Designing Next-Generation Car Access Receiver Modules Michael Hahnen and Klaus Herhoffer 15 © 2013 / www.atmel.com Introduction In 1997 Atmel® launched an innovative car access system featuring the lowest current consumption. This was achieved through the self-polling capability of the ATA3741 receiver IC. ATA3741 derivatives and second-generation RF receivers like the ATA572x address new RF automotive application areas. These include tire pressure monitoring system (TPMS), remote start applications, and bi-directional RF links. ATA5743 ATA5723 ATA5724 Sleep 315 MHz Tsleep[ms] 433 MHz Tsleep[ms] Tsleep[ms] Tsleep[ms] 0 cont. On cont. On cont. On cont. On 1 2.12 2.09 2.09 2.12 2 4.24 4.17 4.17 4.24 3 6.36 6.26 6.26 6.36 4 8.48 8.35 8.35 8.48 5 10.60 10.44 10.44 10.60 6 12.72 12.52 12.52 12.72 7 14.84 14.61 14.61 14.83 8 16.95 16.70 16.70 16.95 9 19.07 18.78 18.78 19.07 10 21.19 20.87 20.87 21.19 11 23.31 22.96 22.96 23.31 12 25.43 25.05 25.05 25.43 13 27.55 27.13 27.13 27.55 14 29.67 29.22 29.22 29.67 15 31.79 31.31 31.31 31.79 16 33.91 33.40 33.40 33.91 17 36.03 35.48 35.48 36.03 18 38.15 37.57 37.57 38.15 Both the ATA5743 and the ATA5723/4 are configured by the host controller via one bidirectional line. Both devices have the same internal registers with identical configuration content. You can easily migrate from ATA5743 to ATA5723/24 without any software changes in the host controller. Simply double-check the sleep time settings, since there are some minor timing differences that may require adaptation. Table 1 lists the detailed sleep time changes. 19 40.27 39.66 39.66 40.27 20 42.39 41.74 41.74 42.39 21 44.51 43.83 43.83 44.50 22 46.63 45.92 45.92 46.62 23 48.75 48.01 48.01 48.74 24 50.86 50.09 50.09 50.86 The ATA3741 (formerly named U3741BM) and the ATA5723/4 are likewise configured via one bidirectional line from the host controller. Two internal registers contain the receiver configuration, but the number of bits within the registers differs. To protect the ATA5723/4 against unwanted register content change, the serial communication includes one additional bit. To enable writing content to the addressed register, set bit 15 to low, and add it to the communication software routines in the host controller. 25 52.98 52.18 52.18 52.98 26 55.10 54.27 54.27 55.10 27 57.22 56.35 56.35 57.22 28 59.34 58.44 58.44 59.34 29 61.46 60.53 60.53 61.46 30 63.58 62.62 62.62 63.58 31 cont. Off cont. Off cont. Off cont. Off With leading RF performance and a very reliable RF link, the third generation ATA578x is yet another step ahead. This family includes transceiver and transmitter devices. There are Flash, user ROM, and ROMless versions that are pin, function, and RF-matching compatible. Maximum development re-use minimizes the design efforts for one- and two-way systems. This article describes how to migrate from the earlier ATA3741/43 devices to the current ATA5723/24, or to directly create a new design with Atmel's latest generation ATA578x. Migration to the ATA5723/24 Customers with an RF system based on Atmel's ATA3741/43 UHF receiver ICs can easily upgrade their design to the current generation ATA5723/4. The required modifications to the existing receiver system comprise some very minor software and hardware modifications. Software Modifications Most bits in the registers do have the same meaning and cause the same hardware behavior. Tables 2 and 3 show the two devices' internal registers. Automotive Compilation Vol. 10 Table 1. Sleep Time Settings 16 Bit1 Bit2 Bit2 Bit4 Bit5 Bit6 Bit7 Bit8 Bit9 Bit10 Bit11 Bit12 Bit13 Bit14 OFF Command 1 OPMODE Register 0 1 0 1 NBitcheck BR_Range VPOUT XSleep Sleep Baud1 Baud0 BitChk1 BitChk0 POUT Sleep4 Sleep3 Sleep2 Sleep1 Sleep0 XSleep Std XSleep Temp 0 0 1 0 0 0 1 0 1 1 0 0 (Default) LIMIT Register 0 0 0 0 Lim_min Lim_max Lim_min5 Lim_min4 