NCV7680 Linear Current Regulator and Controller for Automotive LED Rear Combination Lamps The NCV7680 consists of eight linear programmable constant current sources. The part is designed for use in the regulation and control of LED based Rear Combination Lamps for automotive applications. System design with the NCV7680 allows for two brightness levels, one for stop and one for tail illumination, or optional PWM control can also be implemented. Discrete LED brightness levels are easily programmed (stop current value, tail duty cycle value) optional external ballast FET allows for power distribution on designs requiring high currents. Set back power limit reduces the drive current during overvoltage conditions. This is most useful for low current applications when no external FET is used. http://onsemi.com MARKING DIAGRAM A WL YY WW G Features • • • • • • • • • • • • • Constant Current Outputs for LED String Drive LED Drive Current up to 75 mA per Channel Open LED String Diagnostic with Open−Drain Output Slew Rate Control Eliminates EMI Concerns Low Dropout Operation for Pre−Regulator Applications External Modulation Capable On−chip 1 kHz Tail PWM Dimming Single Resistor for Stop Current Set Point Single Resistor for Tail Dimming Set Point Overvoltage Set Back Power Limitation AEC Q100 Qualified 16 Lead SOICW Exposed Pad This is a Pb−Free Device V7680 AWLYYWWG SOIC−16 WB PW SUFFIX CASE 751AG = Assembly Location = Wafer Lot = Year = Work Week = Pb−Free Device ORDERING INFORMATION Device Package Shipping† NCV7680PWR2G SOIC−16WB (Pb−Free) 1000 / Tape & Reel †For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD8011/D. Applications • • • • • • Rear Combination Lamps (RCL) Daytime Running Lights (DRL) Fog Lights Center High Mounted Stop Lamps (CHMSL) Arrays Turn Signal and Other Externally Modulated Applications LCD Back Lighting © Semiconductor Components Industries, LLC, 2013 March, 2013 − Rev. 6 1 Publication Order Number: NCV7680/D NCV7680 VP Output Current Ballast Drive Regulation Control Out1 Ballast Drive Out2 FB Out3 + Out4 FET Drive - 1.05 V Out5 Out6 STOP Output Control Out7 DIAG Diagnostic Reporting (high reporting) Out8 GND Open Circuit Rstop Current Limit Overvoltage Set Back Current (down 20%) Current Programming RSTOP Figure 1. Simple Block Diagram http://onsemi.com 2 RTAIL NCV7680 VP Overvoltage − 100k FET Drive OUT2 OUT3 Overtemperature & Overvoltage sense Output Disable 1.05 V + − Control Logic Setback Current −20% DIAG Interface STOP 100 mV OUT5 OUT6 Open Circuit Detect 200k OUT4 + + 5V OUT1 Channel Control OUT7 − Soft Start, Bias, and Reference + FB 1 of 8 − Ballast Drive 400 mV OUT8 IRSTOP x 100 GND DIAG Oscillator and PWM V−I Converter Vreg Irstop 4.4 V − Pin Current Limit + 0.4 V RSTOP RTAIL Figure 2. Detailed Block Diagram OUT1 VP Ballast Drive FB STOP/PWM DIAG RSTOP RTAIL Rtail EP OUT2 OUT3 OUT4 GND OUT5 OUT6 OUT7 OUT8 Figure 3. Pinout Diagram http://onsemi.com 3 NCV7680 TAIL Input MRA4003T3G STOP Input MRA4003T3G C1 0.1mF VSTRING NTD2955 C3 100nF R3 1k C2 0.22mF R1 10k NCV7680 OUT2 OUT1 OUT3 VP Ballast Drive OUT4 FB GND STOP/PWM OUT5 R4, 3.09k C4 10nF DIAG OUT6 RSTOP OUT7 RTAIL OUT8 R5, 2.21k epad R6 8.87k Vref R1 limits the current out of STOP/PWM during reverse battery condition. R6 and R7 values shown yield 10.5 V regulation on VSTRING. C1 is for line noise considerations. C3 is for EMS considerations. R7 1k Figure 4. Application Diagram with External FET Ballast Transistor TAIL Input MRA4003T3G STOP Input MRA4003T3G C3 100nF R1 10k R8 10k NCV7680 OUT2 OUT1 OUT3 VP Ballast Drive OUT4 FB GND STOP/PWM OUT5 R4, 3.09k C4 10nF R5, 2.21k DIAG OUT6 RSTOP OUT7 RTAIL OUT8 epad Figure 5. Application Diagram without the FET Ballast Transistor When using the NCV7680 without the FET ballast transistor, tie