Features
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
Main Areas
Access Control
Telemetry
Wireless Sensors
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
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.
Figure 1. Block Diagram
Damping
stage
512-bit
EEPROM
memory
Coil 1
Coil 2
VSS
Low power
microcontroller
Rectifier
VDD
Field/gap
detect
VBatt
MOD
NGAP
Bi-phase
modulator
Serial
interface
Clock
extractor
FC
Power
management
>
_1
VField
regulator
SCL
SDA
Transmit data
Field clock
Data
Energy
NRST
Sensors, keys, displays, actuators
Receive data/field detected
U3280M Transponder Interface
Transponder
Interface for
Microcontroller
U3280M
Rev. 4688BRFID12/04
2
U3280M
4688BRFID12/04
Pin Configuration
Figure 2. Pinning
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VBatt
VDD
SCL
NRST
SDA
VSS
NC
FC
Coil 2
Coil 1
NC
NC
NC
NC
NGAP
MOD
Pin Description
Pin
Symbol
Function
1
VBatt
Power supply voltage input to connect a battery
2
VDD
Power supply voltage for the microcontroller and EEPROM. At this pin a buffer capacitor (0.5 to 10 F)
must be connected to buffer the voltage during field supply and to block the VDD of the microcontroller.
3
SCL
Serial clock line
4
NRST
Reset line bi-directional
5
SDA
Serial data line
6
VSS
Circuit ground
7
NC
Not connected
8
FC
Field clock output of the front-end clock extractor
9
MOD
Modulation input
10
NGAP
Gap and field detect output
11
NC
Not connected
12
NC
Not connected
13
NC
Not connected
14
NC
Not connected
15
Coil 1
Coil input 1. Use pin to connect a resonant circuitry for communication and field supply
16
Coil 2
Coil input 2. Use pin to connect a resonant circuitry for communication and field supply
3
U3280M
4688BRFID12/04
Functional Description
Transponder Interface
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.
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 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.
4
U3280M
4688BRFID12/04
Digital Input to Control the
Damping Stage (MOD)
MOD = 0: coil not damped
MOD = 1: coil damped
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.
Field Clock
The field clock extractor of the interface makes the field clock available for the microcon-
troller. It can be used to supply timer inputs to synchronize modulation and
demodulation with the field clock.
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.
U3280M Signals and Timing
Figure 3. Modulation
Figure 4. GAP and Modulation Timing
V
coil-peak
V
DD
2
V
CMS
V
CU
=
+
=
V
coil-peak
V
DD
2
V
CD
=
=
MOD
Coil inputs
V
CMS
V
CU
V
CD
t
FBS
t
BFS
Coil supply if automatically power management is enabled
Battery
supply
Battery supply
Coil inputs
NGAP
Field clock FC
Power
management
1. edge used as wakeup signal
t
FGAP0
V
FDON
t
FGAP1
V
FDOFF
Gap detection and battery to field switching
5
U3280M
4688BRFID12/04
Digital Output of the
Gap-detection Stage
(NGAP)
NGAP = 0: gap detected/no field
V
coil-peak
= V
FDoff
NGAP = 1: field detected
V
coil-peak
= V
FDon
Note:
No amplifier is used in the gap-detection stage. A digital Schmitt trigger evaluates the
rectified and smoothed coil voltage.
Wake-up Signal
If a field is applied at the coil of the transponder interface, the microcontroller can be
woken up with the wake-up signal at the NGAP pin. For that purpose, the NGAP pin
must be connected to an interrupt input of the microcontroller. A high level at the NGAP
output indicates an applied field and can be used as a wake-up signal for the microcon-
troller via an interrupt. The wake-up signal is generated if power management switches
to field supply. The field-detection stage of the power management has lowpass charac-
teristics to avoid generating wake-up signals and unnecessary switching between
battery and field supply in case of interferences at the coil inputs.
Power Supply
The U3280M has a power management that handles two power supply sources. Nor-
mally, the IC is supplied by a battery at the V
Batt
pin. If a magnetic field is applied at the
LC-resonant circuit of the device, the field detection circuit switches automatically from
V
Batt
to field supply.
The V
DD
pin is used to connect a capacitor to smooth the voltage from the rectifier and
to buffer the power while the field is modulated by gaps and damping. The EEPROM
and the connected controller always operate with the voltage at the V
DD
pin.
Note:
During field supply the maximum energy from the field is used if a high level is applied at
the MOD input.
Automatic Power
Management
There are different conditions that cause a switch from the battery to field and back from
field to the battery.
The power management switches from battery to field if the rectified voltage (V
coil
) from
the coil inputs becomes higher than the field-on-detection voltage (V
FDon
), even if no bat-
tery voltage is available (0 < V
Batt
< 1.8 V). It switches back to battery if the coil voltage
becomes lower than the field-off-detection voltage (V
FDoff
).
The field detection stage of the power management has low pass characteristics to sup-
press noise. An applied field needs a time delay t
BFS
(battery-to-field switch delay) to
change the power supply. If the field is removed from the coil, the power management
will generate a reset that can be connected to the microcontroller.
Figure 5. Switch Conditions for Power Management
Note:
The rectified supply voltage from the coil is limited to V
DDC
(2.9 V). During field supply,
the battery is switched off and V
DD
changes to V
DDC
.
Battery
supply
Field
supply
V
Coil
> V
FDon
for t > t
BFS
V
Coil
< V
FDon
for t > t
BFS
(V
Batt
)
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