NCL30100 Fixed Off Time Switched Mode LED Driver Controller The NCL30100 is a compact switching regulator controller intended for space constrained constant current high--brightness LED driver applications where efficiency and small size are important. The controller is based on a peak current, quasi fixed--off time control architecture optimized for continuous conduction mode step--down (buck) operation. This allows the output filter capacitor to be eliminated. In this configuration, a reverse buck topology is used to control a cost effective N--type MOSFET. Moreover, this controller employs negative current sensing thus minimizing power dissipation in the current sense resistor. The off time is user adjustable through the selection of a small external capacitor, thus allowing the design to be optimized for a given switching frequency range. The control loop is designed to operate up to 700 kHz allowing the designer the flexibility to use a very small inductor for space constrained applications. The device has been optimized to provide a flexible inductive step--down converter to drive one or more high power LED(s). The controller can also be used to implement non--isolated buck--boost driver topologies. http://onsemi.com MARKING DIAGRAM TSOP--6 (SOT23--6, SC59--6) XXXAYWG G SN SUFFIX CASE 318G 1 1 XXX A Y W G PIN CONNECTIONS Features TSOP--6 Quasi--Fixed OFF Time, Peak Current Control Method N--FET Based Controller Architecture Up to 700 kHz Switching Frequency Up to >95% Efficiency No Output Capacitor Needed VCC Operation from 6.35 -- 18 V Adjustable Current Limit with Negative Sensing Inherent Open LED Protected Very Low Current Consumption at Startup Undervoltage Lockout Compact Thin TSOP--6 Pb--Free Package --40 to + 125C Operating Temperature Range This is a Pb--Free Device CS 1 6 Gate GND 2 5 VCC CT 3 4 IVC (Top View) ORDERING INFORMATION Device NCL30100SNT1G Package Shipping† TSOP--6 (Pb--Free) 3000 / 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. Typical Applications = Specific Device Code =Assembly Location = Year = Work Week = Pb--Free Package Low Voltage Halogen LED Replacement (MR--16) LED Track Lighting Landscape Lighting Solar LED Applications Transportation Lighting 12 V LED Bulb Replacement Outdoor Area Lighting LED Light Bars Semiconductor Components Industries, LLC, 2010 June, 2010 -- Rev. 0 1 Publication Order Number: NCL30100/D NCL30100 6.5 – 24 V + C1 R1 LED2 R2 LED1 IC1 NCL30100 R3 CS -- D1 LEDX DRV L1 GND VCC CT IVC C2 D2 C3 Q1 R4 Figure 1. Typical Application Example of the LED Converter PIN FUNCTION DESCRIPTION Pin N Pin Name Function Pin Description 1 CS Current sense input 2 GND Ground 3 CT Timing capacitor 4 IVC Input voltage compensation 5 VCC Input supply Supply input for the controller. The input is rated to 18 V but as illustrated Figure 1, a simple zener diode and resistor can allow the LED string to be powered from a higher voltage 6 DRV Driver output Output drive for an external power MOSFET A resistor divider consisting of R3 and R4 is used to set the peak current sensed through the MOSFET switch Power ground. Capacitor to establish the off time duration The current injected into the input varies the switch off time and IPK allowing for feedforward compensation. http://onsemi.com 2 NCL30100 IVC Input Voltage Regulator VOffset VDD Reference Regulator Iref Undervoltage Lockout VCC 6.35/5.85 V OFF Time Comparator 0--3.9 V CT 50 mA CS Gate Driver Set 12.5--50 mA S Q R Q DRV SET CLR Reset GND Current Sense Comparator Figure 2. Simplified Circuit Architecture MAXIMUM RATINGS Rating Symbol Value Unit Power Supply Voltage VCC 18 V IVC Pins Voltage Range IVC --0.3 to 18 V CS and CT Pin Voltage Range Vin --0.3 to 10 V RθJA 178 C/W Thermal Resistance, Junction--to--Air Junction Temperature TJ 150 C Storage Temperature Range Tstg --60 to +150 C ESD Voltage Protection, Human Body Model (HBM) VESD--HBM 2 kV ESD Voltage Protection, Machine Model (MM) VESD--MM 200 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. This device(s) contains ESD protection and exceeds the following tests: Human Body Model 2000 V per JEDEC Standard JESD22--A114E Machine Model 200 V per JEDEC Standard JESD22--A115--A 2. This device meets latchup tests defined by JEDEC Standard JESD78. 3. Moisture Sensitivity Level (MSL) 1. http://onsemi.com 3 NCL30100 ELECTRICAL CHARACTERISTICS (VCC = 12 V, for typical values TJ = 25C, for min/max values TJ = --40C to +125C, unless otherwise noted) SUPPLY SECTION Parameter Conditions Symbol Min Typ Max Unit V(offset) 1.10 1.30 1.45 V 2.08 2.47 V 2.6 3.05 V INPUT VOLTAGE COMPENSATION Offset Voltage CT Pin Voltage IVC Current = 25 mA (Including V(offset)) VCT--25mΑ 1.69 CT Pin Voltage IVC Current = 50 mA (Including V(offset)) VCT--50mA 2.12 IVC pin internal resistance (Note 4) RIVC 17 kΩ CT PIN – OFF TIME CONTROL Source Current CT Pin Grounded, 0 ≤ TJ ≤ 85C ICT 47.25 50 52.75 mA Source Current CT Pin Grounded, --40 ≤ TJ ≤ 125C ICT 45.25 50 52.75 mA VCT(max) -- 4.3 -- V VCT(min) -- -- 20 mV CCT -- 8 -- pF CT Reach VCT Threshold to Gate Output CTdelay -- 220 -- ns Minimum Source Current IVC = 180 mA, CT Pin Grounded, 0 ≤ TJ ≤ 85C ICS(min) 11. 