the FB Pin to VP through a 10k resistor. http://onsemi.com 4 NCV7680 Table 1. APPLICATION I/O TRUTH TABLE (FB = Vref) (Reference Figure 2) Stop Input Tail Input OUTX Current (1−8) Fault State* DIAG State 0 0 OFF − HIGHZ** 1 0 ISTOP NORMAL LOW 1 0 ISTOP OPEN CIRCUIT*** HIGH** 0 1 PWM DO NOT CARE HIGH** 1 1 ISTOP NORMAL LOW 1 1 ISTOP OPEN CIRCUIT*** HIGH** * Open Circuit, RSTOP Current Limit, and Set Back Current Limit down 20% ** Pullup resistor to DIAG *** OPEN CIRCUIT = Any string open 0 = LOW 1 = HIGH TAIL STOP HIGHZ DIAG Open String Occurs Open String Removed Figure 6. DIAG Timing Diagram http://onsemi.com 5 Open String Occurs NCV7680 Table 2. PIN FUNCTION DESCRIPTION (16 Pin SO Wide Exposed Pad Package) Pin # Label 1 OUT1 Description Channel 1 constant current output to LED. Unused pin should be grounded. 2 VP 3 Ballast Drive Supply Voltage Input. 4 FB 5 STOP/PWM 6 DIAG 7 RSTOP 8 RTAIL Tail current duty cycle PWM program resistor. Ground if using external modulation. 9 OUT8 Channel 8 constant current output to LED. Unused pin should be grounded. 10 OUT7 Channel 7 constant current output to LED. Unused pin should be grounded. 11 OUT6 Channel 6 constant current output to LED. Unused pin should be grounded. 12 OUT5 Channel 5 constant current output to LED. Unused pin should be grounded. 13 GND Ground. 14 OUT4 Channel 4 constant current output to LED. Unused pin should be grounded. 15 OUT3 Channel 3 constant current output to LED. Unused pin should be grounded. 16 OUT2 Channel 2 constant current output to LED. Unused pin should be grounded. epad* epad Ground. Do not connect to pcb traces other than GND. Gate drive for external power distribution PFET. Ground if not used. Feedback Sense node for VP regulation. Use feedback resistor divider or connect to VP with a 10k resistor. Stop Logic Input. External Modulation Input. Open−drain diagnostic output. Reporting Open Circuit, RSTOP Current Limit, and Overvoltage Set Back Current down 20%. Normal Operation = LOW. Ground if not used. Stop current bias program resistor. *Grounding will provide better thermal and electrical performance. MAXIMUM RATINGS (Voltages are with respect to device substrate) Rating Value Unit VP, Ballast Drive, STOP, DIAG DC Peak Transient −0.3 to 45 45 Output Pin Voltage (OUTX) −0.3 to 45 V Output Pin Current (OUTX) 100 mA −0.3 to 5 V −40 to 150 °C 260 peak °C Input Voltage (RTAIL, RSTOP, FB) Junction Temperature, TJ Peak Reflow Soldering Temperature: Pb−Free 60 to 150 seconds at 217°C (Note 1) V Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect device reliability. 1. For additional information, see or download ON Semiconductor’s Soldering and Mounting Techniques Reference Manual, SOLDERRM/D, and Application Note AND8003/D. http://onsemi.com 6 NCV7680 Table 3. ATTRIBUTES Characteristics ESD Capability Value Human Body Model (RSTOP Pin) Human Body Model (All Remaining Pins) Machine Model Moisture Sensitivity Level > $1.8 kV > $2.0 kV > $200 V (Note 2) MSL 1 Storage Temperature −55°C to 150°C Package Thermal Resistance (Note 3) Junction−to−Board (RYJB) Junction−to−Ambient (RqJA) Junction−to−Pin (RYJL) 27°C/W 78°C/W 38°C/W Meets or exceeds JEDEC Spec EIA/JESD78 IC Latchup Test 2. For additional information, see or download ON Semiconductor’s Soldering and Mounting Techniques Reference Manual, SOLDERRM/D, and Application Note AND8003/D. 3. Values represent typical still air steady−state thermal performance on 1 oz. copper FR4 PCB with 650 mm2 copper area. ELECTRICAL CHARACTERISTICS (6 V < VP < 16 V, VSTOP = VP, RSTOP = 3.09 kW, RTAIL = 2.21 kW, −40°C v TJ v 150°C, unless otherwise specified) (Note 4) Characteristic Conditions Min Typ Max Unit − − − 6.5 6.4 6.0 8.0 8.0 8.0 31.5 30.8 35 35 38.5 39.2 mA 75 − − mA −7 −6 −5 0 0 0 7 6 5 % % % − 0.6 