U3280M Datasheet, PDF (3/18 Pages) ATMEL Corporation – TRANSPONDER INTERFACE FOR MICROCONTROLLER

U3280M
Functional Description
Transponder Interface
Modulation
The U3280M is a transponder interface IC that can operate microcontrollers using wire-
less technology 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 detec-
tion 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 possible 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 sup-
ply 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 communication (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 controlled 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.
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 cur-
rent into the coil and damps the coil voltage. A low level (“0”) decreases the current and
increases the coil voltage. The modulator 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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