75 12.5 13.25 mA Minimum Source Current IVC = 180 mA, CT Pin Grounded, --40 ≤ TJ ≤ 125C ICS(min) 11.35 12.5 13.25 mA Maximum Source Current IVC = 0 mA, CT Pin Grounded, 0 ≤ TJ ≤ 85C ICS(max) 47.25 50 52.75 mA Maximum Source Current IVC = 0 mA, CT Pin Grounded, --40 ≤ TJ ≤ 125C ICS(max) 45.25 50 52.75 mA Vth -- 38 -- mV CS Falling Edge to Gate Output CSdelay -- 215 310 ns Isink = 30 mA ROL 5 15 40 Ω Isource = 30 mA ROH 20 60 100 Ω Startup Threshold VCC increasing VCC(on) -- 6.35 6.65 V Minimum Operating Voltage VCC decreasing VCC(off) 5.45 5.85 -- V VCC(hyst) -- 0.5 -- V VCC = 6 V ICC1 -- 22 35 mA Steady State Current Consumption (Note 4) CDRV = 0 nF, fSW = 100 kHz, IVC = open, VCC = 7 V ICC1 Steady State Current Consumption CDRV = 1 nF, fSW = 100 kHz, IVC = open, VCC = 7 V ICC2 Source Current Maximum Voltage Capability (Note 4) Minimum CT Pin Voltage (Note 4) Pin Unloaded, Discharge Switch Turned on Pin to ground capacitance (Note 4) Propagation Delay (Note 4) CURRENT SENSE Comparator Threshold Voltage (Note 4) Propagation Delay GATE DRIVER Sink Resistance Source Resistance POWER SUPPLY Vcc Hysteresis (Note 4) Startup Current Consumption 4. Guaranteed by design http://onsemi.com 4 300 0.5 1 mA 1.15 mA NCL30100 6.260 30 28 26 6.255 6.250 ICC1 (mA) VCC(on) (V) 24 6.245 22 20 18 16 14 6.240 12 6.235 --40 --20 0 20 40 60 80 100 10 120 --20 0 20 40 60 80 100 120 TEMPERATURE (C) Figure 3. Vstartup Threshold vs. Junction Temperature Figure 4. Startup Current Consumption vs. Junction Temperature 12.6 5.780 12.5 5.775 12.4 5.770 12.3 12.2 VCC(off) (V) ICS(min) (mA) --40 TEMPERATURE (C) 12.1 12.0 11.9 5.765 5.760 5.755 5.750 11.8 5.745 11.7 11.6 --40 --20 0 20 40 60 80 TEMPERATURE (C) 100 5.740 120 --40 Figure 5. Minimum Source Current vs. Junction Temperature --20 0 20 40 60 80 TEMPERATURE (C) 100 120 Figure 6. Minimum Operating Voltage Threshold vs. Junction temperature 50.0 1.10 49.5 ICS(max) (mA) ICC2 (mA) 1.05 1.00 49.0 48.5 48.0 0.95 47.5 0.90 --40 --20 0 20 40 60 80 TEMPERATURE (C) 100 47.0 --40 120 Figure 7. Steady State Current Consumption vs. Junction Temperature --20 0 20 40 60 80 TEMPERATURE (C) 100 Figure 8. Maximum Source Current vs. Junction Temperature http://onsemi.com 5 120 55 1.350 50 1.345 45 1.340 V(offset) (V) Vth (mV) NCL30100 40 35 30 1.335 1.330 1.325 25 --40 --20 0 20 40 60 80 100 1.320 --40 120 20 40 60 80 100 TEMPERATURE (C) Figure 9. Comparator Threshold Voltage vs. Junction Temperature Figure 10. Offset Voltage vs. Junction Temperature 85 51.0 75 50.5 120 50.0 ROH 55 49.5 ICT (mA) RESISTANCE (Ω) 0 TEMPERATURE (C) 65 45 35 49.0 48.5 48.0 25 ROL 15 5 --40 --20 0 20 47.5 40 60 80 100 47.0 --40 120 --20 0 20 40 60 80 100 TEMPERATURE (C) TEMPERATURE (C) Figure 11. Drive Sink and Source Resistance vs. Junction Temperature Figure 12. CT Source Current vs. Junction Temperature 2.60 120 50 45 2.55 40 2.50 CURRENT (mA) VCT--50mA (V) --20 2.45 2.40 35 30 25 20 15 10 2.35 5 2.30 --40 0 --20 0 20 40 60 80 100 0 120 20 40 60 80 100 120 140 160 180 200 TEMPERATURE (C) CURRENT (mA) Figure 13. CT Pin Voltage vs. Input Voltage Compensation Current Figure 14. IVC on ICT Dependence http://onsemi.com 6 NCL30100 APPLICATION INFORMATION The NCL30100 implements a peak current mode control scheme with a quasi--fixed OFF time. An optional input feedforward voltage control is provided to enhance regulation response with widely varying input voltages. Only a few external components are necessary to implement the buck converter. The NCL30100 incorporates the following features: Very Low Startup Current: The patented internal supply block is specially designed to offer a very low current consumption during startup. Negative Current Sensing: By sensing the total current, this technique does not impact the MOSFET driving voltage (VGS) during switching. Furthermore, the programming resistor together with the pin capacitance forms a residual noise filter which blanks spurious spikes. This approach also supports a flexible resistor selection. Finally unlike a positive sensing approach, there is virtually no power dissipation in the current sense resistor thus improving efficiency. Controller architecture supports high brightness LED drive current requirements: Selection of the external n--channel MOSFET can be easily optimized based on operation voltage, drive current and size giving the designer flexibility to easily make design tradeoffs. Typical ±5.5% Current Regulation: The ICS pin offers ±5.5% from 0 to 85C (+5.5% --9.5% across --40C to 125C) accuracy of the current typically, so the LED peak current is precisely controlled No output capacitor is needed: By operating the controller in continuous conduction