3.0 mA 0.3 0.4 0.5 V − 6.0 25 mA/us 16.0 18.7 24.5 V − 94 − %IOUT Diag Reporting of Set Back Current − 80 − %IOUT Output Disable Threshold − 100 250 mV − 4 0 5 10 − mA mA 0.95 1.05 1.15 V GENERAL PARAMETERS Quiescent Current (IOUTx = 35 mA) STOP Mode, 8 Channel VP = 16 V STOP Mode, 4 Channel VP = 16 V, OUT5 = OUT6 = OUT7 = OUT8 = GND Tail Mode VP = 16 V mA CURRENT SOURCE OUTPUTS OUTX = 1.0 V, TJ = 25°C, 150°C OUTX = 1.0 V, TJ = −40°C Output Current Maximum Regulated Output Current Current Matching −40°C 25°C 150°C ƪ ƪ 2I OUTx(min) I OUTx(min) ) I OUTx(max) 2I OUTx(max) I OUTx(min) ) I OUTx(max) Line Regulation ƫ ƫ *1 100 *1 100 6 V v VP v 16 V Open Circuit Detection Threshold Current Slew Rate IOUT = 35 mA, 10% to 90% Points Overvoltage Set Back Threshold @ 99% IOUT Overvoltage Set Back Current VP = 20 V FET DRIVER Ballast Drive Leakage Current Sink Current FB = 1.5 V, Ballast Drive = 3 V FB = 0.5 V, Ballast Drive = 3 V Ballast Drive Reference Voltage 4. Designed to meet these characteristics over the stated voltage and temperature recommended operating ranges, though may not be 100% parametrically tested in production. 5. Guaranteed by design. http://onsemi.com 7 NCV7680 ELECTRICAL CHARACTERISTICS (6 V < VP < 16 V, VSTOP = VP, RSTOP = 3.09 kW, RTAIL = 2.21 kW, −40°C v TJ v 150°C, unless otherwise specified) (Note 4) Characteristic Conditions Min Typ Max Unit Input High Threshold 1.6 1.9 2.2 V Input Low Threshold 0.7 0.85 1.1 V − 1.05 − V 0 150 300 mA 0.96 1.08 1.21 V − 100 − − − 1.8 2.2 mA STOP LOGIC VIN Hysteresis Input Bias Current STOP = 14 V PROGRAMMING RSTOP Bias Voltage Stop Current Programming Voltage RSTOP K multiplier IOUTX / IRSTOP RSTOP Current Limit RTAIL Bias Current Tail Duty Cycle Programming Current 300 350 450 mA Duty Cycle RTAIL = 0.59 V RTAIL = 1.21 V RTAIL = 3.29 V 3.5 17 59.5 5.0 20 70 6.5 23 80.5 % % % DIAG OUTPUT Output Low Voltage DIAG Active, IDIAG =1 mA − 0.1 0.40 V Output Leakage Current VDIAG = 5 V − − 10 mA THERMAL LIMIT Thermal Limit Temperature OUTx Reduction Initiated @ 99% IOUT (Note 5) 150 − − °C Thermal Shutdown (Note 5) 150 190 − °C Thermal Hysteresis (Note 5) − 15 − °C 4. Designed to meet these characteristics over the stated voltage and temperature recommended operating ranges, though may not be 100% parametrically tested in production. 5. Guaranteed by design. AC CHARACTERISTICS (6 V < VP < 16 V, VSTOP = VP, RSTOP = 3.09 kW, RTAIL = 2.21 kW, −40°C v TJ v 150°C, unless otherwise specified) Characteristic Min Typ Max Unit Stop Turn−on Delay Time VSTOP/PWM 90% to IOUTX 90% Conditions − 14 45 ms Stop Turn−off Delay Time VSTOP/PWM 10% to IOUTX 10% − 21 45 ms PWM Frequency STOP = 0 V 0.5 1.0 2.1 kHz Tail Frequency Stabilization Time VP step from 0 V to 6 V − 2.0 4.0 ms Open Circuit to DIAG Reporting − 4.0 10 ms http://onsemi.com 8 NCV7680 TYPICAL PERFORMANCE CHARACTERISTICS 160 qJA MAXIMUM (°C/W) 140 120 100 1 oz 80 2 oz 60 40 20 0 0 100 200 300 400 500 600 700 COPPER HEAT SPREADER AREA (2mm) Figure 7. qJA vs. Copper Spreader Area 1000 R(t) MAXIMUM (°C/W) 100 D = 0.5 0.2 0.1 10 0.05 0.02 0.01 1 SINGLE PULSE 0.1 0.000001 0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 100 1000 PULSE TIME (s) Figure 8. Thermal Duty Cycle Curves on 650 mm2 Spreader Test Board 1000 100 mm2 50 mm2 R(t) MAXIMUM (°C/W) 100 10 500 mm2 1 0.1 0.000001 0.00001 0.0001 0.001 0.01 0.1 1 PULSE TIME (s) Figure 9. Single Pulse Heating Curve http://onsemi.com 9 10 NCV7680 36 50 40 30 20 10 0 T = 25°C 0 0.5 1.0 1.5 2.0 2.5 3.0 4.0 4.5 35 34.5 34 33.5 5.0 60 50 50 40 30 20 80 100 120 140 160 3 4 6 5 7 8 9 40 30 20 10 RSTOP = 3.09 kW 2 60 40 Figure 11. IOUT vs. Temperature 60 1 20 Figure 10. IOUT vs. RSTOP 70 0 0 TEMPERATURE (°C) 70 0 RSTOP = 3.09 kW RSTOP (kW) 10 0 10 0 0.5 1 1.5 2 2.5 3 RTAIL (kW) V(RTAIL) Figure 