U2270B_08 Datasheet, PDF (4/18 Pages) ATMEL Corporation – Read/Write Base Station

3. Functional Description
3.1 Power Supply (PS)
Figure 3-1.
Equivalent Circuit of Power Supply and Antenna Driver
DV_S V_EXT
V_S V_Batt
Internal supply
Standby
9V
25 kΩ
COILx
6V
6V
18V
PS
12 kΩ
DRV
DGND
The U2270B can be operated with one external supply voltage or with two externally-stabilized
supply voltages for an extended driver output voltage or from the 12V battery voltage of a vehi-
cle. The 12V supply capability is achieved via the on-chip power supply (see Figure 3-1). The
power supply provides two different output voltages, V_S and V_EXT.
V_S is the internal power supply voltage for everything except for the driver circuit. Pin VS is used
to connect a block capacitor. V_S can be switched off by the STANDBY pin. In standby mode, the
chip’s power consumption is very low. V_EXT is the supply voltage of the antenna’s pre-driver.
This voltage can also be used to operate external circuits, such as a microcontroller. In conjunc-
tion with an external NPN transistor, it also establishes the supply voltage of the antenna coil
driver, DVS.
4 U2270B
4684E–RFID–02/08