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Automotive relay replacement evaluation board

Posted: 08 Dec 2000     Print Version  Bookmark and Share


Prepared by Philippe Perruchoud Motorola Applications Engineer Toulouse, France An Automotive Relay Replacement Board driven by an HC11 microprocessor is presented here.

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1MOTOROLA AN1678 Automotive Relay Replacement Evaluation Board Prepared by Philippe Perruchoud Motorola Applications Engineer Toulouse, France An Automotive Relay Replacement Board driven by an HC11 microprocessor is presented here. It is intended to run lamps and solenoids in an automotive environment with nominal voltages in the range of 12 V. Figure 1. Relay Replacement Evaluation Board INTRODUCTION The penetration of electronics in the automotive industry started some 15 years ago with electronically controlled powertrain systems, mainly driven by regulatory legislation. Today, occupant safety is enhanced with ABS systems and airbags requiring even more complex electronics. This penetration is still growing as we see the rise of another wave of electronics driven by consumers willing to personalize their daily driving experience in 3 key areas: comfort, security and driver identification. These areas require components with high reliability, new features, diagnostic functions, etc., but these changes require vehicle architecture modification as well as load control improvement. Mechanical relays are unable to perform certain desired functions such as soft turn on and turn off of motors, or dim- ming of incandescent loads. Improvement in semiconductor technologies and in package development now make pos- sible a conversion from a mechanical relay to an electronic driver which can offer more functionality, higher reliability and system cost reduction. Features like current limitation can be implemented easily on an electronic relay, allowing fuse elimination and wiring diameter reduction. Self-protection such as short circuit shut- down or over-temperature shutdown increase the reliability of the relay, and diagnostic functions such as open load detec- tion let the user know when the load is disconnected or dam- aged. Other advantages of the electronic relay over the mechani- cal relay are its smaller size, reduced weight and the elimina- tion of acoustic noise. Electronic relays generate less heat than mechanical relays. The Automotive Relay Replacement Board shown in Figure 1 was developed to demonstrate and evaluate mem- bers of a new product family designed to replace mechanical relays. EVALUATION BOARD DESCRIPTION Overview The evaluation board is designed to drive automotive bulbs and solenoids. It is controlled by an HC11 microprocessor that can be programmed via an on board serial interface. The microcontroller delivered with the board is pre-programmed but can be re-programmed from a PC with the help of soft- ware. The user can select the different loads with the buttons at the bottom of the board -- see Figure 2. Order this document by AN1678/D MOTOROLA SEMICONDUCTOR APPLICATION NOTE ) Motorola, Inc. 1999 AN1678 2 MOTOROLA Figure 2. Evaluation Board Functions RELAY REPLACEMENT SWITCHES VOLTAGE REGULATOR RESET SERIAL INTERFACE DIAGNOSTIC LEDs CONTROL BUTTONS MICRO CONTROLLER The relay replacement drivers are on the right side of the board -- the Power Stage. They are surface mount Integrated Circuits soldered directly onto the PCB. Power Stage Description Three different products used in the Power stage are relay replacement dual high side drivers, namely: 7 2 MC33286DW: GEMINI 7 1 MC33288DH: FLASHER 7 1 MC33289DW: DHSS Each IC contains 2 silicon chips: a control die and a dual power die. The power die is a MOSFET with the drain con- nected to the Vbat line. The Source of the MOSFET is con- nected directly to the load. The heat generated by the ICs is dissipated via the PCB copper traces connected to the Vbat line. The total Vbat cop- per traces surface for the 4 products is close to 36 cm2. Following is a short description of each of the products. GEMINI: Dual High Side Driver for 21W bulb. The GEMINI has the following features: 7 35 m Rdson max. at 250C 7 Breakdown Voltage greater than 40 V 7 Current limitation 7 Open load detection in the On state 7 Overtemperature