Features
•
•
•
•
•
•
•
•
•
•
•
•
Three Input Channels for 3D Antennas
2.8 mV
PP
Sensitivity Typically
Ultra Low Current Operation Consumption
2 µA Standby Current Typically
4 µA Active Current Typically
Power Supply 2V to 3.8V
Carrier Frequency Range from 100 kHz to 150 kHz
Wake-up Function for a Microcontroller
Header Detection
Baud Rate up to 4 kbps (ASK Modulation)
Bi-directional Two-wire Interface
ESD According to Automotive Requirements
Benefits
•
Digital RSSI for Field Strength Measurement
•
Coils Input Range from 2.8 mV
PP
to 2.8V
PP
Typically
•
High Sensitivity
Ultra Low Power
125 kHz 3D -
Wake-up
Receiver with
RSSI
ATA5282
Applications
•
•
•
•
Passive Entry Go (PEG)/Car Access
Position Indicator
Home Access Control
RFID Systems
1. Description
The ATA5282 is a 125-kHz ultra low power receiver IC with three input channels for
Passive Entry Go applications. It includes all circuits for an LF wake-up channel. The
three sensitive input stages of the IC amplifier demodulate and measure the input sig-
nal from the antenna coils. The microcontroller interface of the IC outputs the data
signal as well as the measured RSSI values. During standby mode, the header detec-
tion unit monitors the incoming signal and generates a wake-up signal for the
microcontroller if the IC receives a valid 125-kHz carrier signal.
By combining the IC with an antenna coil, a microcontroller, an RF transmitter/trans-
ceiver and a battery, it is possible to design a complete hands-free key for Passive
Entry Go applications.
4694E–AUTO–08/05
Figure 1-1.
Block Diagram
Battery
VDD
TC
VSS
ATA5282
3 Channel Amplifier
with AGC
L1
Timing
control
L2
Signal
conditioner
Header
detection
NDATA/
NWAKEUP
L3
select
3
Vref
8
field strength
Serial
interface
NSCL
2. Pin Configuration
Figure 2-1.
Pinning TSSOP 8L
COIL1
COIL2
COIL3
VSS
1
2
3
4
8
7
6
5
VDD
NDATA
NSCL
TC
Table 2-1.
Pin
1
2
3
4
5
6
7
8
Pin Description
Symbol
COIL1
COIL2
COIL3
VSS
TC
NSCL
NDATA
VDD
Function
Input: Coil channel X
Input: Coil channel Y
Input: Coil channel Z
Circuit ground
Output: Current output for oscillator adjustment
Input: Clock for serial interface (default high)
Input/Output: I/O data for serial interface and field strength measurement/
Wake-up function (default high)
Battery voltage
2
ATA5282
4694E–AUTO–08/05
ATA5282
3. Functional Description
The ATA5282 is a 3-channel ASK receiver for 125-kHz carrier signals. Its three active input
stages with very low power consumption and high input sensitivity allow to connect up to 3
antennas for direction-independent wake-up function and data transfer.
Without a carrier signal the ATA5282 operates in standby listen mode. In this mode, it moni-
tors the 3 Coil inputs with a very low current consumption. To activate the IC and the
connected control unit, the transmitting end must send a preamble carrier burst and the
header code. When a preamble has been detected, the IC activates the internal oscillator and
the header check. The last gap at the end of a valid header enables the NDATA output.
During data transfer, the NDATA pin outputs the demodulated and merged signal of the 3
input stages.
To achieve data rates up to 4 kbps for input signals from 2.8 mV
PP
to 2.8V
PP
it is necessary to
control the gain of the amplifiers. Each of the 3 input stages contain an amplifier with Auto-
matic Gain Control (AGC). It is used to adapt the gain to the incoming signal strength, and is
also used as RSSI for field strength measurements.
The integrated synchronous serial interface uses the NSCL together with the NDATA pin as
clock and data line. It allows to control several functions as well as read out the received signal
field strength. Enabling only single coil inputs, freezing the actual status of the automatic gain
control or resetting the complete circuit to the initial state at any time are built-in features.
When communication is finished or a time out event occurs, the internal watchdog timer or
reset command via the serial interface sets the IC to standby listen mode.
3
4694E–AUTO–08/05
3.1
Functional State Diagram
This diagram gives an overview of the major tasks performed by the ATA5282. The detailed
function of the automatic gain control that is active during preamble check, header check and
data transfer is not shown here.
Figure 3-1.
ATA5282 State Diagram
Stand by
Waiting for
RF-signal
Signal detected
Gap detected
before
192 periods
Count
192 periods
Preamble
check
No valid header
within 2 ms
Gap detected
after 192 periods
360 ms
gone
No data received
for 20 ms
Oscillator
run
Start watchdog
Start header
check
Start header
timeout
check
Check 8 edges of
demodulated signal
Header
timing
check
Header
timeout
Header ok
Stop if
header ok
Wake up
micro-
controller
Start quietness
check
360 ms
watchdog
Enable
data output
20 ms
quietness
check
Restart if
signal
detected
Switch
demodulated
signal to data
output
4
ATA5282
4694E–AUTO–08/05
ATA5282
3.2
AGC Amplifier
Each of the three input stages contain an AGC amplifier to amplify the input signal from the
Coil. The gain is adjusted by the automatic gain control circuit if a preamble signal is detected.
The high dynamic range of the AGC amplifier enables the IC to work with input signals from
2.8 mV
PP
to 2.8V
PP
. After the AGC settling time has elapsed, the amplifier output delivers a
125-kHz signal with an amplitude adjusted for the following evaluation circuits (preamble
detection, signal conditioner, wake-up).
3.3
Automatic Gain Control
For correct demodulation, the signal conditioner needs an appropriate internal signal ampli-
tude. To control the input signal, the ATA5282 has a built-in digital AGC for each input
channel. This gain control circuit regulates the internal signal amplitude to the reference level
(Ref2,
Figure 3-2 on page 6).
The gain control uses the signal of the input channel with the
highest amplitude for the regulation as well as signal for the signal conditioner.
During the preamble, each period of the carrier signal decreases the gain if the internal signal
exceeds the reference level. If the signal does not achieve the reference level, each period
increases the gain. After 192 preamble periods, the standard gain control mode is activated. In
this mode, the gain is decreased every two periods if the internal signal exceeds the reference
level and increased every eight periods if the reference level is not achieved. These measures
assure that the input signal’s envelope deformation will be minimized.
During the gaps between signal bursts, the gain control is frozen to avoid that the gain be
modified by noise signals.
The tuning range of the AGC is subdivided into 256 regulator steps. The settling time for the
full tuning range requires 320 periods (192 + (2
×
64) periods) during a preamble phase.
In standby listen mode, the gain is reset to the maximum value. A proper carrier signal acti-
vates the automatic gain control.
The preamble (Figure
3-7 on page 10)
with up to 320 periods of the 125 kHz magnetic field is
used to control the gain of the input amplifiers. To detect the starting point of the header, the
start gap should not exceed 256 µs (32 periods of 125 kHz).
5
4694E–AUTO–08/05
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