12. Duty Cycle vs. RTAIL Figure 13. Duty Cycle vs. V(RTAIL) 3.5 40 35 RTAIL = 4 kW 30 DUTY CYCLE (%) 3.5 35.5 33 −40 −20 DUTY CYCLE (%) DUTY CYCLE (%) IOUT, OUTPUT CURRENT (mA) 60 IOUT, OUTPUT CURRENT (mA) IOUT, OUTPUT CURRENT (mA) 70 25 RTAIL = 3 kW 20 15 RTAIL = 2 kW 10 5 0 −40 −20 0 20 40 60 80 35 30 25 20 15 10 5 0 100 120 140 160 RSTOP = 3.09 kW 9 TEMPERATURE (°C) 11 13 15 17 19 21 VP (V) Figure 14. Duty Cycle vs. Temperature Figure 15. IOUT vs. VP http://onsemi.com 10 23 25 27 NCV7680 14 35.8 12 35.6 10 35.4 VSTRING (V) 35.2 35 34.8 34.6 6 per eq. 1 R7 = 1K 2 34.2 34 8 4 34.4 OUTX = 1 V 6 7 8 9 10 11 12 13 14 15 0 16 0 2000 4000 VP 6000 8000 R6 (W) Figure 16. VP Line Regulation Figure 17. VSTRING vs. R6 120 OUTx current is limited during short circuit events of RSTOP. The current rolls off per the diagram to prevent unexpected excessive power dissipation. 100 80 IOUT (mA) IOUTx, OUTPUT CURRENT (mA) 36 60 40 20 0 0 0.5 1.0 1.5 IRSTOP (mA) Figure 18. IOUT vs. IRSTOP http://onsemi.com 11 2.0 2.5 10000 12000 NCV7680 DETAILED OPERATING DESCRIPTION General reduced resulting in lower power dissipation on the IC. This occurs during high battery voltage (VP > 16 V). In this way the NCV7680 can operate in extreme conditions and still provide a controlled level of light output The Overvoltage condition is reported on the DIAG Pin. Reference Figures 19 and 20 for Power Limiting Behavior. The NCV7680 consists of eight linear programmable constant current sources. The part is designed for use in the regulation and control of LED based Rear Combination Lamps for automotive applications. System design with the NCV7680 allows for two brightness levels; one for stop, and one for tail illumination. Brightness levels are easily programmed (stop current absolute value, tail current duty cycle value) with two external resistors. The use of an external FET allows for power distribution on designs requiring high currents. Additionally, set back power limit reduces the drive current during overvoltage conditions. Set back power limit is most useful for low current applications when no external FET is used. The NCV7680 offers all of the built in protection normal to regulator systems, such as current limit, thermal limit, and provides an open load diagnostic that coincides with the STOP input signal. DRIVER POWER DISSIPATION Only Voltage Effects Low Drop−out Area Thermal Shutdown 180°C (typ) Constant Current Area Overvoltage Set Back Area IC POWER DISSIPATION Figure 19. Ballast FET Power Open String Reporting (DIAG) Open string detection is reported on the DIAG pin as a high with STOP Input high, or a combination of STOP Input high and TAIL Input high. Reference Table 1 on page 5 for more details. Open circuit is sensed on each of the 8 outputs. The typical threshold voltage for detection is 0.4 V. Care must be taken not to breach this voltage level under normal operation , or a false open will be reported. Make sure worst case system design focuses on the voltage level on top of the LED string (top anode) (VSTRING) and includes the worst case LED voltage drop while considering temperature effects. Low Drop−out Area Voltage Only Voltage Effects Constant Current Area Overvoltage Set Back Area Figure 20. IC Power Thermal Shutdown 180°C (typ) Voltage Quiescent Current Power Further reduction in power to the NCV7680 can be achieved by moving the VP pin connection to the drain of the external FET. The contribution of power at the NCV7680 caused by the quiescent current into VP is lowered due to the lower operating voltage of VP with the new connection. Note also the addition of an external resistor Rsd in Figure 21. This will be required to insure startup of the system. A value for Rsd should be chosen low enough to provide current into VP