NCP1255GEVB NCP1255 25W Evaluation Board User's Manual http://onsemi.com EVAL BOARD USER’S MANUAL resistive divider. A double hiccup on the VCC brings down the average input power while in auto-recovery fault mode. The NCP1255 features several novelties compared to the NCP1250 previously released. The key feature of this component lies in its ability to push the switching frequency as the converter experiences a sudden power increase. However, this available extra power delivery can only be maintained for a certain amount of time. Beyond this duration, the controller gives up and enters an auto-recovery mode. This mode is perfectly suited for converters supplying highly variable loads such as Haswell-based notebook adapters or inkjet printers to cite a few possible examples. Board Description The application schematic that appears in Figure 1 has been optimized to limit the leakage inductance losses and maximize the efficiency. For this purpose, the RDC clamping network has been replaced by a TVS-based circuitry, leaving enough swing to the 800 V MOSFET. Again, a 600 V type could have been used but would have hampered the drain voltage dynamics at turn off. A capacitor in parallel with the TVS limits its peak current at the switch opening and helps softening the radiated noise. Besides its excellent performance in standby, the TVS approach helps to maintain a safe clamping level given the wide output power excursion. The chip supply is brought in via pin 6. Please note that the start-up resistances, besides cranking the controller, also perform the X2 discharge function for free. Upon start-up, for a voltage less than 18 V (typical), the internal consumption is limited to 15 mA maximum. It suddenly changes to a few mA as the controller starts to drive the 800 V MOSFET at 130 kHz when VCC reaches 18 V. The auxiliary voltage can go down to around 9 V before the controller safely stops the switching pulses. The first VCC capacitor C3 must be sized so that the auxiliary winding takes over before the UVLO is touched. The auxiliary winding is tailored to deliver an auxiliary voltage above 12 V and it drops to 10 V in no-load conditions. This guarantees a good no-load standby power performance as you will read below. A low-valued resistance (R13) limits the voltage excursion on this auxiliary voltage in short circuit situations. Regulation is ensured by pulling down the dedicated pin via an optocoupler, driven from the secondary side by a NCP431. This new device does not require a 1 mA bias current as it was the case with the classical TL431. The absence of this bias current greatly contributes to reducing the no-load standby power. General Description The part is encapsulated in a SOIC−8 package but a reduced-feature set version (no brown-out and timers are internally set), the NCP1254, also exists in a tiny TSOP−6 package. Featuring a low-power BiCMOS process, the die accepts to work with VCC levels up to 35 V, safely clamping the drive voltage below 12 V. With its 15 mA start-up current, a high-value resistive network can be used in offline applications to crank the converter, naturally minimizing the wasted power in high-line conditions. In nominal load operations, the switching frequency of this peak-current mode control circuit is 65 kHz. When the power demand goes up, the controller increases the peak current setpoint until it reaches the upper limit (0.8 V over Rsense, no opp). At this point, the output power demand increase can only be answered by further shifting the switching frequency up until it reaches another limit, 130 kHz. The maximum power is thus obtained at this moment. On the contrary, in light-load operations, the part linearly reduces its switching frequency down to 26 kHz and enters skip cycle as power goes further down. This mode of operation favors higher efficiency from high to moderate output levels and ensures the lowest acoustic noise in the transformer. To improve the EMI signature, a low-frequency modulation brings some dither to the switching pattern. Unlike other circuits, the dither is kept in foldback and peak excursion modes, continuously smoothing the noise signature. The part hosts several new protection means such as an auto-recovery brown-out circuit. It is adjustable via a Semiconductor Components Industries, LLC, 2012 December, 2012 − Rev. 0 1 Publication Order Number: EVBUM2160/D L1 + 2 http://onsemi.com 3 330 kW 3 330 kW 85−260 Vac F1 250 V Type=2AT R35abc 1 MW C12 X2 470 nF 2 27 mH Schaffner RN114−0.8/02 IC4 KBU406 R9abc 1 MW IN − C10 C7 100 mF 47 pF + R15 1 kW R16 331 kW U2B R19 820 kW 220pF C4 C5 1 nF R20 390 kW C15 0.1 