10

4684E–RFID–02/08

U2270B

3.8

Function Table

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

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

details concerning the adequate application and the antenna design is provided in Section

“Antenna Design Hints”.

CFE

MS

COIL1

COIL2

Low

Low

High

High

Low

High

Low

High

High

Low

High

High

OE

Output

STANDBY

U2270B

Low

Enabled

Low

Standby mode

High

Disabled

High

Active

Table 4-1.

Magnetic Coupling

Magnetic Coupling Factor

Appropriate Application

k > 3%

Free-running oscillator

k > 1%

Diode feedback

k > 0.5%

Diode feedback

plus frequency altering

k > 0.3%

Diode feedback

plus fine frequency tuning