U2270B_08 Datasheet, PDF (10/18 Pages) ATMEL Corporation – Read/Write Base Station

3.8 Function Table
CFE
Low
Low
High
High
MS
Low
High
Low
High
COIL1
High
Low
COIL2
High
High
OE
Low
High
Output
Enabled
Disabled
STANDBY
Low
High
U2270B
Standby mode
Active
4. Applications
To achieve the system performance, consider the power-supply environment and the mag-
netic-coupling situation.
The selection of the appropriate power-supply operation mode depends on the quality of supply
voltage. If an unregulated supply voltage in the range of V = 7V to 16V is available, the internal
power supply of the U2270B can be used. In this case, standby mode can be used and an exter-
nal low-current microcontroller can be supplied.
If a 5V supply rail is available, it can be used to power the U2270B. In this case, check that the
voltage is noise-free. An external power transistor is not necessary.
The application also depends on the magnetic-coupling situation. The coupling factor mainly
depends on the transmission distance and the antenna coils. The following table lists the appro-
priate application for a given coupling factor. The magnetic coupling factor can be determined
using Atmel^®’s test transponder coil.
Table 4-1. Magnetic Coupling
Magnetic Coupling Factor
k > 3%
k > 1%
k > 0.5%
k > 0.3%
Appropriate Application
Free-running oscillator
Diode feedback
Diode feedback
plus frequency altering
Diode feedback
plus fine frequency tuning
The maximum transmission distance is also influenced by the accuracy of the antenna’s reso-
nance. Therefore, the recommendations given above are proposals only. A good compromise
for the resonance accuracy of the antenna is a value in the range of f_res = 125 kHz ± 3%. Further
details concerning the adequate application and the antenna design is provided in Section
“Antenna Design Hints”.
10 U2270B
4684E–RFID–02/08