AND9148/D NCV7383 FlexRay) Bus Driver Application Note http://onsemi.com INTRODUCTION NCV7383 is a single-channel FlexRay bus driver compliant with the FlexRay Electrical Physical Layer Specification Rev. 3.0.1, capable of communicating at speeds of up to 10 Mbit/s. It provides differential transmit and receive capability between a wired FlexRay communication medium on one side and a protocol controller and a host on the other side. NCV7383 mode control functionality is optimized for nodes without the need of extended power management provided by transceivers with permanent connection to the car battery as is on NCV7381. NCV7383 is primarily intended for nodes switched off by ignition. PIN CONNECTIONS VIO TxD TxEN RxD BGE STBN SCLK This document provides additional information on following topics: Typical Application Optional ESD protection Example PCB layout Digital outputs DC characteristics Communication Controller interface termination Bus impedance in Power-off mode ECU IN OUT CVIO VIO (Top View) VBAT IN OUT CVCC VCC TxD Rtxd TxEN Rtxen Rrxd Bus Guardian Host Interface SPI RxD BGE STBN ERRN CSN SCK SDO NCV7383 CMC BP BP BM BM GND CBUS RBUS2 FlexRay Communication Controller VCC BP BM GND ERRN CSN SDO VCC reg. VIO reg. MCU 1 RBUS1 • • • • • • APPLICATION NOTE ESD GND Figure 1. NCV7383 Application Diagram © Semiconductor Components Industries, LLC, 2013 June, 2013 − Rev. 0 1 Publication Order Number: AND9148/D AND9148/D TYPICAL APPLICATION Table 1. NCV7383: RECOMMENDED EXTERNAL COMPONENTS Component Function Value Unit Note CVCC Decoupling capacitor on VCC supply line, ceramic (X7R) 100 nF Type 0603 CVIO Decoupling capacitor on VIO supply line, ceramic (X7R) 100 nF Type 0603 RBUS1 Bus termination resistor 47.5 W Type 0805, (Note 1) RBUS2 Bus termination resistor 47.5 W Type 0805, (Note 1) CBUS Common-mode stabilizing capacitor, ceramic 4.7 nF Type 0805, ±20% CMC Common-mode chokes 100 mH (Note 2) ESD Optional ESD protection NUP2115 - Type SOT-23 Rtxd Optional TxD line series termination resistor (Note 3) Type 0603 Rtxen Optional TxEN line series termination resistor (Note 3) Type 0603 Rrxd Optional RxD line series termination resistor (Note 3) Type 0603 1. Tolerance ±1%; the value RBUS1+RBUS2 should match the nominal cable impedance. 2. Recommended common-mode chokes: MURATA DLW43SH101XK2 MURATA DLW43SH510XK2 MURATA DLW43SH101XP2 EPCOS B82799C0104N001 TDK ACT45R-101-2P-TL001 3. See Communication Controller Interface Termination section. Optional ESD Protection Table 2. SYSTEM HBM ON PINS BP AND BM, per IEC 61000-4-2; 150 pF/330 W In order to improve system reliability an additional external ESD protection may be used. As a result of the high speed nature, the FlexRay specification calls for a low capacitance protection of up to 20 pF and a tight deviation in capacitance between the signal pairs limited to 2%. The reason is that any additional ESD protection represents a capacitive load on the bus lines which can have undesired effects on electromagnetic emissions and immunity if the bus lines capacitive load does not match properly. The NUP2115, dual line FlexRay Bus Protector, is designed for the highest possible signal integrity by limiting the stray capacitance to 10 pF max while having a nominal capacitance matching at 0.26% and achieving the ESD and other transient protection requirements. NCV7383 Requirement NCV7383 + NUP2115L ±6 kV Pin No failure up to: BP ±13 kV ±21 kV BM ±13 kV ±21 kV For more information on the device details, see the product datasheet [4]. Example PCB Layout An example PCB layout is shown in the Figure 3. Modification of this layout is possible with the following recommendations: • Place