TK5552A-PP Atmel, TK5552A-PP Datasheet - Page 7

• Manufacturer Part Number: TK5552A-PP
• Manufacturer: Atmel

Specifications of TK5552A-PP

• Operating Temperature Classification: Commercial
• Lead Free Status / RoHS Status: Compliant

6.3
Figure 6-8.
6.4
Figure 6-9.
4698B–RFID–08/05
Gap detect
Downlink Data Decoding
Behavior of the Real Device
Downlink data decoder
Coil
voltage
Field clock cycles
Downlink Data Decoding Scheme
Ideal and Real Behavior of Signals
RF level decreases to zero immediately
Ideal behavior
t
1
1
The time between two detected gaps is used to encode the information. As soon as a gap is
detected, a counter starts counting the number of field clock cycles until the next gap is
detected. Depending on how many field clocks elapse, the data is regarded as 0 or 1. The
required number of field clocks is shown in
counted clock periods is between 16 and 32, for a valid 1 it is 48 or 64, respectively. If the data
transmission was correct, programming is started and the written block is cycling its data back to
the base station until POR.
The TK5552 detects a gap if the voltage across the coils decreases below the threshold value of
an internal MOS transistor. Until then, the clock pulses are counted. The number given for a
valid “0” or “1” (see
are, however, always more clock pulses being counted than applied by the base station. The
reason for this is that an RF field cannot be switched off immediately. The coil voltage decreases
exponentially. Even if the RF field coming from the base station is switched off, it takes some
time until the voltage across the coils reaches the threshold value of an internal MOS transistor
and the device detects the gap.
Referring to
depend on the application (e.g., field strength, etc.)
Typical time frames are:
t
t
t
Antennas with a high Q-factor require longer times for t
0
1
gap
t
gap
= 180 µs to 400 µs
= 70 µs to 150 µs
= 300 µs to 400 µs
1
t
0
0
Fail
Figure
1
6-9, the device uses t
16
Figure
0
6-8) refers to the actual clock pulses counted by the device. There
32
Gap detect
Coil
voltage
Fail
0 internal
Figure
48
Real behavior
RF level decreases exponentially
t
1 internal
t
1
and t
1
1
6-8. A valid 0 is assumed if the number of
t
1 internal
gap
gap
and shorter time values for t
64
t
0
0
Downlink done
t
0 internal
. The exact values for t
1
TK5552
0
and t
0
and t
1
are
1
.
7