Rev. 4694BAUTO06/04
Features
Three Input Channels for 3D Antennas
2.8 mV
PP
Sensitivity Typically
Ultra Low Current Operation Consumption
2 A Standby Current Typically
4 A Active Current Typically
Power Supply 2 V to 4.2 V
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 2.8 V
PP
Typically
High Sensitivity
Applications
Passive Entry Go (PEG)/Car Access
Position Indicator
Home Access Control
RFID Systems
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.
Ultra Low Power
125 kHz 3D -
Wake-up
Receiver with
RSSI
ATA5282
Preliminary
2
ATA5282 [Preliminary]
4694BAUTO06/04
Figure 1. Block Diagram
Pin Configuration
Figure 2. Pinning TSSOP 8L
ATA5282
3 Channel Amplifier
with AGC
NDATA/
NWAKEUP
Signal
conditioner
Header
detection
VDD
VSS
Vref
Battery
TC
Serial
interface
select
field strength
NSCL
3
8
Timing
control
L2
L1
L3
Pin Description
Pin
Symbol
Function
1
COIL1
Input: Coil channel X
2
COIL2
Input: Coil channel Y
3
COIL3
Input: Coil channel Z
4
VSS
Circuit ground
5
TC
Output: Current output for oscillator adjustment
6
NSCL
Input: Clock for serial interface (default high)
7
NDATA
Input/Output: I/O data for serial interface and field strength measurement/
Wake-up function (default high)
8
VDD
Battery voltage
COIL1
COIL2
COIL3
VSS
VDD
NDATA
NSCL
TC
1
2
3
4
8
7
6
5
3
ATA5282 [Preliminary]
4694BAUTO06/04
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
monitors 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 3.1 V
PP
it is neces-
sary to control the gain of the amplifiers. Each of the 3 input stages contain an amplifier
with Automatic 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.
4
ATA5282 [Preliminary]
4694BAUTO06/04
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. ATA5282 State Diagram
Stand by
Waiting for
RF-signal
Preamble
check
Signal detected
Count
192 periods
Gap detected
after 192 periods
Gap detected
before
192 periods
Check 8 edges of
demodulated signal
No valid header
within 2 ms
Wake up
micro-
controller
360 ms
watchdog
20 ms
quietness
check
Header
timeout
Stop if
header ok
Header ok
Oscillator
run
Start header
check
Start header
timeout
check
Start quietness
check
Start watchdog
Switch
demodulated
signal to data
output
Enable
data output
Restart if
signal
detected
No data received
for 20 ms
360 ms
gone
Header
timing
check
5
ATA5282 [Preliminary]
4694BAUTO06/04
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 3.1 V
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).
Automatic Gain Control
For correct demodulation, the signal conditioner needs an appropriate internal signal
amplitude. 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 ref-
erence level (Ref2, Figure 4 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 deforma-
tion 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. To accelerate the settling time, fast gain control mode can be activated via the
serial interface. In this mode, the tuning range is subdivided into 128 steps and the set-
tling time is two times faster.
In standby listen mode, the gain is reset to the maximum value. A proper carrier signal
activates the automatic gain control.
The preamble (Figure 9 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 s (32 periods of 125 kHz).
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