and the current in the ILEDs & feedback string under all required input voltage input conditions. Rsd’s value should be chosen lower for slow rising Vbat signals to avoid switching between an Output Disable state and an Open Circuit state during power−up. Input Voltage and Set Back Current Automotive battery systems have wide variations in line supply voltage. Low dropout is a key attribute for providing consistent LED light output at low line voltage. Unlike adjustable regulator based constant current source schemes where the set point resistor resides in the load path, the NCV7680’s set point resistor lies outside the LED load path, and aids in the low dropout capability. Setback Current Limit is employed during high voltage. During a Setback Current Limit event, the drive current is http://onsemi.com 12 NCV7680 Rsd Vbat MRA4003T3G C1 0.1 mF NTD2955 R3 1K ILEDs & feedback C2 0.22 mF C3 100 nF OUT1 NCV7680 OUT2 VP OUT3 Ballast Drive OUT4 GND FB STOP OUT5 DIAG OUT6 RSTOP OUT7 RTAIL OUT8 Figure 21. Alternative VP Connection with Rsd Programmability Alternatively, the equations below can be used to calculate a typical value and used for worst case analysis. Strings of LEDs are a common configuration for RCL applications. The NCV7680 provides eight matched outputs allowing individual string drive with current set by a single resistor. Individual string drive is a benefit to ensure equal current distribution amongst all of the strings. Output currents are mirrored and matched within ±5% at hot temperature. A high STOP condition sets the output current using equation 1 below. A low STOP condition, modulates the output currents at a duty cycle (DC) programmed using equation 2 below. Note, current limiting on RSTOP limits the current which can be referenced from the RSTOP Pin. Exceeding the RSTOP Current Limit will reduce the output current and the DIAG Pin will go high (reference Figure 18). This helps limit output current (brightness and power) for this type of fault. The average ISTOP Duty Cycle current provides the dimmed tail illumination function and assures a fixed brightness level for tail. The PWM generator’s fixed frequency (1 kHz typ.) oscillator allows flicker−free illumination. PWM control is the preferred method for dimming LEDs. The diagnostic function allows the detection of an open in any one of the output circuits. The active−low diagnostic output (DIAG) is coincident with the STOP input. DIAG remains high (pulled up) if an open load is detected in any LED string when STOP is high. Set the Stop Current using RSTOP OUTX + 100 R STOP_Bias_Voltage R STOP (eq. 1) RSTOP Bias Voltage = 1.08 V (typ) Set the Duty Cycle (DC) using RTAIL ǒ Ǔ 4 R TAIL + m R STOP(DC ) 0.1) (eq. 2) DC = duty cycle expressed in fractional form. (e.g. 0.50 is equivalent to 50% duty cycle) I m = 1.16 = Mirror Coupling Ratio = RTAIL I RSTOP (ground RTAIL when using external modulation) Output Current is directly tested per the electrical parameter table to be ±10% (with RSTOP = 3.09 kW) or 31.5 mA (min), 35 mA (typ), 38.5 mA (max) at room and hot temperature. Duty Cycle will vary according to the changes in RTAIL Voltage and RTAIL Bias Current (generated form the current through RSTOP). Voltage errors encompass generator errors (0.4 V to 4.4 V) and comparator errors and are included in testing as the Duty Cycle. Typical duty cycle measurements are 5% with RTAIL = 0.59 V and 70% with RTAIL = 3.29 V. RTAIL Bias Current errors are measured as RTAIL Bias Current and vary as 300 mA (min), 350 mA (typ), and 450 mA (max) with RSTOP = 3.09 kW. The error duality and choice of duty cycle levels make it difficult to specify duty cycle minimum and maximum limits, but worst case conditions can be calculated when considering the variation in the voltage