shutdown with hysteresis 7 Under voltage shutdown 7 Separate diagnostic output 7 Reverse battery protection 7 Very low standby current (less than 1 5A) Figure 3. GEMINI Application Block Diagram CHANNEL 1 U.V. Lockout CHANNEL 2 Charge Pump Over Temp Open Load Input Trigger Over Current MCU Thermal Sensor Vbat VbatVbat Vbat Vbat VbatVbat Vbat Battery OUT2s OUT2 OUT2 Load 2 Status pull-up resistors 5V 10KW 10KW Status 2 IN2 IN1 Status 1 Vbatc GND OUT1 OUT1 OUT1s 21W AN1678 3MOTOROLA The GEMINI package is an SO20WB with a thermally en- hanced leadframe to enable maximum power dissipation through the 8 leads that are connected to Vbat copper traces. On the evaluation board, two GEMINI are used. The first one is used to drive two 21W rear lamps. The second GEMINI is used to drive a single 55W head-lamp with its dual output transistor channels configured in parallel. FLASHER: Dual Solid State Relay for Blinker Applications. The FLASHER has the following features: 7 25 m Rdson max. at 250C 7 1.2W per channel Warning lamp Driver 7 Breakdown Voltage greater than 40 V 7 Current limitation 7 Current recopy function 7 Open load detection in the On state 7 Overtemperature shutdown with hysteresis 7 Under-voltage shutdown 7 Common diagnostic output 7 Reverse battery protection 7 Low standby current (less than 5 5A) Figure 4. FLASHER Application Block Diagram VBATC IN-L IN-H MCU I/O I/O I/O A/D ST CUR R 5 V WARNING SWITCH TURN SWITCH DASHBOARD DIRECTION INDICATOR BUZZER MC33288 Static Flasher VBATP OUT-L 21W21W 5W DASHBOARD TRAILOR INDICATOR WLP 1.2 W OUT-R 21W21W 5W + - 21W 5W The FLASHER package is an HSOP20 with a copper heat- sink. The thermal resistance from Junction to Case is as low as 20C/W. On the evaluation board the thermal resistance from junction to ambient is lower than 250C/W, which permits three 21W plus two 5W bulbs to be driven by each channel. DHSS: Dual High Side Switch for inductive loads such as solenoid valves. The DHSS has the following features: 7 40 m Rdson max. at 250C 7 Breakdown Voltage greater than 40 V 7 Latched Current limitation 7 Open load detection in the Off state 7 Overtemperature shutdown with hysteresis 7 Under-voltage shutdown 7 Separate diagnostic output 7 Reverse battery protection 7 Very low standby current (less than 5 5A) AN1678 4 MOTOROLA Figure 5. DHSS Application Block Diagram CHANNEL 1 U.V.&O.V Lockout CHANNEL 2 Charge Pump Over Temp Open Load Input Trigger Over Current MCU Thermal Sensor Vbat VbatVbat Vbat Vbat VbatVbat Vbat Battery OUT2s OUT2 OUT2 Load 2 Status pull-up resistors 5V 10KW 10KW Status 2 IN2 IN1 Status 1 Vbatc GND OUT1 OUT1 OUT1s LOAD OLDE The DHSS is in an SO20WB package. On the evaluation board, one output channel of the DHSS is used to drive a sole- noid valve. Control Stage Description The control of the power products is performed with an MC68HC811E2 microcontroller. This microprocessor receives the user's commands through the push buttons and the potentiometer, then processes the information and pro- vides the control signals to the power devices. The microcontroller sends a 2 KHz PWM signal to the DHSS to control the valve. The position of the valve is a function of the duty cycle applied to the signal. The user controls the duty cycle with the potentiometer on the left side of the control switch panel. The microprocessor also generates the low PWM frequency for the blinker and the rear lamps. The blinker frequency is 1.5 Hz with a 50% duty cycle. For the 21W rear lamps, a 100 Hz PWM frequency (undetectable to the human eye) is used with a 25% duty cycle to simulate a 5W bulb. During braking, the GEMINI turns the 21W rear bulbs on continuously. Finally, the control stage scans the status output of each driver. If any problem appears, the LED corresponding to the failed device is turned on. For the blinker function, a complex "failed lamp detection" that is detailed below is implemented based on the current recopy function of the FLASHER device. The DHSS fault detection latches off the faulted output. To get the DHSS to function again, just press the RESET button located in the top central area of the board. For one second following the RESET, the FLASHER device is turned on to calibrate the "failed lamp detection" function. If no load is connected to the FLASHER output, it will detect an