detection application uses the DAC ref value and puts the CR95HF device into IDLE mode with the wakeup event configured as Tag Detection. When a TAG is placed in the proximity area, device wakes up and the application reads the UID. Most of the time everything is working fine. But sometimes, the device is not waking up from IDLE mode, even if TAG is placed in the vicinity area. It may work after some time after some board resets and all. I couldnt find the issue as its not coming regularly. But the issue is a repeating one. One thing I observed is I am getting different DAC Ref value for the same board with antenna connected and without antenna connected. say 0x03 and 0x07. What is the part that antenna does during the calibration procedure.?Also when the Tag detetion application fails, I have seen that the DAC Ref value obtained is the value without antenna, ie 0x03. And When the Tag detection is successful, the Ref value obtained is 0x07. Please help me in finding the issue. Thanks in advance Geethu  #cr95hf #dac #idle

[Anais GALLIGANI · Accepted solution]

Posted on August 28, 2014 at 16:30

Hi,

Concerning the Dac , (see part 5.6.5 of the DS) the user can keep these DacData L and DacDataH values or change them in the change IDLE parameters.

If the difference between DacData L and DacDataH is decrased , the tag detection range is increased. The cons point is that the CR95HF can wake up from the tag detection mode without a tag in the RF field.

The choice of the difference between DacData L and DacDataH values is a trade off between the tag detection range and the reliability of the tag detection. This a user choice.

The lowest power consumption of the CR95HF is the hibernate state. 

In the tag detection state you can decrease the current consumption by increasing the WU period value. The WU period value increases the time between two RF bursts. The AN3433 details the tag detection mode.

You can find more information on the

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/DM00025644.pdf

(

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/DM00025644.pdf

) and

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/application_note/DM00034250.pdf

  (

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/application_note/DM00034250.pdf

)

I hope this is helping,

Have a nice day,

ST NFC /RFID Dynamic tag support