threshold and current source. Duty Cycle variation must include the direct duty cycle as specified in the electrical parameter table plus an additional error due to the Irstop current which generates this voltage in the system. Output Current Programming Reference Figure 10 to choose programming resistor (RSTOP) value for stop current. Reference Figure 12 (Duty Cycle vs. RTAIL) to choose a typical value programming resistor for output duty cycle (with a typical RSTOP value of 3.09 kW). Note the duty cycle is dependent on both RSTOP and RTAIL values. RSTOP should always be chosen first as the stop current is only dependent on this value. http://onsemi.com 13 NCV7680 Using Equation 4 Choose a value for R7. R7 = 1k Vreg Oscillator and PWM Irstop R6 + − 4.4V 0.4V + The previously shown applications (Figures 4 and 5) show system operation using all 8 available channels of the NCV7680. When less than 8 channels are used, the unused OUTx pins can be grounded eliminating the unused OUTx drive current. This is accomplished by voltage threshold detection on OUTx (100 mV typ). A voltage less than 100 mV on OUTx turns the driver off, reducing quiescent current to the IC. This also helps reduce system power by eliminating the need for an external pullup resistor (from OUTx to VP) while maintaining open circuit detection. External pullup resistors may be used as an alternative. RTAIL Alternative Setup of Duty Cycle Alternatively, the duty cycle can be controlled by providing a voltage to the RTAIL pin as per Figure 13 (Duty Cycle vs. V(RTAIL). Note the pull-up current source (Irstop) is still present on the RTAIL pin due to current setting resistor connected to RSTOP. For proper operation the system designer needs to insure there is sufficient loading on the RTAIL pin such that Irstop does not pull the referenced voltage higher than its regulated state. Adding LED’s to the String The NCV7680 can function as a standalone device or in conjunction with additional support circuitry for more complex systems. Figure 23 shows the NCV7680 operating with a boost controller. This setup allows additional LEDs in a string to be increased. Eight are shown in the diagram. Consideration of the 45 V maximum limit on the OUTx Pin is the limitation of this configuration. The DC on voltage level on OUTx must also be considered for thermal reasons. Setting VSTRING VSTRING should be set to a level to allow proper operation of the IC without detecting an open circuit (0.5 V max on OUTx) and to keep power to the IC at reduced levels below the 150°C max die temperature thermal limit (die temperature will depend on printed circuit board composition, PCB size, thermal via number and placement, module component placement, and air flow). Example: VSTRING is set using resistors R6 and R7 (reference Figure 4). Electromagnetic Interference (EMI) One of the key contributors to electromagnetic interference is the rise and fall times of the electrical signals. This is a concern with both the initial startup of a device, and the repeated turn on/off cycles of a device. The NCV7680 employs current slew rate control. Each output is rated at 6.0 mA/ms (typ). Slew rate control reduces overshoot and allows for a predictable electrical signal. Slew rate control is used in the stop mode for soft−start and in the tail mode for low EMI operation. EMC susceptibility improvements to the NCV7680 device can be made by adding a ferrite bead directly on the VP (pin 2) of the device. The recommended component for this setup is the TDK PN/ MMZ2012S601A, FERRITE CHIP 600 OHM 500MA 0805 device. Care should be taken to add this component no less than 10mils from the pin. An R-C network can also be used as an alternative to the ferrite bead. A 100 W resistor in series with VP (pin 2) with