mode, it is possible to eliminate the bulky output filter capacitor. the switch and the inductor. This approach offers several benefits over traditional positive current sensing. Maximum peak voltage across the current sense resistor is user controlled and can be optimized by changing the value of the shift resistor. The gate drive capability is improved because the current sense resistor is located out of the gate driver loop and does not deteriorate the switch on and also switch off gate drive amplitude. Natural leading edge blanking is filter switching noise at FET turn--in The CS pin is not exposed to negative voltage, which could induce a parasitic substrate current within the IC and distort the surrounding internal circuitry. The current sensing circuit is shown in Figure 15. IVC Input Voltage Regulator 12.5--50 mA CS To Latch Vshift Rshift RCS The following section describes in detail each of the control blocks GND Iprimary VCS Current Sensing Block Figure 15. Primary Current Sensing The NCL30100 utilizes a technique called negative current sensing which is used to set the peak current through http://onsemi.com 7 NCL30100 From Input Voltage Compensation Block Once the external MOSFET is switched on, the inductor current starts to flow through the sense resistor RCS. The current creates a voltage drop VCS on the resistor RCS, which is negative with respect to GND. Since the comparator connected to CS pin requires a positive voltage, a voltage Vshift is developed across the resistor Rshift by a current source which level--shifts the negative voltage VCS. The level--shift current is in the range from 12.5 to 50 mA depending on the optional input voltage compensation loop control block signal (see more details in the input voltage compensation section). The peak inductor current is equal to: I pk = I CS ⋅ R shift − V th VOffset VOffset to VDD CT CT 50 mA To Latch’s Output (eq. 1) R CS To achieve the best Ipk precision, higher values of ICS should be used. The Equation 1 shows the higher drop on RCS reduces the influence of the Vth tolerance. Vth is the comparator threshold which is nominally 38 mV. A typical CS pin voltage waveform for continuous condition mode is shown in Figure 16. V To Latch’s Set Input GND Figure 17. OFF Time Control During the switch--on time, the CT capacitor is kept discharged by an internal switch. As soon as the latch output changes to a low state, the Isource is enabled and the voltage across CT starts to ramp--up until its value reaches the threshold given by the Voffset. The current injected into IVC can change this threshold. The IVC operation will be discussed in the next section. Ishift = 50 mA V Ishift = 12.5 mA VDD Switch Turn on IVC Goes Up CT pin Voltage 0 t IVC Goes Down Voffset Figure 16. CS Pin Voltage I1 I2 I3 0 Figure 16 also shows the effect of the inductor current based on the range of control possible via the IVC input. toff--min t Figure 18. CT Pin Voltage OFF Time Control The voltage that can be observed on CT pin is shown in Figure 18. The bold line shows the minimum IVC current when the off time is at its minimum. The amount of current injected into the IVC input can increase the off time by changing the turn off comparator switching threshold. I1, I2, The internal current source, together with an external capacitor, controls the switch--off time. In addition, the optional IVC control signal can modulate the off time based on input line voltage conditions. This block is illustrated in Figure 17. http://onsemi.com 8 NCL30100 VCC and I3 represent different delays depending on the magnitude of IVC. Current Mirror 1:1 Gate Driver The Gate Driver consists of a CMOS buffer designed to directly drive a power MOSFET. It features unbalanced source and sink capabilities to optimize switch on and off performance without additional external components. The power MOSFET is switched off at high drain current, to minimize its switch off losses the sink capability of the gate driver is increased for a faster switch off. On the other hand, the source capability of the driver is reduced to slow--down the power MOSFET at switch on in order to reduce EMI generation. Whenever the IC supply voltage is lower than the under voltage threshold, the Gate Driver is low, pulling down the gate to ground thus eliminating the need for an external resistor. VOffset 17 kΩ IVC Current Mirror 1:1 To OFF Time Comparator 45 kΩ Figure 19. Input Voltage Compensation, OFF Time Control Input Voltage Compensation: OFF Time Comparator Input Voltage The Input Voltage Compensation block gives the user optional flexibility to sense the input voltage and modify the current sense threshold and off time. This function provides a feed forward mechanism that can be used when the input voltage of the controller is loosely regulated to improve output current regulation. If the input voltage is well regulated, the IVC input can also be used to