NCV7691RCLEVB Advance Information NCV7691 8-Channel Rear Combo / Daylight Running Light Evaluation Board User'sManual www.onsemi.com EVAL BOARD USER’S MANUAL Introduction Evaluation Board Features • Wide Range of Supply Voltage: 7 to 40 V • Eight LED Strings with On−board Red or White LEDs The evaluation board demonstrates rear combination / daylight running light (RCL/DRL) solution with up to eight LED string. The board regulates constant current of 100 mA (68 to 150 mA) through each on−board LED string consisting of three red or two white LEDs in the wide range of the supply voltage. The current is reduced for the board temperature above 90°C. The board is designed in order to provide good cooling of the active components with no extra cost. Additionally, a heat sink may be mounted on the bottom side of the board to improve the thermal capability of the board. In case of LEDs short or opening, the current sources are disabled and the fault may be detected by the ECU diagnostics. On−board LEDs may be easily replaced by external ones. (RCL/DRL) • Nominal LED Current 100 mA (150 mA max.) • Over−temperature Current Fold−back Protection • OPEN Jumper in each String Allowing LEDs • • • • • • • Disconnection SHORT Jumper in each String for Short Emulation or Connection of the External LEDs Led Short−circuit and Open−load Emulation Jumpers Optional External PWM Input Optional Error Flagging through Indication LED and FLTS Output Positions for Optional EMC Capacitors One−side Components Assembly Passive Cooling (Optional Heat Sink may be Attached to the Bottom) Figure 1. Running NCV7691 Evaluation Board Picture This document contains information on a new product. Specifications and information herein are subject to change without notice. © Semiconductor Components Industries, LLC, 2015 May, 2015 − Rev. P0 1 Publication Order Number: EVBUM2299/D NCV7691RCLEVB Table 1. ABSOLUTE MAXIMUM RATINGS Rating Value Unit −40 to +40 V 150 mA −0.3 to Vbat V 0 to 200 mA Junction Temperature (NCV7691, BCP56) −40 to +150 °C Junction Temperature (ASMT−QRBD−AEF0E, ASMT−QWBF−NKL0E) −40 to +125 °C Ambient Temperature −40 to +105 °C Supply Voltage (Vbat) LED String Current (thermally limited) PWM, FLTS, Err Voltage (J1 connector) Error pin current (J1 connector, pin 3) Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality should not be assumed, damage may occur and reliability may be affected. Table 2. RECOMMENDED BOARD OPERATING CONDITIONS Rating Supply Voltage (Vbat) Rated LED string Current (VS < 18 V, Tboard < +90°C) Open−Load or Short−Circuit board consumption (VS = 14 V) Ambient Temperature (for rated LED current) www.onsemi.com 2 Value Unit 7 to 18 V 68 /100 /150 mA max. 7 mA −40 to +70 °C NCV7691RCLEVB REAR COMBO / DAYLIGHT RUNNING LIGHT EVALUATION BOARD SCHEMATIC Figure 2. NCV7691 RCL/DRL Evaluation Board Schematic www.onsemi.com 3 NCV7691RCLEVB Table 3. INTERFACE FUNCTION DESCRIPTION Connector Name Connector Type VBAT 2.1 mm DC supply Description / Function OPEN1−8 SMD Jumper Removing the jumper emulates open LED condition SHORT1−8 SMD Jumper Shorting terminals by the jumper emulates short LED condition OR terminal for external LEDs B Test Point BASE output of NCV7691 / NPN base Col1 Test Point String 1 NPN collector Col5 Test Point String 5 NPN collector FB Test Point FB output of NCV7691 FB1 Test Point String 1 NPN emitter / feedback resistor FB5 Test Point String 5 NPN emitter / feedback resistor J1 SMD Header Supply battery input Control/diagnostic functions: Pin 1: GND Pin 2: PWM input (10k pull−up to VS) Pin 3: Error signal (active low, pull−up to VS through LED and 10k) Pin 4: FLTS pin of NCV7691 Pin 5: Alternative pull−up input for the error signal (if used, remove R9’) GETTING STARTED be connected through SHORT header while on−board LEDs are disconnected. The LEDs current is defined by Rx1 resistors. By default, it is set to 100 mA, but may be changed using following formula: • With no thermal fold−back (NTC pin grounded): The board is supplied through a standard 5.5 x 2.1 mm DC connector. Nominal supply voltage