open load, and the fault LED will be turned on. AN1678 5MOTOROLA Programming the Microcontroller As mentioned above, a serial interface was implemented on the evaluation board so that you can modify the program or write your own program to control the power devices. Along with the board a floppy disk entitled "Relay Replacement Eval- uation Board Program" is supplied. It contains the source code and the files necessary to down load the program from the PC to the microcontroller. You will need a PC with WINDOWS 3.11 operating system and the PCBUG11 software, a power supply (12 volts/15 Amps), and an RS232 cable to link the computer to the board in order to establish the communication. To download the soft- ware: 1. Connect the power supply and the RS232 cable to the board using the instructions given in the next section titled "Connector pin to pin description" (Make sure that there is no other application working on the port selected) 2. Put the microprocessor in the Bootstrap mode -- this means MODA and MODB wired to Vss. 3. Turn on the power supply and press the RESET button. 4. Then start PCBUG11 up with the command: pcbug11.exe 5. Choose the appropriate options to configure the microprocessor: -- Talker: no -- XIRQ interrupt: no -- Choice of the microprocessor: 4 -- Program directly a macro: no -- Port used for the application: (1 or 2) -- Internal clock 8 MHz: yes 6. If the communication is correctly established you are now ready to program the microprocessor. If there is no communication between the computer and the evaluation board, verify the instructions were performed in the right order. Check the RS232 cable connection on the board side (pins 4 and 7 should be +10 V and *10 V respectively) and then type "restart" in the command window of PCBUG11. Be careful: There must be no other application running on the port chosen for the communication.If there is still no response after doing this, turn off your computer and try again. 7. To start downloading the program, type the following instructions: eeprom $f800 $ffff loads a:\ loads a:\relay.s19 8. To execute the program, put the switches back to their original position: MODA wired to Vss and MODB to Vdd. Connector Pin to Pin Description The power supply and all the loads can be hooked up to the evaluation board via the screw connector on the right side of the board. BAT: Vbat supply voltage source input. All the power devices are connected to the Vbat rail, which corresponds to the battery voltage in the automotive application. Two screw connectors are used for the Vbat line due to the high peak cur- rents during lamp inrush current. The nominal current when all products are running fully loaded is around 15 A. Transient current can reach up to 50 or 60 A. A 470 5F capacitor (C16) is placed between the Vbat rail and the Ground rail and allows up to 10m of wire connection between the evaluation board and the actual Vbat power supply in most of the test configura- tions. The microcontroller is also supplied by the Vbat rail through a 5 V voltage regulator on the top left side of the board. GND: The Ground is common to the controller ground and the control pins of the power devices. No high current should normally flow through the GND except during the free- wheeling period of the valve when the DHSS is on. Figure 6. Connector Pinout RRL1 LRL2 LBL3 WLP4 RBL5 VAL6 GND7 BAT8 BAT9 HLP10 RRL: Right Rear Lamp. A 21W bulb can be connected to this output. This output is driven by the GEMINI right side (U9). LRL: Left Rear Lamp. A 21W bulb can be connected to this output, which is driven by the GEMINI left side (U9). RBL: Right Blinker Lamp. Three 21W bulbs and two 5W bulbs can be connected to this output (Car + Trailor). This out- put is driven by the FLASHER right side (U7). LBL: Left Blinker Lamp. Three 21W bulbs and two 5W bulbs can be connected to this output (Car + Trailor). This output is driven by the FLASHER left side (U7). WLP: Warning Lamp. A 1.2W dash board lamp can be con- nected to this output. It is turned on during the warning mode. This output is driven by the FLASHER Wlp output (U7). HLP: Head Lamp. A 55W lamp is to be connected to this output which is driven by the two paralleled outputs of the GEMINI (U8). VAL: Valve. The DHSS (U6) can drive an automotive valve with a nominal current