Lim_min3 Lim_min2 Lim_min1 Lim_min0 Lim_max5 Lim_max4 Lim_max3 Lim_max2 Lim_max1 Lim_max0 (Default) 0 0 1 1 1 0 0 1 1 0 0 0 Table 2. ATA3741 Register Content Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7 Bit 8 Bit 9 Bit 10 Bit 11 Bit 12 Bit 13 Bit 14 Bit 15 – – – – – – XSleep Noise Suppression OFF Command 1 – – – – – – – OPMODE Register – BR_Range 0 – NBit-check 1 Default values of Bit 3...14 Modulation – Sleep Baud1 Baud0 BitChk1 BitChk0 ASK/ _FSK Sleep4 Sleep3 Sleep2 Sleep1 Sleep0 XSleepStd Noise_ Disable 0 0 0 1 0 0 0 1 1 0 0 1 LIMIT Register – 0 Default values of Bit 3...14 – – Lim_min 0 0 Lim_max – Lim_ min5 Lim_ min4 Lim_ min3 Lim_ min2 Lim_ min1 Lim_ min0 Lim_ max5 Lim_ max4 Lim_ max3 Lim_ max2 Lim_ max1 Lim_ max0 0 0 1 0 1 0 1 1 0 1 0 0 1 – Table 3. ATA5723/4 Register Content Bit 7 in the OPMODE register is different. The ATA3741 uses bit 7 to control output pin 17, whereas the ATA5723/4 uses bit 7 to switch between ASK and FSK mode. This switching is done in ATA3741 by pin 2. The upgrade to ATA5723/24 includes a different timing of the programming start pulse. You may also need to do some slight software modifications in the host controller. Please refer to the datasheet section "Programming Start Pulse". With the ATA3741, bit 14 in the OPMODE register extends the sleep time by a factor of 8, whereas the ATA5723/4's bit 14 allows optional additional noise suppression. 17 © 2013 / www.atmel.com Hardware Changes Pin ATA3741 The ATA5723/24 is the direct upgrade of the ATA5743. Both devices are available in SSO20 packages with the same footprint, whereas the ATA3741 package is an SO20. Due to the ATA5723/24's hardware improvements you also need to do some hardware modifications on your board when migrating (table 4). • Faster external oscillator start-up with a negative resistor up to 1.5kΩ (only valid for migration from ATA5743 to ATA5723/24) • The ATA5723/4 requires a crystal with a different frequency • Less external components on the ATA5723/24 board due to integration of the filter circuit ATA5743 ATA5723/4 2 FSK/ASK 6 GND GND Open (RSSI) 7 VS VS GND 8 GND (with filter) GND (with filter) GND 9 Antenna matching Antenna matching Antenna matching 10 NC NC GND 11 VS VS NC 12 Filter circuit Filter circuit GND 13 GND GND XTAL2 14 XTAL XTAL XTAL1 17 POUT Data clock 19 Enable High = polling on Low = sleep Polling High = polling on, Low = receiving active • The antenna matching elements have to be modified IC_Active Table 4. List of Hardware Differences VCC GND X3 + C7 2.2µF JP1 C6 10nF X7R X4 R2 56kΩ 2% C13 33nF X7R C14 33nF X7R 5% C3 15pF np0 5% C17 3.3pF np0 5% 1 2 3 5 6 7 8 9 10 ENABLE FSK/ASK CDEM TEST AVCC POUT AGND MODE DGND DVCC MIXVCC XTO LNAGND LFGND LF LNA_IN LFVCC n.c. Printed Inductor > 25nH C16 100pF np0 ± 0.1pF L2 22nF 5% ENABLE DATA SENS C12 10nF X7R VS = +5V GND DATA MODE U1 U3741BM 4 C15 150pF np0 5% X1 SMB 12 R3 27kΩ 1 20 JP2 19 18 17 16 R5 10kΩ R4 0 15 14 13 Q1 6.76438MHz HC49/U3H 12 11 C8 4.7nF X7R 5% C9 4.7nF X7R 5% R1 820Ω 5% C11 12pF np0 5% R6 n.m. C10 1nF X7R 5% all Inductors: Toko LL2012FH Figure 1. Typical Application ATA3741 Automotive Compilation Vol. 10 18 VS + C7 2.2µF 20% C6 10nF 10% X7R C14 5% 33nF C13 10nF X7R 10% C3 15pF ATA5743 1 2 3 SENS DATA IC_ACTIVE POLLING /_ON 4 5 6 7 AVCC TEST AGND CDEM 5% np0 DGND DATA_CLK MODE DVCC XTO MIXVCC 8 9 10 LFGND LF LFVCC LNAGND LNA_IN NC 150pF C15 C17 DATA_CLK 16 6.7643 MHz 15 14 13 12 11 33nH 5% C11 12pF 5% np0 Q1 C8 150pF np0 10% C16 L2 DATA POLLING/_ON 10 nF 10% X7R np0 10% 1.5pF 5% np0 R3 >1.6kΩ 20 19 18 17 C12 25 nH Sensitivity Reduction VX = 5V to 20V 56kΩ to 150kΩ 10% GND COAX IC_ACTIVE R2 R1 100pF 5% np0 820Ω 5% C9 C10 4.7nF 1nF X7R 5% X7R 5% Figure 2. Typical Application with ATA5743 VS RSSI + C7 4.7µF 10% IC_ACTIVE R2 Sensitivity Reduction 56kΩ to 150kΩ VX = 5V to 20V GND C14 39nF 