a 1nF – 10 nF very low ESR ceramic capacitor provides a similar roll-off. A very-low ESR ceramic capacitor is a requirement here. A normal ceramic capacitor will not suffice in this setup. The design should consider that the dropout voltage of the LED strings must be higher than the minimum operating voltage of the IC plus the voltage drop across the 100 W resistor. (eq. 3) VFB = Ballast Drive Reference Voltage This simplifies to an equation for R6. R6 + R7ǒV STRING * V FBǓ V FB (eq. 4) Calculate system design VSTRING. Let VLED be the voltage drop across your LEDs (3 included in Figure 4). 9.5 V Choose a value for OUTx, 1 V V STRING + V OUTx ) V LED + 8.72k Reduced Channel Operation Figure 22. Duty Cycle Generator Circuitry ǒR6 ) 1Ǔ R7 1.08 V The closest standard resistor value is 8.87k. RTAIL V STRING + V FB 1kǒ10.5 V * 1.08 VǓ (eq. 5) Using Equation 3 V STRING + 1 V ) 9.5 V + 10.5 V http://onsemi.com 14 NCV7680 TAIL Input MRA4003T3G STOP Input MRA4003T3G C3 1mF + − + − R1 10k NCV3163 Boost Controller NCV7680 OUT2 OUT1 OUT3 VP Ballast Drive OUT4 R8, 10k FB GND STOP/PWM OUT5 R4, 3.09k C4 10nF R5, 2.21k Figure 23. Boost Mode http://onsemi.com 15 DIAG OUT6 RSTOP OUT7 RTAIL OUT8 epad NCV7680 Cross-Coupled LEDs VSTRING The setup in Figure 24 shows the LEDs set up in a cross-coupled configuration connected to all the outputs of the NCV7680 in parallel. This allows the user to maintain illumination of all the remaining LEDs when one fails due to an open circuit (the most common form of LED failure). Comparatively, the standard setup shown in Figure 4 will result in a full string turning off when one LED is open. Be aware as LEDs fail as open circuits in the cross-coupled arrangement will cause the row of LEDs to run at a higher current level affected by the smaller number of LEDs in that row. NCV7680 OUT1 OUT2 VP OUT3 Ballast Drive OUT4 FB GND STOP OUT5 DIAG OUT6 RSTOP OUT7 RTAIL OUT8 epad Figure 24. Cross Coupled LEDs http://onsemi.com 16 NCV7680 MRA4003T3G TAIL Input VSTRING NTD2955 MRA4003T3G STOP Input C3 100nF R3 1k C1 0.1mF C2 0.22mF R1 10k + − NCV7680 OUT2 OUT1 OUT3 VP Ballast Drive OUT4 FB GND STOP/PWM OUT5 R4, 3.09k C4 10nF DIAG OUT6 RSTOP OUT7 RTAIL OUT8 R5, 2.21k epad R6 8.87k Vref R7 1k LED Module Figure 25. No Tail Light, Stop Illuminated MRA4003T3G TAIL Input MRA4003T3G STOP Input C1 0.1mF VSTRING NTD2955 C3 100nF R3 1k C2 0.22mF R1 10k + − NCV7680 OUT2 OUT1 OUT3 VP Ballast Drive OUT4 FB GND STOP/PWM OUT5 R4, 3.09k C4 10nF DIAG OUT6 RSTOP OUT7 RTAIL OUT8 R5, 2.21k epad R6 8.87k Vref R7 1k LED Module Figure 26. Tail Light Illuminated, No Stop http://onsemi.com 17 NCV7680 VBAT or Boost Voltage MRA4003T3G 6V C3 1mF PWM C5 1mF R1 10k NCV7680 OUT2 OUT1 OUT3 VP Ballast Drive OUT4 FB GND STOP/PWM OUT5 R4, 3.09k C4* 10nF DIAG OUT6 RSTOP OUT7 RTAIL OUT8 epad * Optional for EMI considerations Figure 27. PWM Operation (suggested LCD backlighting applications) External PWM Operation Tail Frequency Stabilization Time requires 2 pulses from the internal oscillator. This is typically 2 ms (from the 1 kHz oscillator. Circuit limitations dictate the maximum output current (IOUTX) to be 60 mA when operated at VP = 5 V. Part capability increases up to the part maximum capability as VP is increased. Using the NCV7680 in a PWM setup requires RTAIL to be grounded. Grounding RTAIL disables the internal PWM circuitry. With RTAIL grounded, the STOP input pin can then be modulated externally with a microprocessor using the STOP logic input level thresholds. http://onsemi.com 18 NCV7680 Latch−Off on Open String Detection the DIAG pin coupled with external discrete transistors provides the feedback needed to the FB pin to turn off the ballast transistor drive removing the LED anode string from any power source. This condition is held