adjust the offset of the off time comparator and the current sense control to achieve the best current regulation accuracy. An external resistor connected between IVC and the input supply results in a current being injected into this pin which has an internal 17 kΩ resistor connected to a current mirror. This current information is used to modify Voffset and ICS. By changing Voffset the off time comparator threshold is modified and the off time is increased. A small capacitor should be connected between the IVC pin and ground to filter out noise generated during switching period. Figure 19 shows the simplified internal schematic: V VDD Voffset 0 IVC Pin Sink Current mA Figure 20. IVC Loop Transfer Characteristic The transfer characteristic (output voltage to input current) of the input voltage compensation loop control block can be seen in Figure 20. VDD refers to the internal stabilized supply. If no IVC current is injected, the off time comparator is set to Voffset. The value of the current injected into IVC also change Ics. This is accomplished by changing the voltage drop on Rshift. The corresponding block diagram of the IVC pin can be seen in Figure 21. To Current Sense Comparator 17 kΩ CS IVC Current Mirror 4:3 37.5 mA 12.5 mA Figure 21. Input Voltage Compensation Loop – Current Sense Control http://onsemi.com 9 NCL30100 The current sense characteristic can be seen in Figure 22. As illustrated, by varied the IVC current between 0 -- 50 mA, the sourcing current can range from 12.5 to 50 mA. V CS Pin Source Current 50 mA 12.5 mA 0 mA 50 mA 100 mA mA 140 mA IVC Pin Sink Current Figure 22. Current Sense Regulation Characteristic Biasing the controller t on = L ⋅ The NCL30010 Vcc input can range up to 18 V. For applications that have an input voltage that is greater than that level, an external resistor should be connected between Vin and the VCC supply capacitor. The value of the resistor can be calculated as follows: R2 = V in − V CC I CC2 V in + CS delay (eq. 4) Where: L -- Inductor inductance Ipk -- Peak current As seen from the above equation, the turn on time depends on the input voltage. In the case of a low voltage AC input where there is ripple due to the time varying input voltage and input rectifier, natural frequency dithering is produced to improve the EMI signature of the LED driver. The turn off time is determined by the charging of the external capacitor connected to the CT pin. The minimum toff value can be computed as: (eq. 2) Where: VCC -- Voltage at which IC operates (see spec.) ICC2 – Current at steady state operation Vin -- Input voltage The ICC current is composed of two components: The quiescent current consumption (300 mA) and the switching current consumption. The driver consumption depends on the MOSFET selected and the switching frequency. Total current consumption can be calculated using following formula: I CC = 300 ⋅ 10 --6 + C MOSFET ⋅ V CC ⋅ f switching I pk t off = C T ⋅ V offset I CT + CT delay (eq. 5) Where: Voffset -- Offset voltage (see parametric table) ICT -- CT pin source current (see parametric table) Finally, the switching frequency then can be evaluated by: (eq. 3) In applications where the input voltage Vin is varying dramatically, a zener can be used to limit the voltage going into VCC, thus reducing the switching current contribution. F SW = 1 = L⋅I t on + t off pk V Switching Frequency in 1 + (eq. 6) C ⋅V T offset + 435 ⋅ 10 --9 50⋅10 --6 The sum of the nominal CSdelay and CTdelay is approximately 435 nsec. The switching frequency varies with the output load and input voltage. The highest frequency appears at highest input voltage. Since the peak inductor current is fixed, the on--time portion of the switching period can be calculated: http://onsemi.com 10 NCL30100 Reverse Buck Operating Description Figure 23 illustrates a typical application schematic and Figure 24 displays simplified waveforms illustrate the converter in steady state operation for critical circuit nodes. Imag D1 Vin ICS Rshift ICT Idemag IC1 NCL30100 1 CS 2 GND 3 CT 6 DRV VCC 5 L1 Q1 4 IVC VCS Vsense CT VCT VDRV Rsense Figure 23. Simplified Application Schematic http://onsemi.com 11 LED NCL30100 Vcc VDRV 0 Ipk Imag 0 Idemag Imin 0 I LED 0 50 uA ICT 0 VCT 0 0 V Sense I CS 0 VCS 38 mV 0 Figure 24. Voltage and Current Nodes in the Application Circuit approaching zero. On the CS pin there is a comparator with a reference level of 38 mV. Once the voltage on the CS pin reaches this reference level, the DRV output is turned off and current path Imag disappears. Energy stored in the inductor as a magnetic field keeps current flowing in the same direction. The current path is now closed via diode D1 (green line). Once the DRV is turned off, the internal current source starts to charge the CT capacitor and the voltage on this node increases. Once the CT capacitor voltage reaches the VCT level, Q1 is turned on and an internal switch