of 1 to 2 A. AN1678 6 MOTOROLA Jumper Description J1: This jumpers is used to determine the mode of the applica- tion: single ship mode if we want to execute the program, and bootstrap mode to program the microprocessor. J2: This is linked to the XIRQ* pin and is only used for the external interrupts. J3: This jumper is linked to the IRQ* pin and it is not used in our application. J4: This is not a jumper, but a test pin to detect a communica- tion failure between the computer and the board. APPLICATION DIAGRAMS An application example shown in Figure 7 illustrates con- nections to the evaluation board and the loads. Cable connec- tions for the PC and the load connection are not supplied with the evaluation board. The board is fully protected against short circuit to ground and reverse battery conditions. In case of short circuit, some of the power devices can get very hot before they go into ther- mal shutdown. In case of reverse battery, the power MOSFETs are turned on. In this condition, the loads are likely to conduct current. Figure 7. Application Example RRL LRL LBL WLP RBL VAL GND BAT BAT HLP Relay Replacement PC with Windows 3.11 Evaluation Board RS232 AN1678 7MOTOROLA Boards contents are described by the following schematic and parts list. Table 1. Parts List AAAAAAAAAAAA Item AAAAAAAAAAAA Quantity AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA Reference AAAAAAAAAAAAAA Part AAAAAAAAAAAA 1 AAAAAAAAAAAA 6 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA R1,R2,R3,R4,R29,R36 AAAAAAAAAAAAAA 470 Ohms AAAAAAAAAAAA 2 AAAAAAAAAAAA 19 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA R5,R6,R7,R8,R9,R10,R12,R13,R16,R17,R20,R21,R22,R23,R24, R25,R26,R27,R34 AAAAAAAAAAAAAA 10 kOhms AAAAAAAAAAAA3 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAR11 AAAAAAAAAAAAAA680 Ohms AAAAAAAAAAAA4 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAR14 AAAAAAAAAAAAAA270 kOhms AAAAAA AAAAAA5 AAAAAA AAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAR15 AAAAAAA AAAAAAA100 kOhms AAAAAA AAAAAA6 AAAAAA AAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAR18 AAAAAAA AAAAAAA10 MOhms AAAAAA AAAAAA7 AAAAAA AAAAAA4 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAR19,R30,R32,R33 AAAAAAA AAAAAAA1 kOhms AAAAAAAAAAAA8 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAR28 AAAAAAAAAAAAAA4,7 kOhms AAAAAAAAAAAA9 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAR31 AAAAAAAAAAAAAA2,2 kOhms AAAAAAAAAAAA10 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAR35 AAAAAAAAAAAAAA100 Ohms AAAAAAAAAAAA11 AAAAAAAAAAAA2 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAC1,C2 AAAAAAAAAAAAAA22 pF AAAAAA AAAAAA12 AAAAAA AAAAAA3 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAC3,C5,C7 AAAAAAA AAAAAAA10 nF AAAAAA AAAAAA13 AAAAAA AAAAAA3 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAC4,C6,C11 AAAAAAA AAAAAAA0,1 uF AAAAAA AAAAAA14 AAAAAA AAAAAA2 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAC8,C9 AAAAAAA AAAAAAA0,47 uF AAAAAAAAAAAA15 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAC10 AAAAAAAAAAAAAA47 nF AAAAAAAAAAAA16 AAAAAAAAAAAA4 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAC12,C13,C14,C15 AAAAAAAAAAAAAA1 uF AAAAAAAAAAAA17 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAC16 AAAAAAAAAAAAAA470 uF Chimic AAAAAAAAAAAA18 AAAAAAAAAAAA2 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAZ1,Z2 AAAAAAAAAAAAAAZener 6,3 V AAAAAAAAAAAA19 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAPOT AAAAAAAAAAAAAA10k AAAAAAAAAAAA20 AAAAAAAAAAAA3 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAD1,D2,D3 AAAAAAAAAAAAAADiode 1N4001 AAAAAAAAAAAA21 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAADiodeRL AAAAAAAAAAAAAASchotcky diode AAAAAAAAAAAA22 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAP1 AAAAAAAAAAAAAADB9 AAAAAAAAAAAA23 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAP2 AAAAAAAAAAAAAAScrew Terminal AAAAAA AAAAAA24 AAAAAA AAAAAA4 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAALED1,LED2,LED3,LED4 AAAAAAA AAAAAAALeds AAAAAA AAAAAA25 AAAAAA AAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAQUARTZ AAAAAAA AAAAAAA8 MHz AAAAAA AAAAAA26 AAAAAA AAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAU1 AAAAAAA AAAAAAAMC68HC811E2 AAAAAA AAAAAA27 AAAAAA AAAAAA2 