U2270B_08 Datasheet, PDF (5/18 Pages) ATMEL Corporation – Read/Write Base Station

U2270B
3.2 Operation Modes to Power the U2270B
The following section explains the three different operation modes to power the U2270B.
3.2.1
One-rail Operation
All internal circuits are operated from one 5V power rail (see Figure 3-2). In this case, V_S, V_EXT
and D_VS serve as inputs. V_Batt is not used but should also be connected to that supply rail.
Figure 3-2. One-rail Operation Supply
+5V (stabilized)
+
DV_S V_EXT V_S V_Batt Standby
3.2.2
Two-rail Operation
In this application, the driver voltage, D_VS, and the pre-driver supply, V_EXT, are operated at a
higher voltage than the rest of the circuitry to obtain a higher driver-output swing and thus a
higher magnetic field (see Figure 3-3). V_S is connected to a 5V supply, whereas the driver volt-
ages can be as high as 8V. This operation mode is intended to be used in situations where an
extended communication distance is required.
Figure 3-3. Two-rail Operation Supply
+
+
7V to 8V (stabilized)
5V (stabilized)
DV_S V_EXT V_S V_Batt Standby
3.2.3
Battery-voltage Operation
Using this operation mode, V_S and V_EXT are generated by the internal power supply (see Figure
3-4 on page 6). For this mode, an external voltage regulator is not needed. The IC can be
switched off via the STANDBY pin. V_EXT supplies the base of an external NPN transistor and
external circuits, like a microcontroller (even in standby mode).
Pin V_EXT and V_Batt are overvoltage protected via internal Zener diodes (see Figure 3-1 on page
4).The maximum current into the pins is determined by the maximum power dissipation and the
maximum junction temperature of the IC.
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4684E–RFID–02/08