discharges the CT capacitor to be ready for the next switching cycle. The current follows the red line in Figure 23 when Q1 is turned on. The converter operates in continuous conduction mode therefore the current through the inductor never goes to zero. When the switch is on, the current creates a negative voltage drop on the Rsense resistor. This negative voltage can not be measured directly by the IC so an Rshift resistor is connected to CS pin. Inside the IC there is a current source connected to this pin. This current source creates constant voltage drop on resistor Rsense which shifts the negative voltage drop presented on Rsense positive. The magnetizing current Imag increases linearly, the negative voltage on Rsense increased as well. Thus the voltage on CS pin http://onsemi.com 12 NCL30100 Application Design Example: A typical step down application will be used to illustrate the basic design process based on nominal design parameters: Input voltage: Vin -- 12 Vac (12 V dc after the bridge) Nominal LED current: 700 mA (rms) LEDripple: 120 mA (peak--to--peak) VLED: 3.2 V Freewheel diode Vf: 0.5 V Target Switching Frequency: 450 kHz Dimming using PWM signal 1 kHz with duty cycle 0 – 99% 12 V Vac A D4 R2 D5 Vac D3 NCL30100 IC1 R3 D7 D1 R1 C1 D6 CS R5 L3 DRV K Q1 GND VCC CT IVC C2 Q2 D2 C5 C3 R4 R9 DIMM 0/5 V R8 Figure 25. Example Design Schematic Note this simplified step--by--step design process neglects any parasitic contribution of the PCB. First, we need to determine the nominal tON/tOFF ratio: V LED + V f 3.2 + 0.5 3.7 t on = = = t off 12 − 3.2 8.8 V in − V LED Now all the parameters are defined to calculate inductor value: V= di ⋅ L (eq. 7) = Next the typical duty cycle (DC) will be calculated: DC = t ON t ON + t OFF = 3.7 = 0.296 3.7 + 8.8 1 f op = 1 450 ⋅ 10 3 = 2.222 ms V IN − V LED ⋅ t ON I ripple (12 − 3.2) ⋅ 658 ⋅ 10 --9 0.12 (eq. 11) ≅ 48.3 mH A standard value 47 mH is chosen. Next the CT capacitor can be calculated, but we need to first determine the IVC current which can be simply calculated. (eq. 8) Target switching frequency is set at 450 kHz, now we need to determine the period: T= dt ⇒L= I IVC = (eq. 9) V 12 = ≅ 7.91 mA 6 R + R IVC 1.5 ⋅ 10 + 17 ⋅ 10 3 (eq. 12) The IVC current controls the dependence of the peak current to the input voltage. If the input voltage is well regulated, the IVC pin should be grounded. The value for IVC resistor should be chosen based on graphs below. Note as well that the IVC can be used to implement analog dimming since increasing the current into IVC pin will decrease the Ipeak of the LED). Combination the previous equation we can calculate the tON and tOFF durations: t ON = DC ⋅ T = 0.296 ⋅ 2.222 ⋅ 10 --6 = 658 ns (eq. 10) t OFF = (1 − DC) ⋅ T = (1 − 0.296) ⋅ 2.222 ⋅ 10 --6 = 1.564 ms http://onsemi.com 13 NCL30100 600 1000 900 500 800 400 ILED (mA) ILED (mA) 700 600 Rivc = 300k 500 Rivc = 510k 400 Rivc = 1 Meg Rivc = 300k 200 Rivc = 1 Meg Rivc = 510k Rivc = 1.5 Meg 300 Rivc = 1.5 Meg Rivc = 2.2 Meg Rivc = infinity 7 8 9 10 Rivc = 2.2 Meg 100 Rivc = 3.7 Meg 200 100 300 11 12 13 14 15 INPUT VOLTAGE (V) 16 17 0 18 Rivc = 3.7 Meg Rivc = infinity 7 Figure 26. Rivc Impact versus Vin for ILED = 700 mA Nominal --0.26 ⋅ IVC 2 + 45.5 ⋅ IVC + 1625 [V] (eq. 13) 1250 2 --0.26 ⋅ 7.91 ⋅ 10 --6 + 45.5 ⋅ 7.91 ⋅ 10 --6 + 1625 (eq. 14) = dv ⋅ C dt ⇒ C CT = I CS = --0.75 ⋅ IVC + 50 ⋅ 10 --6 50 ⋅ 10 --6 ⋅ 1.654 ⋅ 10 --6 − 220 ⋅ 10 --9 1.3 17 18 (eq. 16) (eq. 17) = --0.75 ⋅ 7.91 ⋅ 10 --6 + 50 ⋅ 10 --6 ≅ 44.07 mA I CT ⋅ t OFF − CT delay V CT 16 Therefore: The CT capacitance can be calculated using the equations above: I= 11 12 13 14 15 INPUT VOLTAGE (V) I CS = --0.75 ⋅ IVC + 50 ⋅ 10 --6 [mA] 1250 ≅ 1.3 V 10 subtracted from the calculated value in Equation 15. The calculated value is not standard, so the nearest value 33 pF has been selected. Now we can calculate the IPK of LED. The average value is set to 700 mA and the target ripple is set at 120 mA, the IPK equals 760 mA. Rshift has been chosen to be as small a voltage drop as possible to minimize power dissipation so an Rshift of 100 mΩ has been selected. Before calculation of Rshift we need to know the ICS current, which affects the offset on Rshift. The ICS value dependents on the IVC current and for IVC currents between 0 -- 50 mA, it can be described by this formula: Using the result from Equation 12 and put it to Equation 13 the VCT threshold will be calculated: V CT = 9 Figure 27. Rivc Impact versus Vin for ILED = 350 mA Nominal A value 1.5 MΩ was used since the input voltage has a sinusoidal component due to the low voltage AC input and desires to have a small bulk capacitance, thus compensating for part of this variation. The dependence of VCT on IVC current is described by the following equation: V CT = 8 To calculate Rshift it is necessary to know the Ipk current through the inductor. From the time that the current sense comparator detects that the