APPLICATION NOTE LF Driver ATA5279C with Channel Extension Using NMOS Antenna Multiplexer ATA5279C Description Several automotive Passive Entry applications require more than the six LF antennas usually supported by the Atmel® ATA5279C LF driver. Figure 1 on page 2 shows how to expand the device to drive a greater number (9) of LF antennas. In this proposal, an NMOS antenna multiplexer is inserted between output A6P on the ATA5279C driver and the return line A6N. The multiplexer, which is configured by two dual NMOS transistor devices, is controlled directly by a microcontroller and switches the expanded antennas numbers 6 to 9. 9193D-RKE-12/15 Figure 1. Schematic of a Nine-fold Antenna Driver X4_1 D1 R1 L2 + C2 VBATT C1 8V to 16V 2 LD1 Q1 GND TP0 L1 X4_2 D2 TP3 3 1 7 8 44 46 VCC VS OSCO OSCI VL1 VL2 VL3 VDS1 VDS2 X5 X1_12 VCC VDS3 VIF 6 ATA5279C VIF C7 X1_14 PA4 X1_13 PA5 X1_9 PA6 X1_8 PA7 A2P IRQ 41 NRES 40 MACT 9 BCNT A1P 10 A3P IRQ A4P NRES MACT A5P A6P PB4/SS X1_5 PB7/SCK X1_2 PB5/MOSI X1_4 PB6/MISO S_CS 38 39 MOSI 37 MISO 36 A1N2 S_CS A2N2 S_CLK A3N1 MOSI A3N2 MISO A4N1 X1_11 A5N1 A5N2 A6N1 A6N2 CINT CINT VSHF1 VSHF2 VSHS AGND1 AGND3 PGND2 RGND AGND2 PGND1 PGND3 30 A2P 33 A3P 29 A4P 32 A5P 31 35 Ant1 A6P 34 Ce2 Ce3 Ce4 Ce5 Ce6 A7P A8P A1N 24 Ce7 25 A2N 19 Ce8 20 A3N 14 Ce9 15 43 45 Ant9 A4N 22 Ce10 23 A5N 16 Ce11 17 12 13 11 A6N 18 TP2 5 T1 A7N RSH 7/8 28 Antenna Module 47 2 2 X3_1 A1P 1 RINT X6 A9P GND 3 42 26 U1 BCNT A4N2 TP4 27 QFN48 Package A2N1 S_CLK 21 Ce1 A1N1 X1_1 C3 5/6 MCU ATmega 8515 + C4 48 3 4 1 4 C6 TP1 X2_5 R2 R6 X2_9 R3 R7 X1_3 R4 R8 X1_6 R5 R9 A8N 5/6 4 PD6 3 PD2 T2 A9N 2 ATA5279C [APPLICATION NOTE] 9193D–RKE–12/15 2 PB0 7/8 1 PB2 X3_18 Ant8 Ant7 Ant6 Table 1. Bill of Materials for Nine-fold LF Antenna Driver Part No. Designation U1 Transmitter IC Q1 Ceramic Resonator T1 Dual NMOS Value 8MHz Type Manufacturer Atmel ATA5279C Atmel® CSTCE8M00G52A-R0 Murata® BSO615NG Infineon T2 Dual NMOS BSO615NG Infineon D1 Diode Schottky 60V/2A SS26 Vishay® D2 Diode Schottky 60V/2A SS26 Vishay LD1 LED Red TLMT 3100 Vishay R1 Resistor 1.8k SMD 0603 Standard R2 to R5 Resistor 100k SMD 0603 Standard R6 to R9 Resistor 0 SMD 0603 Standard RSH Resistor 1.0/1W/ ±1% tolerance SMD 3520 Standard RINT Resistor 0 SMD 0603 Standard C1 Capacitor Electrolytic 220pF/35V EEUFM1V221 Panasonic® C2 Capacitor Ceramic 100nF SMD 0603 Standard C3 Capacitor Ceramic 10µF/50V GCM32EC71H106K Murata C4 Capacitor Ceramic 100nF SMD 0603 Standard C6 Capacitor Ceramic 100nF SMD 0603 Standard C7 Capacitor Ceramic 100nF SMD 0603 Standard CINT Capacitor Ceramic 10nF SMD 0603 Standard Ce1 to Ce11 Capacitor Ceramic 1nF SMD 0603 Standard EPCOS/ Würth Elektronik EPCOS/ Würth Elektronik L1 Inductor 68µH/2.45A/98m B82477P4683M00 Alternative 744 770 168 L2 Inductor 68µH/2.45A/98m B82477P4683M00 Alternative 744 770 168 ATA5279C [APPLICATION NOTE] 9193D–RKE–12/15 3 1. Considerations when Using the Multiplex Proposal For accurate antenna switching, the NMOS stages need to face the real part of the antenna impedance. Therefore, the antennas’ LC tank must be matched to 125kHz ±5% resonant frequency. With a 3V microcontroller supply, the gate control of the NMOS stages requires a level shifter to 5V or, better, 10V. This is necessary to secure sufficiently high VGS voltage if there is a short-circuit current flowing into the return driver A6N (as this raises the source level of the NMOS). The NMOS transistor stages must be logic-level types, which ensure the low RDSON resistance needed to reach the required breaking current in a short circuit scenario. In addition, the gate capacitance has to be as small as possible to minimize the parasitic leakage current with 125kHz operation. 2. Conclusion This proposal has been tested successfully on the Atmel ATAB5279 application board with the existing GUI software. All functions, including fault scenarios, work properly under laboratory conditions. Nevertheless, the target application needs to be checked for reliable operation over the entire temperature range. 3. Revision History Please note that the following page numbers referred to in this section refer to the specific revision mentioned, not to this document. 4 Revision No. History 9193D-RKE-12/15 Table 1 “Bill of Materials for Nine-fold LF Antenna Driver” on page 3 updated 9193C-RKE-04/15 Put document in the latest template ATA5279C [APPLICATION NOTE] 9193D–RKE–12/15 XXXXXX Atmel Corporation 1600 Technology Drive, San Jose, CA 95110 USA T: (+1)(408) 441.0311 F: (+1)(408) 436.4200 | www.atmel.com © 2015 Atmel Corporation. / Rev.: 9193D–RKE–12/15 Atmel®, Atmel logo and combinations thereof, Enabling Unlimited Possibilities®, and others are registered trademarks or trademarks of Atmel Corporation in U.S. and other countries. Other terms and product names may be trademarks of others. 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