MLX90109
125kHz RFID Transceiver
3901090109 Page 7 of 16 Data Sheet
Rev 011 Jun/12
7.4 Digital demodulator
The MODE pin defines whether the MLX90109 will issue directly the filtered data stream on the DATA pin
(MODE floating), or decode it in Manchester (MODE = V
DD
) or Biphase (MODE = V
SS
). 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.
(*)
4kBaud - 2kBaud
Biphase No decoding Manchester
(*) Internally strapped to V
DD
/2
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 (V
MODU
) controls the amplitude of the antenna voltage V
ant
, as follows:
(1)
OSMODUDDant
VVVV
with V
OS
, the offset relative to the V
MODU
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 (I
driver
) up to 14mA. As this offset
can be as much as 300mV, V
MODU
should be higher than 0.8V for a correct operation.
7.6 Power Down mode
By setting V
MODU
higher than V
pd
(preferably to V
DD
) the MLX90109 goes in power down. The antenna voltage
will fade to 0V. The MLX90109 powers up by pulling V
MODU
below V
pu
.
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, V
MODU
is toggled between VDD and 0.8V. Antenna fade-out is related to the quality factor of the
antenna (Q
ant
) and its start-up takes about 3 carrier periods.
Refer to the section “Typical operating configurations” further in this document for more detailed information
and practical hints.