ranges from 7 to 18 V. Below 7 V, the current through the LEDs starts decreasing. For battery voltage above 18 V, the LED current is reduced by the over−voltage fold back to reduce the power dissipation. The thermal fold−back circuitry ensures the board temperature remains within the safe range (see following chapter for details). Two jumpers in each string emulate LEDs short or opening. By default, OPEN jumper is closed while SHORT terminals are not shorted. Alternatively, external LEDs may R1 + FB Regulation Voltage [ 0.15 I LED I LED • With thermal fold−back circuitry on NTC pin: R1 + V NTC [ 1.5 + 0.15 10 @ I LED 10 @ I LED I LED 7 to 18 V 2.1 mm DC supply LED current programming resistors Thermal fold−back circuitry NCV7691 Positions for optional EMC resistors Figure 3. NCV7691 8−channel Evaluation Board Picture www.onsemi.com 4 NCV7691RCLEVB Modules Control Strategy diagnosis of the failure on the LED module (open load or short−circuit) (see Figure 3). In case of both LED short and disconnection, NCV7691 disables all the NPN bipolars. In decentralized operation, extra wires are needed for the control and diagnosis (Figure 4). For this purpose, header J1 is available on the board for easy access to FLTS and PWM functions of NCV7691. The board is designed to operate in standard “One Wire Driver Body ECU” and decentralized architecture. In the first case, both control and diagnosis is done through one supply wire. The dimming might be provided through the PWM applied to the High−side SmartFET in the body ECU. At the same time, the SmartFET allows Normal operation LED string open LED string short ECU ECU ECU control diagnostics control diagnostics NCV8460A control 7 mA max. @ 14 V 0.8 A RCL / DRL RCL / DRL NCV8460A 7 mA max. @ 14 V RCL / DRL open 8x 100 mA NCV7691 diagnostics NCV8460A short NCV7691 NCV7691 Figure 4. Centralized One Wire System Diagram www.onsemi.com 5 NCV7691RCLEVB Normal operation LED string open LED string short ECU ECU ECU Control / diagnostics Control / diagnostics Control / diagnostics error RCL / DRL error RCL / DRL RCL / DRL open NCV7691 short NCV7691 NCV7691 Figure 5. De−centralized System Diagram Open LED String Diagnostics One of the ways to improve the open load detection capability is more precise external BASE current limitation. An example of the circuit with one extra resistor and PNP bipolar is shown in Figure 6. NCV7691 includes Open Load Detection feature. When the LED is open, the control loop tries to increase the BASE current to reach 152 mV on the FB pin. As the BASE current is limited to typ. 25 mA, the FB voltage drops below the target level. When the FB voltage decreases below the Open Load Detection FB Threshold (typ. 75 mA), an open load is detected after a period defined by a capacitor connected to the FLTS pin. Figure 6 demonstrates an open load situation on two−string application. BCP56 ~ 9.3mA ~ 0.1mA NCV7691 ~ 10mA 45mV max. SC ~ 0.2mA BCP56 25mA 60mA 1R5 GND 1R5 1R5 10.9mA 57.3mV GND BC856 24.8mA V(FB) < 75 mV −> −> FLTS current source active −> −> LEDs off Figure 7. Improved Open Load Detection for 8 Strings BASE FB 14mV BASE 37.2mV 1R5 30mA FB 90mV NCV7691 SC BCP 56 ~ 24.8mA 47R BCP56 63.6mV V(FB) < 75 mV −> −> FLTS current source active −> −> LEDs off Short LED Diagnostics NCV7691 contains a LED string short detection based on LED string voltage measurement (pin SC). In case the voltage difference between the VS and SC pins drops below typ. 2 V (Figure 7), the BASE is switched off and FLTS current source is active to flag an error. In multi−string applications, an OR−circuitry (e.g. diodes) has to be used to cover all the strings. Figure 6. Open Load Detection Principle In multi−string applications with high−beta transistors, the feedback voltage from individual strings is averaged, so one defective LED string does not always lead to the open load detection. www.onsemi.com 6 NCV7691RCLEVB used for temperature sensing. For temperatures below the PTC sensing temperature, the thermistor has low resistance (typ. 470 W), so the circuitry output voltage is