5% 1 2 3 4 C13 10nF 10% 6 7 8 C17 RF_IN 5 9 C16 10 L1 DATA SENS IC_ACTIVE POLLING/_ON DGND CDEM DATA_CLK AVCC TEST1 RSSI AGND ATA5723 ATA5724 ATA5728 MODE DVCC XTAL2 LNAREF XTAL1 LNA_IN TEST3 LNAGND TEST2 R3 1.6kΩ 20 DATA 19 POLLING/_ON 18 17 16 15 DATA_CLK C12 10nF 10% 14 13 12 11 CL2 F Crystal CL1 Figure 3. Typical Application with ATA5723/24 19 © 2013 / www.atmel.com IRQ NSS VS 8 PB3 PB4 PB5 PB6 PB7 PB0 Atmel ATA5781 ATA5782 ATA5783 SPDT_ANT NC DGND DVCC 24 23 22 20 19 NC PC4 18 VS_SPDT PC3 17 TEST _EN 9 10 11 12 13 14 15 SCK CLK_IN 21 PC5 SPDT_RX2 MOSI Microcontroller PC2 7 MISO 25 SPDT_RX PC1 6 26 PB1 PC0 5 27 RFIN_HB VS 4 SAW 28 PB2 AVCC 3 29 XTAL2 2 30 ATEST ATEST _IO1 _IO2 RFIN_LB XTAL1 1 31 AGND 32 16 VS = 5V VDD Figure 4. Typical Application Circuit with 5V Power Supply Automotive UHF Receiver Design Based on ATA5781/2/3 All members of Atmel's ATA5781/2/3 family include an AVR® microcontroller core. Designed for the ISM frequency bands (310-318MHz, 418-477MHz and 836-956MHz), these parts feature excellent RF receiving sensitivity. In FSK mode, the sensitivity reaches –122.5dBm (at 433.92MHz, 0.75kbit/s and BWIF = 25kHz), in ASK mode sensitivity is –125dBm (at 433.92MHz, 0.5kbit/s and BWIF = 25kHz). The autonomous self-polling mode and good blocking performance help you to design robust automotive RF receiver systems with very low power consumption, since only a valid RF signal activates the host controller. Excellent RF performance, a short bill of materials, and flexibility to adapt the receiving behaviour to all known RF protocols and market needs make the ATA578x family the best choice for new RF receiver designs. Configuration The AVR microcontroller's ROM includes firmware that allows you to configure the device according to the configuration stored in the EEPROM. You can control the receiver via an external host controller by using the SPI interface. User Flash and user ROM (available in ATA5782 and ATA5783 only) enable you to write additional software. For example, to protect the external host controller, or to adapt the firmware to any RF protocol. The receiver families have different program memory capabilities (see table 5). Part Number ROM Firmwave ATA5781 24KByte ATA5782 24KByte ATA5783 24KByte User Flash User ROM 5V Power Supply Application In automotive remote keyless entry (RKE) systems, you use the ATA578x as an UHF receiver inside the vehicle. Such applications typically connect to a regulated 5V power supply (see figure 4). The host MCU controls the RF receiver via the SPI interface. The receiver operates autonomously. The host controller just enables the receiving mode, either polling RX mode or standard RX mode, by sending the corresponding command over the SPI lines. RF Settings In modern vehicles an RF receiver must be capable of receiving different RF protocols from different transmitters. This includes RKE key fobs, tire pressure monitoring systems, and remote start controls. Because these systems transmit their messages with different modulation, baud rate, and bandwidth, the ATA578x family offers five different RF settings to let you define the RF protocol and the wake-up conditions via the EEPROM configuration GUI (graphical user interface). Reception Modes You can use two different reception modes. During standard Rx mode the receiver checks for a desired RF telegram at a particular time. Polling mode means that you define the telegram settings in advance. The receiver automatically and continuously checks for this defined setting. Once the receiver detects the beginning of a valid signal it switches to standard Rx mode and receives the message. In case of no valid message, the receiver switches off for a defined period, and the entire procedure starts over again. 20KByte 20KByte Table 5. Program Memory Automotive Compilation Vol. 10 20