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Reader IC U2270B

VBatt

Reader IC U2270B
VBatt
OSC Enable
COIL1
Driver
Oscillator
Power supply
Standby
COIL2
U2270B
Output Input NF read channel CODE
Ouput Enable
The U2270B serves as interface between the transponder and the microcontroller that compares the received data. This interface operates bidirectional. One direction is the energy transfer from the reader to the transponder. The reader creates a magnetic field via a reader air coil. This coil is operated by a special driver circuit. The driver consists of two output stages that can be operated in common or in differential mode via the Pin MS. Using this feature, the user is flexible in the design of the antenna. The driver is controlled by an on-chip oscillator. The operating frequency is programmed by an external resistor. This enables the user to externally adjust the frequency to the relevant circumstances. This feature is important to compensate frequency tolerances of the antenna and the transponder. The oscillator can be disabled through pin CFE to enable read-write operation.
The other direction is the data transfer from the transponder to the microcontroller. The transponder modulates the magnetic field with its internal data. This leads to a tiny voltage modulation at the reader coil. Via a rectifier, this signal is fed into the input pin of the reader IC. The NF read channel amplifies and conditions the signal to convert it to the appropriate digital output data. The gain of the amplifier can be programmed through Pin GAIN to adopt to the relevant reading distance. An opencollector output serves as interface to the connected controller. With a logic signal at Pin OE, the data output can be disabled. The reader IC also incorporates an internal power supply. This enables the user to operate the system from a 12-V supply but also from an existing 5-V supply rail. Via the Pin Standby, the U2270B can be set to power-down mode where the supply current is very low.
Extended Reading Range with Large Reader Antennas with U2270B
12 mm a (mm) d (mm)
0.6 0.4 0.2 0.0 30 35 40 45 50 55 60 65 70 75 80 a, r ( mm ) 85 90 95 100 105 110
r (mm)
Figure 1. Coupling factor vs. coil radius and distance
Calculation Maximal U2270B output current (see chapter "Antenna Design Hints") V DS + VEXT + 8 V V DRVpp + 14.8 Vpp 4 V DRVss + p V DRVpp + 18.8 V V DS + VEXT + 8 V V DRVpp + 14.8 Vpp 4 V DRVss + p Q R + 12 V DRVpp + 18.8 V
V DRVss + 400 mAss
V Rss + VDRVss XL +
VRss + 565 W IDRVss 2 XL + 719 mH p f0
R5 360 U2 7808 C5 47u BR6 5 6 10 11 12 13 14 C3 1n 8 U1 BR3 BR4 BR2
R42 MS CFE VEXT DVS VBATT STANDBY VS COIL2 GND OE OUTPUT 2
R10 4k7
C8 47u
C9 47u
R3 4k7
COIL2
COIL1
R6 100
COIL1 INPUT
DGND GAIN
GND D1 D2 1N4148 C1 680p R1 4k7 R8 75k R9 100k 1N4148 D3 1N4148
D4 1N4148 D5 1N4148 C6 4n7
C2 1n5
R2 470k
Figure 3. Application schematic
Distance Measurements Using Application Kit TMEB8704
(Best case results @ 25 degrees) Transponder Type Reading Distance without Autotuning RF / 32 TK5530 TK5551 TK5552 TK5561 8 cm 7.5 cm 8 cm 6.5 cm 8.5 cm 7.0 cm RF / 64 with Autotuning RF / 32 8 cm 8 cm 8 cm 7 cm 8.5 cm 7 cm 6.5 cm 11 cm 7 cm RF / 64 Writing Distance
Order address of the transceiver coil: Part no. V-31013-30001
Company Wagner Elektrogeraete GmbH Sulzbacher Str. 4-8 71577 Grosserlach Germany
TMEB8704 Description
Programmable Transponder IC / with Interface to an Active RF / IR Channel
System Solution for Immobilizer in Combination with RKE
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Lights
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