the NCV7383, the common mode choke and the optional ESD protection as near as possible to the BP and BM pins of the ECU connector. • Route the BP and BM signal lines symmetrically. • Keep the distance between the lines BP and BM minimal. • Keep the decoupling capacitors close to the particular supply pins. • Keep the ground plane uninterrupted if possible. Figure 2. SOT−23 Package System ESD measurement results are shown in the Table 2. Tested without external bus filter network, which is the worst case. The absolute values are from internal measurements. It indicates noticeable increase of the maximum possible discharge voltage. The values measured by external laboratory are visible in device datasheets [1][4]. http://onsemi.com 2 AND9148/D Top Layer Copper Bottom Layer Copper Through hole via Figure 3. Example PCB Layout Digital Outputs DC Characteristics Typical digital outputs (RxD, ERRN and SDO) characteristics are shown in the Figure 6 to Figure 11. The characteristics were measured at room ambient temperature, in Normal mode (STBN and EN forced High), with no undervoltage and with supply voltages: VBAT = 12 V, VCC = 5 V, VIO = 3.3 V and 5 V. VIO LOW VIO DOUT V DOUT HIGH iDOUT V (VIO−uDOUT) uDOUT −iDOUT GND GND Figure 4. Test Setup for Output Low Characteristics on Digital Output Pins Figure 5. Test Setup for Output High Characteristics on Digital Output Pins RxD Digital Output 1200 1200 TEMP = 25°C TEMP = 25°C 1000 VIO−uRxDOH, VIO−OUTPUT VOLTAGE (mV) uRxDOL, OUTPUT VOLTAGE (mV) 1000 800 600 400 VIO = 3.3 V 200 0 VIO = 5 V 0 5 10 15 20 25 800 600 400 VIO = 3.3 V 200 0 30 VIO = 5 V 0 5 10 15 20 25 30 iRxDOL, OUTPUT SINK CURRENT (mA) −iRxDOH, OUTPUT SOURCE CURRENT (mA) Figure 6. Typical RxD Output Sink Characteristics Figure 7. Typical RxD Output Source Characteristics http://onsemi.com 3 AND9148/D ERRN Digital Output 1200 1200 TEMP = 25°C 1000 1000 VIO−uERRNOH, VIO−OUTPUT VOLTAGE (mV) uERRNOL, OUTPUT VOLTAGE (mV) TEMP = 25°C 800 600 400 VIO = 3.3 V 200 0 VIO = 5 V 0 1 2 3 4 800 600 400 VIO = 3.3 V 200 0 5 VIO = 5 V 0 1 2 3 4 5 iERRNOL, OUTPUT SINK CURRENT (mA) −iERRNOH, OUTPUT SOURCE CURRENT (mA) Figure 8. Typical ERRN Output Sink Characteristics Figure 9. Typical ERRN Output Source Characteristics SDO Digital Output 1200 1200 TEMP = 25°C 1000 1000 VIO−uSDOOH, VIO−OUTPUT VOLTAGE (mV) uSDOOL, OUTPUT VOLTAGE (mV) TEMP = 25°C 800 600 400 VIO = 3.3 V 200 0 VIO = 5 V 0 1 2 3 4 800 600 400 VIO = 3.3 V 200 0 5 VIO = 5 V 0 1 2 3 4 iSDOOL, OUTPUT SINK CURRENT (mA) −iSDOOH, OUTPUT SOURCE CURRENT (mA) Figure 10. Typical SDO Output Sink Characteristics Figure 11. Typical SDO Output Source Characteristics Communication Controller Interface Termination 5 It is recommended to use a transmission line series termination in order to overcome these problems. A series termination comprises of a resistor between the driver’s output and the transmission line. The signals of the communication controller (CC) interface (TxD, TxEN and RxD) achieve high enough speed that the PCB connection should be considered a transmission line. The CMOS driver’s impedance can be significantly lower than the PCB track characteristic impedance Z0, depending on the PCB configuration. The impedance mismatch at the ends of the line may cause reflections and thus all kinds of overshoots and undershoots. This may lead to signal integrity problems and increased electromagnetic emissions. A typical PCB configuration is shown in the Figure 12 and Figure 13. An estimated characteristic impedance of the given 8 mils wide TOP layer trace is ca. 130 W at 2−Layer PCB (Figure 12) and ca. 72 W at 4-Layer PCB (Figure 13). http://onsemi.com 4 AND9148/D w = 8 mils (0.2032 