given by R4 and R5 while for high temperatures the reference voltage drops rapidly (Figure 9). R6 ensures the voltage on NTC input does not fall below the NTC Detection Level (max. 300 mV) at high temperature, which would result into a switch−over to the internal voltage reference of NCV7691. VS V(SC) > (VS −2 V) −> −> FLTS current source active −> LEDs off VS−0.5V BCP 56 BCP 56 NCV7691 1R5 SC 4.3 V 4.3 V 1R5 BASE FB GND R4 100 k T < Tsense R4 100 k R6 560 k PTC ~ 470 R R6 560 k R5 51k Figure 8. Short LED Detection Principle Thermal Considerations of the Board 1.45 V to NTC pin T >> Tsense PTC ³ R 0.31 V to NTC pin V(NTC) has to be > 0.3 V R5 51k Figure 10. Thermal Fold−back Circuitry at Low/High Temperature As the board dissipation is typ. 11 W at 13.8 V battery supply and 100 mA LED current, the thermal aspects should be taken into account for the board design. The main limitations are LED lifetime vs. operating temperature and NPN bipolar maximum junction temperature. The board was designed to operate at full current with board temperature of up to 90°C on standard 70 mm FR4 PCB substrate and passive cooling without any extra thermal improvements. In case higher power dissipation is foreseen, a cooling metal profile may be mounted to the bottom side of the board. The optimal Zener voltage in terms of the temperature independency is usually between 4 and 5 V. At the same time, it should be as low as possible to allow a low−battery operation. 4V7 Zener diode is recommended as a good tradeoff. Because of lower bias current (< 1 mA) and impedance of the Zener, the reference voltage is lower than the nominal one (∼4.3 V for 4V7 Zener) (Figure 10). Thermal Fold−back To the protect power dissipating devices on the board (LEDs, NPN bipolar transistor), a circuit reducing LED current at high board temperatures is included (Figure 8). VS R3 10k ~ 4.3 V R4 100 k Temperature dependent element Voltage reference 4V7 R6 560 k PTC Figure 11. NTC Voltage vs. Supply Voltage (Tpcb = 255C) to NTC pin R5 51k T < Tsense: 470 Ω T = Tsense + 15°C: >40 kΩ The sensing temperature (PTC parameter) has to be chosen carefully with respect to the heat distribution over the board and thermal properties of the power dissipating components. For PTC type B59641A95A62, the current fold−back reduces the reference voltage on the NTC pin and Figure 9. Thermal Fold−back Circuitry The circuit consists of a voltage reference (ZD1 supplied via R3) and temperature dependent resistor divider. A thermistor with positive temperature dependency (PTC) is www.onsemi.com 7 NCV7691RCLEVB thus LED current above the board temperature of ∼90°C (Figure 11). If the thermal fold−back feature is not required, components R3, R4, R6, ZD1 and PTC do not need to be assembled and NTC pin should be tied to GND (directly or via R5). EMC recommendations If extensive EMC immunity level is required, Cx1, C3 and C4 capacitors can improve the EMC performance. Using C3 is usually sufficient against disturbances from the supply line. Capacitors Cx1 and C4 may further improve the performance esp. in the setups with external (off−board) LEDs. Figure 12. NTC Voltage vs. Board Temperature (VS = 12 V) PCB DRAWINGS Assembly Drawings Figure 13. NCV7691 RCL EVB PCB Top Assembly Drawing (Red LEDs) Option A Figure 14. NCV7691 DRL EVB PCB Top Assembly Drawing (White LEDs) Option B www.onsemi.com 8 NCV7691RCLEVB Composite Drawings Figure 15. NCV7691 RCL/DRL EVB PCB Top Composite Drawing Figure 16. NCV7691 RCL/DRL EVB PCB Bottom Composite Drawing REFERENCES [3] ON Semiconductor, BCP56 NPN Silicon Epitaxial Transistor, Rev. 10, March, 2014. [1] ON Semiconductor, NCV7691 Product Datasheet Rev. 2, January 2015 [2] EPCOS, PTC thermistors as limit temperature sensors, Series: B59421, B59641, B59721, March 2014 ON Semiconductor and the are registered trademarks of Semiconductor Components Industries, LLC (SCILLC) or its subsidiaries in the United States and/or other countries. SCILLC owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. 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