Features
•
•
•
•
•
•
•
•
•
Carrier Frequency f
osc
100 kHz to 150 kHz
Typical Data Rate up to 5 Kbaud at 125 kHz
Suitable for Manchester and Bi-phase Modulation
Power Supply from the Car Battery or from 5V Regulated Voltage
Optimized for Car Immobilizer Applications
Tuning Capability
Microcontroller-compatible Interface
Low Power Consumption in Standby Mode
Power-supply Output for Microcontroller
Applications
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•
•
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Car Immobilizers
Animal Identification
Access Control
Process Control
Read/Write
Base Station
U2270B
1. Description
The U2270B is an IC for IDIC
®
read/write base stations in contactless identification
and immobilizer systems.
The IC incorporates the energy-transfer circuit to supply the transponder. It consists of
an on-chip power supply, an oscillator, and a coil driver optimized for automotive-spe-
cific distances. It also includes all signal-processing circuits which are necessary to
transform the small input signal into a microcontroller-compatible signal.
4684E–RFID–02/08
Figure 1-1.
System Block Diagram
Transponder/TAG
Read/write base station
Osc
Transponder
IC
RF field
typ. 125 kHz
U2270B
NF read channel
Carrier
enable
MCU
Data
output
Unlock
System
Figure 1-2.
Block Diagram
DV
S
V
EXT
V
S
V
Batt
Standby
Power supply
COIL1
=1
MS
CFE
COIL2
Driver
DGND
&
Oscillator
Frequency
adjustment
RF
Amplifier
Input
Lowpass filter
Schmitt trigger
Output
&
HIPASS
GND
OE
2
U2270B
4684E–RFID–02/08
U2270B
2. Pin Configuration
Figure 2-1.
Pinning
GND
OUTPUT
OE
INPUT
MS
CFE
DGND
COIL2
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
HIPASS
RF
VS
STANDBY
VBATT
DVS
VEXT
COIL1
Table 2-1.
Pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Pin Description
Symbol
GND
OUTPUT
OE
INPUT
MS
CFE
DGND
COIL2
COIL1
VEXT
DVS
VBatt
STANDBY
VS
RF
HIPASS
Function
Ground
Data output
Data output enable
Data input
Mode select coil 1: common mode/differential mode
Carrier frequency enable
Driver ground
Coil driver 2
Coil driver 1
External power supply
Driver supply voltage
Battery voltage
Standby input
Internal power supply (5V)
Frequency adjustment
DC decoupling
3
4684E–RFID–02/08
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
Standby
Internal supply
9V
25 kΩ
12 kΩ
6V
PS
COILx
6V
18V
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
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.
5
4684E–RFID–02/08
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