peak current threshold has been crossed to the time that the external MOSFET switch is turned off there is a propagation delay. Depending on the value of the inductor selected (which is based on the target switching frequency), there is a current error between the intended peak current and the actual peak current, this is illustrated in Figure 28. (eq. 15) ≅ 55.1 pF The intrinsic pin capacitance CT pin (~8 pF) in conjunction with the dimming transistor (~10 pF) in this schematic approximately 18 pF so this value must be http://onsemi.com 14 NCL30100 Ipeak Ics ILED ΔiL td (Vin-VLED) -VLED - Vdiode L L ton toff Figure 28. A Current Error Between the Intended Peak Current and the Actual Peak Current V= di ⋅ L dt ⇒ I delay = V⋅t L = Using the PDIE, we can calculate junction temperature: 8.8 ⋅ 215 ⋅ 10 --9 47 ⋅ 10 --6 (eq. 18) Temp IC = T A + P DIE ⋅ R θJA = T A + 0.0399 ⋅ 178 ≅ 0.0402 A = T A + 7.1° C V/L is simply the slew rate through the inductor and td is the internal propagation delay so the current overshoot from target is approximately 40 mA as calculated in Equation 18. All values necessary for Rshift calculation are known, the Rshift value is described by this formula: R shift = = A design spreadsheet to aid in calculating the external components necessary for a specific set of operating conditions is available for download at the ON Semiconductor website. For a low voltage AC input diode D3 is placed into the Vcc line. Since Capacitor C3 is charged from a sinusoidal voltage. If the input voltage approaches zero, the IC is still supplied from C3. Due to this diode, the IC keeps the LED driver operating even if the sinusoidal voltage is lower than VCC(min) until Vin is lower than VLED. The use of this diode make sense only if a single LED is used and the converter is supplied by sinusoidal voltage 12 Vac. For two LEDs in series their forward voltage is almost as high as VCC(min) of the IC. Parasitic capacitance and inductance are presented in real applications which will have an influence on the circuit operation. They are depending on the PCB design which is user dependent. The BOM, PCB and some plots are enclosed for better understanding of the system behavior. R sense ⋅ I pk − I delay + V th I CS 0.1 ⋅ (0.76 − 0.0402) + 0.038 44.07 ⋅ 10 --6 (eq. 19) ≅ 2496 Ω This value of resistance can be a parallel combination of 2.7 kΩ and 30 kΩ. To understand the operating junction temperature, we calculate the die power dissipation: P DIE = V CC ⋅ 300 ⋅ 10 --6 + C MOSFET ⋅ V CC ⋅ f switching = 12 ⋅ 300 ⋅ 10 --6 + 560 ⋅ 10 --12 ⋅ 12 ⋅ 450 ⋅ 10 3 = 39.8 mW (eq. 21) (eq. 20) http://onsemi.com 15 NCL30100 Figure 29. PCB Design the Circuit Calculated Above. Only Single Layer PCB is Used for the Application. Figure 30. The Component Side (Several Transistor Packages are Possible to Use) BILL OF MATERIALS FOR THE NCL30100 Designator Qty Description Value Tol Footprint Manufacturer Manufacturer Part Number Substitution Allowed Pb--Free C1 1 Capacitor 2.2 mF / 25 V 10% 0805 AVX 08053C225KAT2A Yes Yes C2 1 Capacitor 33 pF 5% 0603 Kemet C0603C330J5GACTU Yes Yes C3 1 Capacitor 4.7 mF / 25 V 10% 0805 AVX 08053D475KAT2A Yes Yes C5 1 Capacitor 1 nF 10% 0603 Kemet C0603C104K5RACTU Yes Yes D1 1 Surface Mount Schottky Power Rectifier MBR130T3G -- SOD--123 ON Semiconductor MBR130T3G No Yes D2 1 Zener Diode 16 V 5% SOD--523 ON semiconductors MM5Z16VT1G No Yes D3 1 Schottky Diode NSR0520V2T1G -- SOD--523 ON semiconductors NSR0520V2T1G No Yes D4, D5, D6, D7 4 Schottky Diode NSR0340HT1G -- SOD--323 ON semiconductors NSR0340HT1G No Yes IC1 1 LED Driver NCL30100 -- TSOP--6 ON semiconductors NCL30100SNT1G No Yes L3 1 Inductors 47 mH 10% WE--PD2_M Wurth Electronik 744774147 No Yes Q1 1 Power MOSFET NTGS4141NT1G -- TSOP--6 ON semiconductors NTGS4141NT1G No Yes Q2 1 Power MOSFET NU -- SOT--223 ON semiconductors NTF3055--100T1G No Yes Option Q2 1 Power MOSFET NU -- DPAK ON semiconductors NTD23N03RT4G No Yes Option Q2 1 Power MOSFET NU -- SOT--363 ON semiconductors NTJS4160NT1G No Yes Option Q2 1 Power MOSFET NU -- SOT--23 ON semiconductors NTR4170NT1G No Yes Option Q3 1 General Purpose Transistor NPN BC817--16 -- SOT--23 ON semiconductors BC817--16LT1G No Yes http://onsemi.com 16 Comments NCL30100 BILL OF MATERIALS FOR THE NCL30100 Designator Qty Q3 1 R1 Description Value Tol Footprint Manufacturer Manufacturer Part Number Substitution Allowed Pb--Free Comments Power MOSFET NU -- SOT--23 ON semiconductors NTS4001NT1G No Yes Option 1 Resistor 1.5 M 1% 0603 Rohm Semiconductor MCR03EZPFX1504 Yes Yes R2 1 Resistor 300 R 1% 0603 Rohm Semiconductor MCR03EZPFX3000 Yes Yes R3 1 Resistor 30 k 1% 0603 Rohm Semiconductor MCR03EZPFX3002 Yes Yes R4 1 Resistor 0.1 R 1% 0805 Welwyn LRCS0805--0R1FT5 Yes Yes R5 1 Resistor 2.7 k 1% 0603 Rohm Semiconductor MCR03EZPFX2701 Yes Yes R8 1 Resistor 10 k 1% 0603 Rohm Semiconductor MCR03EZPFX1002 Yes Yes R9 1 Resistor 5.6 k 1% 0603 Rohm Semiconductor