Atmel ATA5283 User Manual
Features
• Wake-up Function for a Microcontroller with Preamble Detection
• 1mV
• 1 µA Standby Current
• Power Supply: 2V to 3.8V
• Baud Rate: up to 4 kbps (ASK Modulation)
• Operation Temperature: up to 125°C
• Withstands +175°C
• Few External Components
Sensitivity
rms
Interface IC for
Application
• Tire Pressure Monitoring (TPM)
1. Description
The ATA5283 is a 125 kHz ultra-low power receiver used for the wake-up function of
Tire Pressure Monitoring (TPM) application. The sensitive input stage of the IC amplifies and demodulates the carrier signal from the antenna coil to a digital output signal
for a microcontroller. During the standby mode the preamble detection unit monitors
the incoming signal and activates the wake-up output and the data output, if the IC
receives a proper 125 kHz carrier signal.
By combining the IC with an antenna coil, a microcontroller, an RF transmitter/transceiver, a battery, temperature- and pressure sensor, it is possible to design a
complete Tire Pressure Monitoring system (TPM).
Figure 1-1. Block Diagram
Battery
Lx
COIL
VDD
Amplifier
with AGC
ATA5283
RESET
125 kHz
Wake-up
Function
ATA5283
TST1
TST2
Vref
Condi-
tioner
GND
Preamble
check
N_WAKEUP
N_DATA
4598H–AUTO–03/07
2. Pin Configuration
Figure 2-1. Pinning TSSOP8L
COIL 8
TST1
TST2
VSS
1
2
3
4
Figure 2-2. Pin Description
Pin Symbol Function
1 COIL Antenna coil input
2 TST1 Test pin (reserved)
3 TST2 Test pin (reserved)
4 VSS Signal ground
5 RESET External reset input
6 N_DATA Data signal
7 N_WAKEUP Low active wake-up signal for microcontroller
8 VDD Battery voltage
VDD
N_WAKEUP
7
N_DATA
6
RESET
5
2
ATA5283
4598H–AUTO–03/07
3. Functional Description
The ATA5283 is an ultra-low power ASK receiver. Without a carrier signal it operates in the
standby listen mode. In this mode it monitors the coil input with a very low current consumption.
To activate the IC and the connected control unit, the transmitting stage must send the preamble
carrier burst. After a preamble is detected the IC is activated. It adapts the gain of the input stage
and enables the wake-up and the data output. The first gap at the end of the preamble generates a wake-up signal for the microcontroller. After that the receiver outputs the data signal at
N_DATA. To return the IC into the standby listen mode it must be reset via the RESET input.
3.1 AGC Amplifier
The input stage contains an Automatic Gain Control (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 enables the IC to operate with input signals from
1mV
an amplitude adjusted for the following evaluation circuits’ preamble detection, signal conditioner, wake-up.
3.2 Preamble Detection
Before data transmission the IC stays in standby listen mode. To prevent the circuit from unintended operations in a noisy environment the preamble detection circuit checks the input signal.
A valid signal is detected by a counter after 192 carrier periods without interrupts. Short interrupts which are suppressed by the signal conditioner are tolerated. When a valid carrier
(preamble) is found the circuit starts the automatic gain control. It requires up to 512 carrier periods to settling. The complete preamble should have 704 carrier periods minimum. The preamble
is terminated and the data transfer is started with the first gap (Start Gap) in the carrier (see Fig-
ure 3-1).
to 1.1V
rms
ATA5283
. After the AGC settling time the amplifier output delivers a 125 kHz signal with
rms
Figure 3-1. Communication Protocol
Procedure
Signal
N_DATA
N_WAKEUP
RESET
Gain
control
Current
profile
192 Periods
of LF
No gain
control
1 µA
Preamble
> 5.64 ms
> 512 Periods
of LF
AGC
adjustment
Start
gap
Gain control
active
Data
0.5 µA2 µA
No gain
control
4598H–AUTO–03/07
3
3.3 Automatic Gain Control
For a correct demodulation the signal conditioner needs appropriate internal signal amplitude.
To control the input signal the ATA5283 has a build in digital AGC. The gain control circuit regulates the internal signal amplitude to the reference value (Ref2, Figure 3-2). It decreases the
gain by one step if the internal signal exceeds the reference level for two periods and it
increases the gain by one step if eight periods do not achieve the reference level. In the standby
listen mode the gain is reset to the maximum value. If a valid preamble signal (192 valid carrier
clocks) is detected the automatic gain control is activated.
Note: With the variation of the gain the coil input impedance changes from high impedance to minimal
143 kΩ because of the internal regulator circuit (see Figure 3-8 on page 8).
Figure 3-2. Automatic Gain Control
Transmitted
signal
input
Coil
Gain control
reference
reference
Gain controlled
signal
Internal comparator
signal
N_DATA
Ref. 2
Ref. 1Gap detection
100%
50%
4
ATA5283
4598H–AUTO–03/07
3.4 Signal Conditioner
The signal conditioner demodulates the amplifier output signal and converts it to a binary signal.
It compares the carrier signal with the 50% reference level (see Ref1 in Figure 3-3) and delivers
a logical 1, if the carrier signal stays below the reference and a logical 0, if it exceeds the reference level. A smoothing filter suppress the space between the half-waves as well as a few
missing periods in the carrier and glitches during the gaps.
The output signal of the signal conditioner is used as the internal data signal for the data output,
the wake-up logic and the preamble detection.
The timing of the demodulated data signal is delayed related to the signal at the transmitting
end. This delay is a function of the carrier frequency, the behavior of the smoothing filter and the
antenna Q-factor. The smoothing filter causes a delay of 3 to 6 periods (see t
3-3). The rest of the delay is caused by the build-up time of the antenna signal and is condi-
tioned on the Q-factor (see t
Figure 3-3. Output Timing
and tc in Figure 3-3).
a
ATA5283
and td in Figure
b
Ref.2
Ref.1
Coil
input
Comparator
output
N_DATA
t
b
t
a
t
ON
t
c
t
d
t
OFF
100%
50%
The following diagrams show the delay of the data signal as a function of the antenna Q-factor.
Figure 3-4. Turn On Delay Time (t
250
f
200
150
(µs)
on
t
100
50
field
) versus Antenna Q-Factor
ON
= 125 kHz
max.
min.
typ.
4598H–AUTO–03/07
0
05040302010
Q-factor
5
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