U2270B_08 Datasheet, PDF (11/18 Pages) ATMEL Corporation – Read/Write Base Station

U2270B
The application of the U2270B includes the two capacitors C_IN and C_HP whose values are lin-
early dependent on the transponder’s data rate. The following table gives the appropriate values
for the most common data rates. The values are valid for Manchester and bi-phase code.
Table 4-2. Recommended Capacitor Values
Data Rate f = 125 kHz
f / 32 = 3.9 Kbits/s
Input Capacitor (C_IN)
680 pF
f / 64 = 1.95 Kbits/s
1.2 nF
Decoupling Capacitor (C_HP)
100 nF
220 nF
The following applications are typical examples. The values of C_IN and C_HP correspond to the
transponder’s data rate only. The arrangement to fit the magnetic-coupling situation is also inde-
pendent of other design issues except for one constellation. This constellation, consisting of
diode feedback plus fine frequency tuning together with the two-rail power supply, should be
used if the transmission distance is d ≈ 10 cm.
4.1 Application 1
Application using few external components. This application is for intense magnetic coupling
only.
Figure 4-1. Application Circuit 1
5V
47 nF
+
47 µF
470 kΩ
C_IN
1N4148
R 1.35 mH
1.5 nF
1.2 nF
110 kΩ
V_Batt
V_EXT V_S
DV_S
RF
U2270B _MS
INPUT
CFE
OE
STANDBY
OUTPUT
COIL1
HIPASS
C_HP
COIL2
DGND GND
V_DD
Micro-
controller
V_SS
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4684E–RFID–02/08