U3280M Datasheet, PDF (4/18 Pages) ATMEL Corporation – TRANSPONDER INTERFACE FOR MICROCONTROLLER

Digital Input to Control the
Damping Stage (MOD)
Field Clock
Gap Detect
MOD = 0: coil not damped
V_coil-peak = V_DD × 2 + V_CMS = V_CU
MOD = 1: coil damped
V_coil-peak = V_DD × 2 = V_CD
V_CMS = V_CID: modulation voltage stroke at coil inputs
Note: If the automatic power management is disabled, the internal front-end V_DD is limited at
V_DDC. In this case the value V_DDC must be used in the above formula.
The field clock extractor of the interface makes the field clock available for the microcon-
troller. It can be used to supply timer inputs to synchronize modulation and
demodulation with the field clock.
The transponder interface can also receive data. The base station modulates the data
with short gaps in the field. The gap-detection circuit detects these gaps in the magnetic
field and outputs the NGAP/field signal at the NGAP pin. A high level indicates that a
field is applied at the coil and a low level indicates a gap or that the field is off. The
microcontroller must demodulate the incoming data stream at one of its inputs.
U3280M Signals and Timing
Figure 3. Modulation
MOD
Coil inputs
V_CMS
V_CD
V_CU
Figure 4. GAP and Modulation Timing
Gap detection and battery to field switching
V_FDON
Coil inputs
t _FGAP1
t FGAP0
1. edge used as wakeup signal
NGAP
Field clock FC
Power
management _{Battery supply}
t _BFS ^{Coil supply if automatically power management is enabled}
4 U3280M
V _FDOFF
t_FBS
Battery
supply
4688B–RFID–12/04