Features
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Contactless Power Supply and Communication Interface
Up to 10 kbaud Data Rate (R/O)
Power Management for Contactless and Battery Power Supply
Frequency Range 100 kHz to 150 kHz
32 x 16-bit EEPROM
Two-wire Serial Interface
Shift Register Supported Bi-phase and Manchester Modulator Stage
Reset I/O Line
Field Clock Extractor
Field and Gap Detection Output for Wake-up and Data Reception
Field Modulator with Energy-saving Damping Stage
Applications
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Main Areas
– Access Control
– Telemetry
– Wireless Sensors
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Examples:
– Wireless Passive Access and Active Alarm Control for Protection of Valuables
– Contactless Position Sensors for Alignments of Machines
– Contactless Status Verification and/or Data Readout from Sensors
Transponder
Interface for
Microcontroller
U3280M
1. Description
The U3280M is a transponder interface for use in contactless ID systems, remote con-
trol systems, tag and sensor applications. It supplies the microcontroller with power
from an RF field via an LC-resonant circuit and it enables contactless bi-directional
data communication via this RF field. It includes power management that handles
switching between the magnetic field and a battery power supply. To store permanent
data like an identifier code and configuration data, the U3280M includes a 512-bit
EEPROM with a serial interface.
4688D–RFID–03/07
3. Functional Description
3.1
Transponder Interface
The U3280M is a transponder interface IC that can operate microcontrollers using wireless tech-
nology and battery independently. Wireless data communication and the power supply are
handled via an electromagnetic field and the coil antenna of the transponder interface. The
U3280M consists of a rectifier stage for the antenna, power management to handle field and
battery power supplies, a damping modulator, and a field-gap detection stage for contactless
data communication. Furthermore, a field clock extraction and an EEPROM are on-chip.
The internal rectifier stage rectifies the AC from the LC-resonant circuit at the coil inputs and
supplies the U3280M device and an additional microcontroller device with power. It is also possi-
ble to supply the device via the V
Batt
input with DC from a battery. The power management
handles switching between battery supply (V
Batt
pin) and field supply automatically. It switches to
field supply if a field is applied at the coil, and it switches back to battery if the field is removed.
The voltage from the coil or the V
Batt
pin is output at the V
DD
pin to supply the microcontroller or
any other suited device. At the V
DD
pin a capacitor must be connected to smooth and buffer the
supply voltage. This capacitor is also necessary to buffer the supply voltage during communica-
tion (damping and gaps in the field).
For communication, the chip contains a damping stage and gap-detect circuitry. By means of the
damping stage the coil voltage can be modulated to transmit data via the field. It can be con-
trolled with the modulator input (MOD pin) via the microcontroller. The gap-detection circuitry
detects gaps in the field and outputs the gap/field signal at the gap-detect output (Pin NGAP).
To store data like keycodes, identifiers and configuration bits, a 512-bit EEPROM is available
on-chip. It can be read and written by the microcontroller via a two-wire serial interface.
The serial interface, the EEPROM and the microcontroller are supplied with the voltage at the
V
DD
pin. That means the microcontroller can read and write the EEPROM if the supply voltage at
V
DD
is in the operating range of the IC.
The U3280M has built-in operating modes to support a wide range of applications. These modes
can be activated via the serial interface with special mode control bytes.
To support applications with battery supply only, power management can be switched off by
software to disable the automatic switching to field supply.
An on-chip Bi-phase and Manchester modulator can be activated and controlled by the serial
interface. If this modulator is used, it modulates the serial data stream at the serial inputs SDA
and SCL into a Bi-phase or Manchester-coded signal for the damping stage.
3.2
Modulation
The transponder interface can modulate the magnetic field by its damping stage to transmit data
to a base station. It modulates the coil voltage by varying the coil’s load. The modulator can be
controlled via the MOD pin. A high level (“1”) increases the current into the coil and damps the
coil voltage. A low level (“0”) decreases the current and increases the coil voltage. The modula-
tor generates a voltage stroke of about 2 V
pp
at the coil. A high level at the MOD pin makes the
maximum of the field energy available at V
DD
. During reset mode, a high level at the MOD pin
causes optimum conditions for starting the device and charging the capacitor at V
DD
after the
field has been applied at the coil.
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U3280M
4688D–RFID–03/07
U3280M
3.2.1
Digital Input to Control the Damping Stage (MOD)
MOD = 0: coil not damped
V
coil-peak
= V
DD
×
2 + V
CMS
= V
CU
MOD = 1: coil damped
V
coil-peak
= V
DD
×
2 = V
CD
V
CMS
= V
CID
: modulation voltage stroke at coil inputs
Note:
If the automatic power management is disabled, the internal front-end V
DD
is limited at V
DDC
. In
this case the value V
DDC
must be used in the above formula.
3.3
Field Clock
The field clock extractor of the interface makes the field clock available for the microcontroller. It
can be used to supply timer inputs to synchronize modulation and demodulation with the field
clock.
3.4
Gap Detect
The transponder interface can also receive data. The base station modulates the data with short
gaps in the field. The gap-detection circuit detects these gaps in the magnetic field and outputs
the NGAP/field signal at the NGAP pin. A high level indicates that a field is applied at the coil
and a low level indicates a gap or that the field is off. The microcontroller must demodulate the
incoming data stream at one of its inputs.
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4688D–RFID–03/07
Power technology
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