MCR03EZPFX5601 Yes Yes Figure 31. Completed PCB with Devices Figure 32. Snapshot of CT Pin Voltage, Driver and ILED Figure 33. Voltage Measured on RCS (R4) http://onsemi.com 17 NCL30100 Figure 34. Current Through LED if 50% Dimming at 1 kHz is Applied Figure 35. The Dimming Detail at 95%. No Overshoot in LED Current is Observed Figures 36 and 37 illustrate leading edge and trailing edge waveforms from a chopped AC source. For proper dimming control, the bulk capacitance must be reduced to a relatively small value to achieve best dimming range. Performance in real world application is dependent on the characteristics of the actual dimmer and the electronic transformer used to generated to chopped AC waveform Figure 36. Trailing Edge Dimming Figure 37. Leading Edge (Triac) Regulation. Small Overshoot is Seen on the Leading Edge, this is Based on the Abrupt Chopping of the Low Voltage AC Waveform http://onsemi.com 18 NCL30100 Figure 38. ILED and Vin Waveform if No Dimming is Used 84 83 680 82 CURRENT (mA) EFFICIENCY (%) 690 DC Voltage Efficiency (No Bridge Rectifier) 81 80 79 670 660 650 640 78 630 77 7 620 8 9 10 11 12 13 INPUT VOLTAGE (V) 14 15 16 LED Current Variation 7 Figure 39. Efficiency Measurement for the Demoboard (Vf = 3.2 Nominal) 8 9 10 11 12 13 INPUT VOLTAGE (V) 14 15 16 Figure 40. ILED Current Dependence on Input DC Voltage (No Bridge Rectifier is Used) Figure 39 represents the efficiency of the converter driving a single LED at a nominal current of 690 mA. The addition of the AC bridge rectifier contributes addition losses into the circuit and it is recommended to us low forward voltage schottky rectifiers to minimize power dissipation in the AC rectification stage. A specific two sided demo board was designed to fit with the MR--16 form factor. The schematic is almost the same for both, but the PWM dimming control circuitry has been removed. If the same components are used, the operation frequency will be slightly higher due to the lower pin capacitance because the dimming transistor contribution is removed. http://onsemi.com 19 NCL30100 12 V X2 A D3 D7 D4 D1 R1 C1 D5 X3 D6 R2 R3 NCL30100 R5 GND VCC CS CT DRV L1 Q1 K IVC C2 C4 C3 D2 R4 Figure 41. Schematic MR 16 Application Figure 42. PCB Top Side MR 16 Application Figure 43. PCB Top Side Devices Placement Figure 44. PCB Bottom Side MR 16 Application http://onsemi.com 20 NCL30100 Figure 45. PCB Bottom Side Devices Placement Figure 46. Top Side Photo Figure 47. Bottom Side Photo http://onsemi.com 21 NCL30100 BILL OF MATERIALS FOR THE NCL30100 MR 16 APPLICATION Designator Qty Description Value Tol Footprint Manufacturer Manufacturer Part Number Substitution Allowed Pb--Free Comments C1 1 Capacitor 2.2 mF / 25 V 10% 0805 AVX 08053C225KAT2A Yes Yes C2 1 Capacitor 33 pF 5% 0603 Kemet C0603C330J5GACTU Yes Yes C3 1 Capacitor 4.7 mF / 25 V 10% 0805 AVX 08053D475KAT2A Yes Yes C4 1 Capacitor 1 nF 10% 0603 Kemet C0603C104K5RACTU Yes Yes D1 1 Surface Mount Schottky Power Rectifier MBR130T3G -- SOD--123 ON Semiconductor MBR130T3G No Yes D2 1 Zener Diode 16 V 5% SOD--523 ON Semiconductor MM5Z16VT1G No Yes D3, D4, D5, D6 4 Schottky Diode NSR0340HT1G -- SOD--323 ON Semiconductor NSR0340HT1G No Yes D7 1 Schottky Diode NSR0520V2T1G -- SOD--523 ON Semiconductor NSR0520V2T1G No Yes IC1 1 LED Driver NCL30100 -- TSOP--6 ON Semiconductor NCL30100SNT1G No Yes L1 1 Inductors 47 mH 10% WE--PD2_M Wurth Electronik 744774147 No Yes Q1 1 Power MOSFET NTGS4141NT1G -- TSOP--6 ON Semiconductor NTGS4141NT1G No Yes Q1 1 Power MOSFET NU -- SOT--223 ON Semiconductor NTF3055--100T1G No Yes Option Q1 1 Power MOSFET NU -- SOT--363 ON Semiconductor NTJS4160NT1G No Yes Option Q1 1 Power MOSFET NU -- SOT--23 ON Semiconductor NTR4170NT1G No Yes Option R1 1 Resistor 1.5 M 1% 0603 Rohm Semiconductor MCR03EZPFX1504 Yes Yes R2 1 Resistor 300 R 1% 0603 Rohm Semiconductor MCR03EZPFX3000 Yes Yes R3 1 Resistor 30 k 1% 0603 Rohm Semiconductor MCR03EZPFX3002 Yes Yes R4 1 Resistor 0.1 R 1% 0805 Welwyn LRCS0805--0R1FT5 Yes Yes R5 1 Resistor 2.7 k 1% 0603 Rohm Semiconductor MCR03EZPFX2701 Yes Yes Application Design Example for an Offline (115 Vac) Buck Application: In addition to traditional DC--DC applications, the NCL30100 can also be used in offline applications, a schematic and PCB layout are provided to illustrate a typical circuit configuration. Input voltage: Vin -- 115 Vac Nominal LED current: 700 mA (rms) LEDripple: 120 mA (peak--to--peak) VLED: 3.2 V Freewheel diode Vf: 0.5 V Target Switching Frequency: 50 kHz Dimming using PWM signal 1 kHz with duty cycle 0 – 99% In this application example, there is schematic and PCB only. The design steps are the same as above mentioned. http://onsemi.com 22 NCL30100 D1 MRA4003 Vac L1 A 100u R1 24k C1 CX1 D3 MRA4003 C2 47n 2.2u 2.2n D4 MRA4003 IC1 NCL30100 R3 150k Vac CS D6 MRA4003 D2 MURA130 R2 24k D5 1N4148 L2 DRV Q1 1mH GND VCC R4 5.6k C3 10p CT C4 560p MTD6N20ET IVC C5 1u R5 R33 