ATMEL U2270B User Manual

Features

•

Carrier Frequency f

•

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 5-V Regulated Voltage

•

Optimized for Car Immobilizer Applications

•

Tuning Capability

•

Microcontroller-compatible Interface

•

Low Power Consumption in Standby Mode

•

Power-supply Output for Microcontroller

100 kHz to 150 kHz

osc

Read/Write Base Station

Applications

•

Car Immobilizers

•

Animal Identification

•

Access Control

•

Process Control

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-specific distances. It also includes all signal-processing circuits which are necessary to transform the small input signal into a microcontroller-compatible signal.

Figure 1-1. System Block Diagram

Transponder/TAG

Transponder

RF field

typ. 125 kHz

Read/write base station

Osc

U2270B

NF read channel

Carrier

enable

Data output

MCU

Unlock

System

U2270B

Rev. 4684B–RFID–09/05

Figure 1-2. Block Diagram

COIL1

COIL2

DGND

Input

Driver

Lowpass filter

EXT

= 1

Amplifier

Schmitt trigger

HIPASS OEGND

Power supply

Batt

Oscillator

Frequency

adjustment

Standby

CFE

Output

U2270B

4684B–RFID–09/05

2. Pin Configuration

Figure 2-1. Pinning

Table 2-1. Pin Description

Pin Symbol Function

1 GND Ground 2 OUTPUT Data output 3 OE Data output enable 4 INPUT Data input 5 MS Mode select coil 1: common mode/differential mode 6 CFE Carrier frequency enable 7 DGND Driver ground 8 COIL2 Coil driver 2

9 COIL1 Coil driver 1 10 VEXT External power supply 11 DVS Driver supply voltage 12 VBatt Battery voltage 13 STANDBY Standby input 14 VS Internal power supply (5V) 15 RF Frequency adjustment 16 HIPASS DC decoupling

GND

OUTPUT

INPUT

CFE DGND COIL2

U2270B

HIPASS

STANDBY

VBATT

DVS

VEXT

COIL1

4684B–RFID–09/05

3. Functional Description

3.1 Power Supply (PS)

Figure 3-1. Equivalent Circuit of Power Supply and Antenna Driver

EXT

internal supply

9 V

6 V 6 V 18 V

Batt

Standby

25 kΩ

12 kΩ

COILx

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 12-V battery voltage of a vehicle. The 12-V supply capability is achieved via the on-chip power supply (see Figure 3-1). The power supply provides two different output voltages, V

is the internal power supply voltage except for the driver circuit. Pin VS is used to connect a

block capacitor. V sumption is very low. V

can be switched off by Standby pin. In standby mode, the chip’s power con-

is the supply voltage of the antenna’s pre-driver. This voltage can

EXT

also be used to operate external circuits, like a microcontroller. In conjunction with an external NPN transistor it also establishes the supply voltage of the antenna coil driver, DVS.

and V

EXT

U2270B

4684B–RFID–09/05

3.2 Operation Modes to Power the U2270B

The following section explains the 3 different operation modes to power the U2270B.

3.2.1 One-rail Operation

All internal circuits are operated from one 5-V power rail (see Figure 3-2). In this case, V and DVS serve as inputs. V

Figure 3-2. One Rail Operation Supply

is not used but should also be connected to that supply rail.

Batt

+5 V (stabilized)

U2270B

, V

EXT

3.2.2 Two-rail Operation

In this application, the driver voltage, D 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 ages can be as high as 8 V. This operation mode is intended to be used in situations where an extended communication distance is required.

Figure 3-3. Two Rail Operation Supply

DVSV

EXTVSVBatt

, and the pre-driver supply, V

is connected to a 5-V supply, whereas the driver volt-

EXTVSVBatt

Standby

7 to 8 V (stabilized)

5 V (stabilized)

, are operated at a

EXT

3.2.3 Battery-voltage Operation

Using this operation mode, V

3-4). For this mode, an external voltage regulator is not needed. The IC can be switched off via

the Standby pin. V a microcontroller (even in Standby mode).

Pin V

EXT

and V

4).The maximum current into the pins is determined by the maximum power dissipation and the

maximum junction temperature of the IC.

4684B–RFID–09/05

and V

supplies the base of an external NPN transistor and external circuits, like

EXT

are overvoltage protected via internal Zener diodes (see Figure 3-1 on page

Batt

are generated by the internal power supply (see Figure

EXT

Figure 3-4. Battery Operation

7 to 16 V

DVSV

EXTVSVBatt

Standby

Table 3-1. Characteristics of the Various Operation Modes

Operation Mode External Components Required Supply-voltage Range

One-rail operation

Two-rail operation

1 Voltage regulator 1 Capacitor

2 Voltage regulators 2 Capacitors

5V ±10% ≈ 4V No

5V ±10%

7V to 8V

1 Transistor 2 Capacitors Optional for load

Battery-voltage operation

dump protection:

6V to 16V ≈ 4V Yes

1 Resistor 1 Capacitor

3.3 Oscillator (Osc)

The frequency of the on-chip oscillator is controlled by a current fed into the RF input. An integrated compensation circuit ensures a wide temperature range and a supply-voltageindependent frequency which is selected by a fixed resistor between R For 125 kHz, a resistor value of 110 kΩ is defined. For other frequencies, use the following formula:

14375

Ω[]

--------------------- 5–=

f0kHz

[]

Rtk

Driver Output

Standby Mode

Voltage Swing

6V to 7V No

(pin 15) and VS (pin 14).

Available

This input can be used to adjust the frequency close to the resonance of the antenna. For more details refer to the section “Applications” on page 10” and to the application note ANT019.

Figure 3-5. Equivalent Circuit of Pin R

U2270B

2 kΩ

4684B–RFID–09/05

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