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAU2,U3 AAAAAAA AAAAAAAOpto 4N32 AAAAAAAAAAAA28 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAU4 AAAAAAAAAAAAAAMC34064P AAAAAAAAAAAA29 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAU5 AAAAAAAAAAAAAARectifier Bridge AAAAAA AAAAAA30 AAAAAA AAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAU6 AAAAAAA AAAAAAAMC33289 AAAAAA AAAAAA31 AAAAAA AAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAU7 AAAAAAA AAAAAAAMC33288 AAAAAAAAAAAA32 AAAAAAAAAAAA2 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAU8,U9 AAAAAAAAAAAAAAMC33286 AAAAAAAAAAAA33 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAU10 AAAAAAAAAAAAAAMC7805CT AAAAAAAAAAAA34 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAJ1 AAAAAAAAAAAAAAJumper AAAAAAAAAAAA35 AAAAAAAAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAJ2 AAAAAAAAAAAAAAJumper AAAAAA AAAAAA36 AAAAAA AAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAJ3 AAAAAAA AAAAAAAInterrupt pin AAAAAA AAAAAA37 AAAAAA AAAAAA1 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAJ4 AAAAAAA AAAAAAATest pin AN1678 8 MOTOROLA Figure 8. 47 48 49 50 51 52 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 VDD VDD RIGHT BLINKER BRAKES WARNING SIDE LIGHT LEFT BLINKER HEAD LIGHT R27 10 k R26 10 k R25 10 k R24 10 k R23 10 k R22 10 k R5 10 k R10 10 k C10 47 nF6.3 V Z2 VBAT PB3 PB2 PB1 PB0 PE1 BP6 BP5 BP4 BP3 BP2 BP1 VDD VDD LED1 LED2 LED3 LED4 GND R28 4.7 k DB9 P1 GND VDD D1 GND C9 0.47 mF R32 1.0 k MC34064P 2 4 1 RESET D2 6 4 1 3 BRIDGE AC AC + - GND R36 470 R C8 0.47 mF R31 2.2 k U5 PC4 PC5 PC6 PC7 R1 470 R R2 470 R R3 470 R R4 470 R J4 R29 PA5 VDD R18 10 M 1 2 3 4 5 6 4 5 6 1 2 3 U2 U3 QUARTZ C2 22 pF C1 22 pF 8 MHz VDD VDD R33 1.0 k J1 C5 10 nF C3 10 nF R15 100 k R20 10 k C7 10 nF Z1 6.3 V C4 0.1 mF OPTO 4N35 OPTO 4N35 PD0 IRQ* XIRQ* RESET* PC7 PC6 PC5 PC4 PC3 PC2 PC1 PC0 XTALPE5 PE1 PE4 PE0 PB0 PB1 PB2 PB3 PB4 PB5 PB6 PB7 PA0 J3 R19 1.0 k POT 10 k EXTAL STRB E STRA MODA MODB VSS Vrh Vrl PE7 PE3 PE6 PE2 PD1 PD2 PD3 PD4 PD5 VDD PA7 PA6 PA4 PA3 PA2 PA1 PA5 R30 1.0 k R34 10 k R35 100 R J2 5 9 4 8 3 7 2 6 1 U1 68HC811E2FN U4 R14 270 k AN1678 9MOTOROLA Figure 9. VBAT VBAT OUT1 OUT1 VBAT VBAT OUTS1 IN1 ST1 VBATC VBAT VBAT OUT2 OUT2 VBAT VBAT OUTS2 IN2 ST2 GND 20 19 18 17 16 15 14 13 12 11 1 2 3 4 5 6 7 8 9 10 VBAT VBAT OUT1 OUT1 VBAT VBAT OUTS1 IN1 ST1 VBATC VBAT VBAT OUT2 OUT2 VBAT VBAT OUTS2 IN2 ST2 GND 20 19 18 17 16 15 14 13 12 11 1 2 3 4 5 6 7 8 9 10 U9 GEMINI MC33286 U8 GEMINI MC33286 VBAT VBAT OUT1 OUT1 VBAT VBAT OUTS1 IN1 ST1 OLDE VBAT VBAT OUT2 OUT2 VBAT VBAT OUT2S IN2 ST2 GND 20 19 18 17 16 15 14 13 12 11 1 2 3 4 5 6 7 8 9 10 GND CUR R IN1 OUTS1 NC OUT1 OUT1 OUT1 NC NC WLP ST IN2 OUTS2 NC OUT2 OUT2 OUT2 NC NC 20 19 18 17 16 15 14 13 12 11 1 2 3 4 5 6 7 8 9 10 VBAT FLASHER MC33288 U6 DHSS MC33289 PC7 RBL R16 10 k R17 10 k VDD PC6 PB2 R12 10 k R13 10 k C12 1.0 mF LRL RRL VBAT C13 1.0 mF HLP VBAT VDD PC4 VBAT PB1 PC5 LBL VDD R21 10 k R7 10 k R9 10 k C10 47 nF R11 680 R 10 k R8 C14 1.0 mF U7 RBL PB0 PE1 VDD PC4 PA5 VAL 10 k R6 DiodeRL 1N4001 C15 1.0 mF C6 0.1 mF VDDU10 31 2 C16 470 mF C11 0.1 mF VSS MC7805CT + D3 1N4001 VBAT 21 AN1678 10 MOTOROLA Blinker Failed Lamp Detection It is important that the driver be warned whenever a bulb has failed. The difficulty of this function for the blinker application lies in the fact that the Flasher drives several bulbs simultaneously. The Flasher device features a current recopy function that allows the microcontroller to monitor load currents while the outputs are on. If the output current changes beyond a certain limit, the mi- crocontroller warns the driver that one of the blinker lamps is damaged by causing the working lamps to blink at double fre- quency. But in reality, it is not that simple. Tolerance in the measurementchain has to be taken into account as well as the load tolerances. Additionally, the load current varies with changes in the battery voltage. Therefore, accurate monitoring of the battery voltage is required by the microcontroller. Another error factor is the 5W vehicle side bulbs that can be on or off without altering the diagnostic result. The tolerance of the measurement chain is mainly due to the Flasher current recopy accuracy which is specified at 110% over the temperature range from -400C to +1250C. The 21W bulbs