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Fabricante : Atmel
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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 Conditioner Amplifier with AGC Preamble check N_WAKEUP N_DATA RESET COIL Vref GND VDD ATA5283 Battery Lx TST1 TST2 Interface IC for 125 kHz Wake-up Function ATA5283 4598H–AUTO–03/07 3 4 2 1 2. Pin Configuration Figure 2-1. Pinning TSSOP8L COIL TST1 TST2 VSS Figure 2-2. Pin Description 8 VDD 7 N_WAKEUP 6 N_DATA 5 RESET 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 ATA5283 4598H–AUTO–03/07 ATA5283 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 to 1.1V. After the AGC settling time the amplifier output delivers a 125 kHz signal with rmsrms 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 Figure 3-1). Figure 3-1. Communication Protocol Preamble Start Procedure Data > 5.64 ms gap 192 Periods > 512 Periods of LF of LF Signal N_DATA N_WAKEUP RESET Gain No gain AGC Gain control No gain control adjustment active control control Current 2 .A 0.5 .A 1 .A profile 4598H–AUTO–03/07 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 k. because of the internal regulator circuit (see Figure 3-8 on page 8). Figure 3-2. Automatic Gain Control Transmitted signal Internal comparator signal Gain controlled signal Coil input Ref. 1 Gap detection reference Ref. 2 100% 50% Gain control reference N_DATA ATA5283 4598H–AUTO–03/07 ATA5283 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 peri...