DIMM 0/5 V R6 5.6k K Q2 BC817--16L D7 16V GND R7 10k Figure 48. Design Example Schematic of 115 Vac Converter The input voltage in range 85--140 Vac is rectified by bridge rectifier D1, D3, D4 and D6. To limit current peaks generated during on time period, capacitor C1 is used. CX1, C2 and L1 are an EMI filter to protect mains against current spikes mainly generated by D2 if Q1 is turned on. The NCL30100 is powered through resistors R1 and R2. The Vcc voltage is limited by D7. Maximum LED current is set by resistors R3, R4 and R5. In this case Rsense is 0.33 Ω to reach higher accuracy. A small capacitor C3 is used to filter out spikes which are generated during the turn off of diode D2. It is recommended to use L2 with low series resistance since current is flowing through the inductor continuously and D2 should be selected for low forward voltage drop and fast reverse recovery time. Figure 49. Component Side Figure 50. Single Layer PCB Design for this Application http://onsemi.com 23 NCL30100 Figure 51. ILED and Vin Waveform Figure 52. ILED at the Peak of Sinusoidal Voltage http://onsemi.com 24 NCL30100 Figure 53. Input Voltage and Input Current BILL OF MATERIALS FOR THE NCL30100 115 Vac Designator Qty Description Value Tol Footprint Manufacturer Manufacturer Part Number Substitution Allowed Pb--Free C1 1 Capacitor 2.2 mF / 200 V 10% E3.5--8 C2 1 Capacitor 47 nF 10% 1206 Koshin KR1 2.2u 200V 8X11.5 Yes Yes Yageo CC1206KKX7RABB473 Yes Yes C3 1 Capacitor 10 pF 5% C4 1 Capacitor 560 pF 5% 0603 Kemet C0603C100J5GACTU Yes Yes 0603 Kemet C0603C561J5GACTU Yes C5 1 Capacitor 1 mF / 25 V Yes 10% 0805 AVX 08053D105KAT2A Yes Yes D1, D3, D4, D6 4 Standard Recovery Power Rectifier MRA4003T3G -- SMA ON Semiconductor MRA4003T3G No Yes D2 1 Ultrafast Power Rectifier MURA130T3G -- SMA ON Semiconductor MURA130T3G No Yes D5 1 Standard Diode MMSD4148 -- SOD--123 ON Semiconductor MMSD4148T1G No Yes D7 1 Zener Diode 16 V 5% SOD--123 ON Semiconductor MMSZ16VT1G No Yes IC1 1 LED Driver NCL30100 -- TSOP--6 ON Semiconductor NCL30100SNT1G No Yes L1 1 Inductors 100 mH 10% WE--PD4_L Wurth Electronik 7445620 No Yes L2 1 Inductors 1 mH 10% WE--PD_XXL Wurth Electronik 7447709102 No Yes Q1 1 Power MOSFET MTD6N20 -- DPAK ON Semiconductor MTD6N20ET4G No Yes Q2 1 General Purpose Transistor NPN BC817--16 -- SOT--23 ON Semiconductor BC817--16LT1G No Yes Q2 1 Power MOSFET NU -- SOT--23 ON Semiconductor NTS4001NT1G No Yes R1, R2 2 Resistor 24 k 1% 0806 Rohm Semiconductor MCR06EZPFX2402 Yes Yes R3 1 Resistor 150 k 1% 0603 Rohm Semiconductor MCR03EZPFX1503 Yes Yes http://onsemi.com 25 Comments Option NCL30100 BILL OF MATERIALS FOR THE NCL30100 115 Vac Designator Qty Description Value Tol Footprint Manufacturer Manufacturer Part Number Substitution Allowed Pb--Free R4, R6 2 Resistor 5.6 k 1% 0603 Rohm Semiconductor MCR03EZPFX5601 Yes Yes R5 1 Resistor 0.33 R 1% 0805 Welwyn LRCS0805--0R33FT5 Yes Yes R7 1 Resistor 10 k 1% 0603 Rohm Semiconductor MCR03EZPFX1002 Yes Yes CX1 1 EMI Suppression Capacitor 2.2 nF / 300 V 20% XC10B5 Epcos B32021A3222M289 Yes Yes http://onsemi.com 26 Comments NCL30100 PACKAGE DIMENSIONS TSOP--6 CASE 318G--02 ISSUE U D H 6 5 L2 4 E1 GAUGE PLANE E 1 NOTE 5 2 3 L b C DETAIL Z e A 0.05 M SEATING PLANE c A1 DETAIL Z NOTES: 1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M, 1994. 2. CONTROLLING DIMENSION: MILLIMETERS. 3. MAXIMUM LEAD THICKNESS INCLUDES LEAD FINISH. MINIMUM LEAD THICKNESS IS THE MINIMUM THICKNESS OF BASE MATERIAL. 4. DIMENSIONS D AND E1 DO NOT INCLUDE MOLD FLASH, PROTRUSIONS, OR GATE BURRS. MOLD FLASH, PROTRUSIONS, OR GATE BURRS SHALL NOT EXCEED 0.15 PER SIDE. DIMENSIONS D AND E1 ARE DETERMINED AT DATUM H. 5. PIN ONE INDICATOR MUST BE LOCATED IN THE INDICATED ZONE. DIM A A1 b c D E E1 e L L2 M MIN 0.90 0.01 0.25 0.10 2.90 2.50 1.30 0.85 0.20 0 MILLIMETERS NOM MAX 1.00 1.10 0.06 0.10 0.38 0.50 0.18 0.26 3.00 3.10 2.75 3.00 1.50 1.70 0.95 1.05 0.40 0.60 0.25 BSC 10 -- RECOMMENDED SOLDERING FOOTPRINT* 6X 0.60 6X 3.20 0.95 0.95 PITCH DIMENSIONS: MILLIMETERS *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. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC 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 SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner. PUBLICATION ORDERING INFORMATION LITERATURE FULFILLMENT: Literature Distribution Center for ON Semiconductor P.O. Box 5163, Denver, Colorado 80217 USA Phone: 303--675--2175 or 800--344--3860 Toll Free USA/Canada Fax: 303--675--2176 or 800--344--3867 Toll Free USA/Canada Email: [email protected] N. American Technical Support: 800--282--9855 Toll Free USA/Canada Europe, Middle East and Africa Technical Support: Phone: 421 33 790 2910 Japan Customer Focus Center Phone: 81--3--5773--3850 http://onsemi.com 27 ON Semiconductor Website: www.onsemi.com Order Literature: http://www.onsemi.com/orderlit For additional information, please contact your local Sales Representative NCL30100/D