until the input signal is toggled. Some LED lighting systems require the complete lighting system to shut down when the output intensity has diminished. This eliminates a slow degradation of output illumination. Figure 28 provides one solution for this requirement. The open circuit fault information provided on TAIL Input MRA4003T3G STOP Input MRA4003T3G VSTRING NTD2955G C1 0.1uF R3 C2 1k 0.22uF C3 100nF MRA4003T3G R1 10k NCV7680 R10 10k R11 10k R4, 3.09k R5, 2.21k R2 4.99k MUN2211 OUT2 VP OUT3 Ballast Drive OUT4 FB R9, 499 MUN2111LT1G C4 10nF OUT1 GND STOP OUT5 DIAG OUT6 RSTOP OUT7 RTAIL OUT8 R6 8.87K C6 0.1uF Vref R7 1K Note: Latch−off will be implemented under all conditions which cause DIAG to go high. Reference the pin function description table for a summary of DIAG performance. Figure 28. Latch−Off Circuit Checking DIAG After Assembly Using the electrical parameters in the datasheet, we have: (x% reduction)=20, kv=4%min(@20% reduction), VP(1% reduction)max=24.5V. Production requirements often require the functional testing of all parameters in a system. This can be a difficult parameter to check if the function is exercising the DIAG pin. You cannot easily create an open circuit condition to check on the reporting capability of the DIAG pin. This would require you to remove one or all LEDs in a string. As an alternative you can use the Set Back Current Limit function of the device. Increasing the voltage to the VP pin (STOP mode) will cause the current through the LEDs to decrease. Because DIAG also reports when the current limit has decreased 20%, we can calculate the minimum voltage needed to create that condition. The Voltage Fold-Back equation is: VP@(x% reduction) + ǒ Ǔ x% reduction kv VP(@20% reduction) max + ǒ204Ǔ V ) 24.5 V + 29.5 V (eq. 7) This is the maximum worst case voltage the NCV7680 will toggle the DIAG pin at VP. An additional increase in voltage should be used for good engineering judgment here. A supply voltage of 32V is recommended. Note the maximum capability of the VP and DIAG pins is 45V. An alternative to supplying the higher voltage on VP to toggle DIAG requires the short the Rstop pin to ground (must be less than 0.5 V). Note the Rstop pin is self-protected as per Figure 18 Iout vs. Irstop. (eq. 6) ) VP(1% reduction) Where kv= %/V http://onsemi.com 19 NCV7680 PACKAGE DIMENSIONS SOIC 16 LEAD WIDE BODY, EXPOSED PAD CASE 751AG−01 ISSUE A −U− A M P 0.25 (0.010) M W M 16 NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 2. CONTROLLING DIMENSION: MILLIMETER. 3. DIMENSION A AND B DO NOT INCLUDE MOLD PROTRUSION. 4. MAXIMUM MOLD PROTRUSION 0.15 (0.006) PER SIDE. 5. DIMENSION D DOES NOT INCLUDE DAMBAR PROTRUSION. ALLOWABLE PROTRUSION SHALL BE 0.13 (0.005) TOTAL IN EXCESS OF THE D DIMENSION AT MAXIMUM MATERIAL CONDITION. 6. 751R-01 OBSOLETE, NEW STANDARD 751R-02. 9 B 1 R x 45_ 8 −W− G PIN 1 I.D. 14 PL DETAIL E TOP SIDE C F −T− 0.10 (0.004) T K D 16 PL 0.25 (0.010) T U M SEATING PLANE W S J S DETAIL E H EXPOSED PAD 1 DIM A B C D F G H J K L M P R 8 INCHES MIN MAX 0.400 0.411 0.292 0.299 0.093 0.104 0.014 0.019 0.020 0.035 0.050 BSC 0.136 0.144 0.010 0.012 0.000 0.004 0.186 0.194 0_ 7_ 0.395 0.415 0.010 0.029 SOLDERING FOOTPRINT* L 16 MILLIMETERS MIN MAX 10.15 10.45 7.40 7.60 2.35 2.65 0.35 0.49 0.50 0.90 1.27 BSC 3.45 3.66 0.25 0.32 0.00 0.10 4.72 4.93 0_ 7_ 10.05 10.55 0.25 0.75 0.350 9 Exposed Pad 0.175 0.050 BACK SIDE CL 0.200 0.188 CL 0.376 0.074 0.150 0.024 DIMENSIONS: INCHES *For additional information on our Pb−Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D. ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC 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 special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. 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