U3280M_07 ATMEL [ATMEL Corporation], U3280M_07 Datasheet - Page 7

• Manufacturer Part Number: U3280M_07
• Description: Transponder Interface for Microcontroller
• Manufacturer: ATMEL [ATMEL Corporation]

4.3
4.3.1
4.3.2
4688D–RFID–03/07
Power Supply
Automatic Power Management
Controlling Power Management via the Serial Interface
The U3280M has a power management that handles two power supply sources. Normally, the
IC is supplied by a battery at the V
of the device, the field detection circuit switches automatically from V
The V
the power while the field is modulated by gaps and damping. The EEPROM and the connected
controller always operate with the voltage at the V
Note:
There are different conditions that cause a switch from the battery to field and back from field to
the battery.
The power management switches from battery to field if the rectified voltage (V
inputs becomes higher than the field-on-detection voltage (V
available (0 < V
field-off-detection voltage (V
The field detection stage of the power management has low pass characteristics to suppress
noise. An applied field needs a time delay t
power supply. If the field is removed from the coil, the power management will generate a reset
that can be connected to the microcontroller.
Figure 4-3.
Note:
The automatic mode of the power management can be switched off and on by a command from
the microcontroller. If the automatic mode is switched off, the IC is always supplied by the bat-
tery up to the next power-on reset or to a switch-on command. The power management’s on and
off command must be transferred via the serial interface.
If the power management is switched off and the device is supplied from the battery, it can com-
municate via the field without loading the field. This mode can be used to realize applications
with battery supply if the field is too weak to supply the IC with power.
DD
During field supply the maximum energy from the field is used if a high level is applied at the MOD
input.
The rectified supply voltage from the coil is limited to V
is switched off and V
pin is used to connect a capacitor to smooth the voltage from the rectifier and to buffer
Switch Conditions for Power Management
Batt
< 1.8V). It switches back to battery if the coil voltage becomes lower than the
DD
FDoff
Battery
supply
(V
changes to V
Batt
).
)
Batt
V
pin. If a magnetic field is applied at the LC-resonant circuit
V
Coil
Coil
> V
DDC
< V
.
FDon
FDon
BFS
for t > t
for t > t
(battery-to-field switch delay) to change the
DD
pin.
BFS
BFS
DDC
supply
Field
(2.9V). During field supply, the battery
FDon
), even if no battery voltage is
Batt
to field supply.
coil
U3280M
) from the coil
7