are specified at 16% accuracy and the 5W bulbs at 110%. With the given tolerance, a single 21W bulb failure out of two can be detected as described in Figure 10. LoadCurrent(A) 8 10 14 0 1 12 1.5 0.5 3 2 2.5 16 2*21W worse case 3.5 4 Battery Voltage (V) 2*21W+1*5W worst case Figure 10. Failed Lamp detection out of 2 lamps If a trailer is connected to the vehicle, the detection with absolute limits is no longer possible because the lower and the upper limits overlap. In the program developed for the evaluation board, we decided to implement a different approach based on a relative comparison. The idea is to be able to store the value of the load current in a non-volatile memory. Each time the system is turned on, the measured current is compared to the stored value. If the difference between the two values is below a certain percentage, the stored value will be refreshed. On the other hand, if the difference is above a certain limit, a failed bulb will be reported. Detecting a failed lamp on the trailer is also possible. The software compares the left and right channel currents. If it de- tects 3 bulbs on one side and 2 on the other, it will detect a failed bulb. The advantage of this relative approach is that the system adapts as it is modified over time, and with the part to part variation for each component of the measurement chain. The only limitation of this solution is that if the trailer is removed while the car is powered up (no RESET), the first time the blinker is on, the microcontroller will detect a failed bulb. This solution requires the storage of 2 values in a non volatile memory and a calibration the very first time the car is powered up. The micro used in our demonstration board is not capable of such a feature, and the calibration is done at every RESET. This is the reason why the blinker bulbs are turned on after every RESET. In the algorithm implemented in the evaluation board, any current recopy variation above 22% is considered a failure. CONCLUSION The Relay Replacement Evaluation Board is a tool allowing rapid evaluation of several different solid state relays developed by Motorola. Their thermal and electrical behavior can rapidly be analyzed before going further with PCB development. In addition, the board design can be used as a reference for speeding hardware development. AN1678 11MOTOROLA NOTES AN1678 12 MOTOROLA Motorola reserves the right to make changes without further notice to any products herein. Motorola makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does Motorola assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages. "Typical" parameters which may be provided in Motorola datasheetsand/orspecificationscananddovaryindifferentapplicationsandactualperformancemayvaryovertime. Alloperatingparameters,including"Typicals" must be validated for each customer application by customer's technical experts. Motorola does not convey any license under its patent rights nor the rights of others. Motorola products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applicationsintended to support or sustain life, or for any other application in which the failure of the Motorola product could create a situation where personal injury ordeath may occur. Should Buyer purchase or use Motorola products for any such unintended or unauthorized application, Buyer shall indemnify and hold Motorola and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that Motorola was negligent regarding the design or manufacture of the part. Motorola and are registered trademarks of Motorola, Inc. Motorola, Inc. is an Equal Opportunity/Affirmative Action Employer. Mfax is a trademark of Motorola, Inc. How to reach us: USA/EUROPE/Locations Not Listed: Motorola Literature Distribution; JAPAN: Motorola Japan Ltd.; SPD, Strategic Planning Office, 141, P.O. Box 5405, Denver, Colorado 80217. 1-303-675-2140 or 1-800-441-2447 4-32-1 Nishi-Gotanda, Shinagawa-ku, Tokyo, Japan. 81-3-5487-8488 Customer Focus Center: 1-800-521-6274 MfaxTM: - TOUCHTONE 1-602-244-6609 ASIA/PACIFIC: Motorola Semiconductors H.K. Ltd.; Silicon Harbour Centre, Motorola Fax Back System - US & Canada ONLY 1-800-774-1848 2, Dai King Street, Tai Po Industrial Estate, Tai Po, N.T., Hong Kong. - 852-26629298 HOME PAGE: AN1678/D

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