MLX90109_06 Datasheet, PDF(6/15 Page) Melexis Microelectronic Systems

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MLX90109_06 Datasheet, PDF (6/15 Pages) Melexis Microelectronic Systems – 125kHz RFID Transceiver

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MLX90109

125kHz RFID Transceiver

7.4 Digital demodulator

The MODE pin allows to define whether the MLX90109 will issue directly the filtered data stream on the

DATA pin (MODE floating), or decode it in Manchester (MODE = VSS) or Biphase (MODE = VDD). In these

two decoding modes, the MLX90109 issues the tag data on the DATA pin at the rising edge of the clock,

which is issued on the CLOCK pin. Both CLOCK and DATA are open drain outputs and require external pull-

up resistors.

SPEED

VSS

4kBaud

MODE

Biphase

(*) Internally strapped to VDD/2

FLOAT (*)

No decoding

VDD

2kBaud

Manchester

7.5 Antenna voltage definition

The MLX90109 is a reader IC working in a frequency range of 100 to 150kHz, and designed for use with a

parallel L-C antenna. This concept requires significantly less current than traditional serial antennas, for

building up the same magnetic field strength.

The voltage on the MODU pin (VMODU) controls the amplitude of the antenna voltage Vant, as follows:

(1)

Vant = VDD âVMODU + VOS

with VOS, the offset relative to the VMODU level.

Note: In order to use the internal driver FET as an ideal current source, the voltage on the coil pin should

remain higher than its saturation voltage (typically 0.5V) for a driver current (Idriver) up to 14mA. As this offset

can be as much as 300mV, VMODU should be higher than 0.8V for a correct operation.

7.6 Power Down mode

By setting VMODU higher than Vpd (preferably to VDD) the MLX90109 goes in power down. The antenna voltage

will fade to 0V. The MLX90109 powers up by pulling VMODU below Vpu.

7.7 Write operation

A sequence of power up / power down periods sets the antenna voltage ON and OFF. This feature allows to

simply make an ON/OFF-keying modulated signal to the transponder.

Typically, VMODU is toggled between VDD and 0.8V. Antenna fade-out is related to the quality factor of the

antenna (Qant) and its start-up takes about 3 carrier periods.

Refer to the section âTypical operating configurationsâ further in this document for more detailed information

and practical hints.

3901090109

Rev 008

Page 6 of 15

Data Sheet

Jun/06

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