U3280M_07 Datasheet, PDF (6/21 Pages) ATMEL Corporation – Transponder Interface for Microcontroller

4. U3280M Signals and Timing
Figure 4-1. Modulation
MOD
Coil inputs
V_CMS
V_CD
V_CU
Figure 4-2. 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}
V _FDOFF
t_FBS
Battery
supply
4.1 Digital Output of the Gap-detection Stage (NGAP)
NGAP = 0: gap detected/no field
V_coil-peak = V_FDoff
NGAP = 1: field detected
V_coil-peak = V_FDon
Note: No amplifier is used in the gap-detection stage. A digital Schmitt trigger evaluates the rectified and
smoothed coil voltage.
4.2 Wake-up Signal
If a field is applied at the coil of the transponder interface, the microcontroller can be woken up
with the wake-up signal at the NGAP pin. For that purpose, the NGAP pin must be connected to
an interrupt input of the microcontroller. A high level at the NGAP output indicates an applied
field and can be used as a wake-up signal for the microcontroller via an interrupt. The wake-up
signal is generated if power management switches to field supply. The field-detection stage of
the power management has lowpass characteristics to avoid generating wake-up signals and
unnecessary switching between battery and field supply in case of interferences at the coil
inputs.
6 U3280M
4688D–RFID–03/07