EM4450
EM4550
Power-On-Reset (POR)
When the EM4450/4550 with its attached coil enters an electromagnetic field, the built in AC/DC converter will supply the
chip. The DC voltage is monitored and a Reset signal is generated to initialise the logic. The contents of the Control word
and Protection word will be downloaded to enable the functions (INIT). The Power-On-Reset is also provided in order to
make sure that the chip will start issuing correct data. Hysteresis is provided to avoid improper operation at the limit level.
VDD
Vprh
Vprhys
t
Reset
tinit
EM4450 Active
t
Fig. 17
Lock All / Lock Memory Area
The EM4450/4550 can be converted to a Read Only chip or be configured to Read/Write and Read Only Areas by
programming the protection word. This configuration can be locked by write inhibiting the Write Protection Word. Great care
should be taken in doing this operation as there is no further possibility to change the Write Protection Word. The Control
Word can also be protected in the same way thus freezing the operation mode.
Clock Extractor
The Clock extractor will generate a system clock with a frequency corresponding to the frequency of the RF field. The
system clock is used by a sequencer to generate all internal timings.
Data Extractor
The transceiver generated field will be amplitude modulated to transmit data to the EM4450/4550. The Data extractor
demodulates the incoming signal to generate logic levels, and decodes the incoming data.
Modulator
The Data Modulator is driven by the serial data output from the memory which is Manchester encoded. The modulator will
draw a large current from both coil terminals, thus amplitude modulating the RF field according to the memory data.
AC/DC Converter and Voltage Limiter
The AC/DC converter is fully integrated on chip and will extract the power from the incident RF field. The internal DC
voltage will be clamped to avoid high internal DC voltage in strong RF fields.
Special Timings
The Processing Pause Time (tpp), Write Access Time (twa) and EEPROM Write Time (twee) are timings where the
EM4450/4550 is executing internal operations. During these pauses, the RF field will be influenced.
32 32
16 16 (Opt32)
64
32
(Opt64)
(Opt32)
3200
2624
(Opt64)
(Opt32)
RF periods :
(Opt64)
tpp
twa
twee
During Twa and Twee, the signal on the coil is
Same modulation
damped due to a higher current consumption.
as for a normal bit
Fig. 18
10
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