MLX90132 Datasheet, PDF (33/44 Pages) Melexis Microelectronic Systems – 13.56MHz RFID / NFC Transceiver

MLX90132
13.56MHz RFID / NFC Transceiver
8.2 Calibration procedure
The calibration process should be performed with no tag in the environment. It consists of executing a
successive tag detection sequence using a well-known configuration. This to determine the two specific
reference thresholds: DacDataL and DacDataH which will be programmed in the device before entering Tag
Detector Mode. Both thresholds are coded in 6 bits.
During the calibration process, DacDataH value is fixed to 0xFCand the software will vary the DacDataL
value from its minimum value (0x00) to its maximum value (0xFC). At each step, the WUflags byte is read to
know if the HF level is above or below the low threshold (“tag detected flag” set or not).
At the end of the calibration process, the reference level DacDataRef is found and corresponds to the value
of DacDataL for which the wake-up event switches from “WakeUp at the end of MaxSleep cycles” (no tag in
the RF field) to “tag detected”.
To avoid too much sensitivity in the tag detection process, the use of a guard band is recommended. This
value should correspond to at least 2 DAC steps.
Final recommended values with guard band:
 DacDataL= DacDataRef– Guard
 DacDataH= DacDataRef+ Guard
The parameters used to define the tag detection calibration sequence (clocking, set-up time, burst duration,
etc.) must be the same as those used for the future tag detection sequences. MaxSleep has to be set to ‘0’
for the calibration
Another and faster way (binary search: 6 steps) to calibrate the Tag Detector is described in the application
note AN2_MLX90130_32_TagDetector.
9 Field Detector
The MLX90132 embeds a field detector block to measure the field level of an external HF RFID reader. This
is used to be able to monitor the availability of the channel and perform the collision avoidance feature before
switching ON the HF field.
The command “Poll field” can be used to monitor the HF field, the device directly returns a bit indicating that
an HF field has been detected or not. The field detector can also be configured as an option to wake-up from
“Idle” mode, in order to reduce the power consumption as much as possible.
3901090132
Rev. 009
Page 33 of 44
Jan-2014