mm) t = 1 oz (35 μm) Trace h = 60 mils (1.524 mm) Dielectric (FR−4, er =4.6) Ground Plane Figure 12. Example of 2−Layer PCB Signal Traces TOP Ground Plane 10 mils (0.254 mm) Dielectric(FR−4, er =4.6) 40 mils (1.016 mm) Power Plane Signal Traces BOTTOM 10 mils (0.254 mm) Figure 13. Example of 4−Layer PCB The series termination resistor Rs should by calculated as follows: Rs [ Line Z0*Driver impedance shown in the Figure 14. The TxD and TxEN signals are driven by an MCU or communication controller. An example of the TxD output driver of Freescale MC9S12XF MCU is shown in the Figure 15. (eq. 1) The line characteristic impedance Z0 [W] depends on the PCB configuration. Typical RxD driver output impedance is 50 TEMP = 25°C DRIVER OUTPUT IMPEDANCE (W) DRIVER OUTPUT IMPEDANCE (W) 50 40 30 Output High 20 Output Low 10 0 0 1 2 3 4 TEMP = 25°C 40 30 |IOH|, IOL OUTPUT CURRENT (mA) 1 2 3 4 5 Figure 15. Freescale MC9S12XF MCU TxD Pin Output Impedance Calculation example • 0 |IOH|, IOL OUTPUT CURRENT (mA) Figure 14. NCV7383 RxD Pin Output Impedance (typical) • Output Low 10 0 5 Output High 20 Ideal Series termination resistor value ≈ 72 W - 33 W = = 39 W Recommended value is 33 W. Inputs: 4-Layer FR-4 PCB (Figure 13), 8 mils trace with estimated characteristic impedance 72 W. RxD driver output impedance 33 W. http://onsemi.com 5 AND9148/D Figure 16. RxD Trace Impedance Mismatch Compensation (4−Layer PCB, ringing at MCU input pin) Figure 17. RXD Trace Impedance Mismatch Compensation (2−Layer PCB, ringing at MCU input pin) Design recommendations: • Place the RxD serial termination resistor close to transceiver. • Place the TxD and TxEN serial termination resistor close to microcontroller / Communication Controller. • Surface mount resistor is preferred in order to avoid additional serial inductance. • Maximum value of series termination resistance is limited by required signal rise/fall time. Particularly values higher than 33 W should be carefully considered. BP BM RCM1 RCM2 Unsupplied Normal Standby Sleep Bus Impedance in Power−off Mode Vcc/2 Figure 18. Simplified Bus Biasing Circuit In order not to disturb the rest of the FlexRay network in case NCV7383 is unsupplied, the bus lines BP and BM remain High−Impedant with maximum leakage current of 5ĂmA (see the iBPLEAK and iBMLEAK parameter). This is valid for bus common mode voltage range uCM = 0 V to 5 V (See the Figure 18 and Figure 19). http://onsemi.com 6 AND9148/D 1.5 BP = BM iBP, iBM INPUT CURRENT (mA) 1 0.5 0 −0.5 Standby Unsupplied: iBP LEAK, iBM LEAK = max 5mA −1 Unsupplied in range 0−5 V −1.5 −15 −10 −5 0 5 10 15 BP, BM COMMON MODE VOLTAGE (V) Figure 19. Bus Leakage Current versus Common Mode Voltage uCM Table 3. EXTRACT FROM THE DEVICE DATASHEET [1] Symbol Parameter Conditions Min Typ Max Unit 10 24 40 kW RCM1, RCM2 Receiver common mode resistance iBPLEAK iBMLEAK Absolute leakage current when driver is off uBP = uBM = 5 V All other pins = 0 V 5 mA iBPLEAKGND iBMLEAKGND Absolute leakage current, in case of loss of GND uBP = uBM = 0 V All other pins = 16 V 1600 mA REFERENCES [1] ON Semiconductor, NCV7383/D Datasheet, Rev.P1, January 2013 [2] FlexRay Consortium. FlexRay Communications System − Electrical Physical Layer Specification, V3.0.1, October 2010 [3] FlexRay Consortium. FlexRay Communications System − Physical Layer EMC Measurement Specification, V3.0.1, October 2010 [4] ON Semiconductor, NUP2115L/D, Datasheet, Rev.0, April 2013 All brand names and product names appearing in this document are registered trademarks or trademarks of their respective holders. ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). 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