mF 1mF C6 R5 80kW 5 6 4 7 3 8 10mF C3 + D3 1N4937 2 1 U1 Eris R14 2.2 MW 2 D1 MUR160 R12 0W C1 33nF 200V 1 6 R24 not wired 1 kW R10 Q2 2N2907 Q1 STP7NK80ZFP R6 22 W 5 R7 4.3 kW D4 1N4148 + C13 47 mF R13 10 W Aux. D6 P6KE220 R2a 1.5 W 0.5 W R2b 1.5 W 0.5 W C8 100 pF 1 kV 11, 12 7, 8 C11 680 pF C2 680 mF + D5 1N973 U2A SFH−615A Figure 1. The Typical Implementation of the NCP1255 in an Isolated Flyback Converter Authorizing Peak Power Excursions Y1 C14 2.2 nF D2 MUR530 R18 80 W U3 NCP431 C9 22 nF R1 2.2 kW R3 1 kW R11 10 kW R17 118 kW 0V 32 V NCP1255PRNGEVB NCP1255PRNGEVB The Specifications 95 The evaluation board must deliver 32 V at a nominal 25 W output power (Iout = 0.8 A). When the frequency increases to 130 kHz, the peak power is up to 35 W or a 40% increase compared to the nominal value. The duration of the peak is set by resistance R7 pulling pin 8 down to ground. When set to 200 ms (tOVL) as in this board, the short circuit duration (tSC) is internally limited to 50 ms: tSC = tOVL/4. Should the output current further grow, as the frequency is clamped, the feedback voltage rises up to its open loop value ( 4.5 V). In this mode, the delivered power increases to 41 W or a 64% peak compared to the 25 W nominal value. The complete power supply specifications are as follows: Vout = 32 V Vin = 100 − 240 V rms Iout, nom = 0.8 A (Continuous Delivery of 25 W) Iout, peak = 1.3 A (Peak Power of 41 W) Fsw, nom = 65 kHz Fsw, max = 130 kHz The transformer is built on a PQ26/25 type of core and features the following characteristics: Primary Inductance LP = 1 mH Maximum Primary Peak Current at TA = 70C = 1.3 A Turns Ratio, Np:Ns = 1:0.39 Turns Ratio, Np:Naux = 1:0.19 Continuous Primary rms Current = 0.8 A Continuous Secondary rms Current = 1.9 A IEC−950 Safety Compliant Vin (100 V rms) 90 hĂ(%) 85 Vin (230 V rms) 80 75 70 65 60 0 5 10 15 20 25 30 Pout (W) Figure 2. The Efficiency is Maintained in Light-load Conditions Thanks to the Frequency Foldback Technique Typical Waveforms Some typical signals have been captured on the operating board. The start-up sequence at a 100 V rms input is clean, exempt from output overshoot (Figure 3): vout (t) Electrical Performance Some efficiency tests were carried on this board. The current was set to its nominal value (0.8 A) and reduced in a 20-step sequence. Efficiency was recorded at every step and collected in Figure 2 graph. As you can see, the nominal efficiency is slightly less than 90% at nominal and maintains above 85% as the output power drops. The average efficiency at a 100 V input is 88.3% and drops slightly less than 85% at high line (230 V rms). Please note that these measurements include a 1.5 m long dc cable. The light and no-load numbers are as follows: vcc (t) Vin = 100 V rms Figure 3. There is No Noticeable Output Voltage Overshoot Upon Start Up at Low Line In short circuit, the double hiccup (Figure 4) nicely reduces the duty cycle in burst mode to less than 3%. This greatly helps to reduce the average input power while in fault mode. The peak power behavior was also tested as shown in Figure 5. In the left side, the peak power is 35 W and lasts 100 ms. The feedback voltage is around 4 V, the controller considers an overload transient. The output voltage drop is well contained in the allowable limits (5%). If the transient load duration is reduced to slightly below 50 ms but the power increased to 41 W, the controller lets the voltage drop while authorizing the peak excursion. Should the duration exceeds 50 ms, the power supply would protect itself and enter hiccup mode. Table 1. LIGHT AND NO-LOAD NUMBERS Low Line, 100 V rms High Line, 230 V rms Pout = 0 W, Pin = 48.7 mW Pout = 0 W, Pin = 100 mW Pout = 0.5 W, Pin = 0.690 W Pout = 0.5 W, Pin = 0.81 W Pout = 0.6 W, Pin = 0.797 W Pout = 0.6 W, Pin = 0.92 W Pout = 0.7 W, Pin = 0.915 W Pout = 0.7 W, Pin = 1.06 W Iout = 0.8 A These numbers are very good, furthermore if we consider a low-voltage IC externally cranked by a resistive network. The brown-out sensing network is another burden that significantly impacts the performance as well. When the start-up/X2 network and the brown-out divider are removed while the converter delivers an unloaded 32 V output, the input consumption is measured at 50 mW with a 230 V rms input voltage. http://onsemi.com 3 NCP1255PRNGEVB VOUT (t) vDS (t) VCC (t) 2.5 s Vin(100 = 100 V rms VIN V rms) vout (t) IOUT (0.8 A) Vin = 100 V rms Iout = 0.5 A Iout,peak = 1.1 A vFB (t) 50 ms vout (t) 1.15 V 3.5% 2s vDS (t) Vin = 265 V rms Vin = 100 V rms Figure 4. The Double Hiccup Nicely Limits the Input Average Power while in Burst Iout = 0.5 A Iout,peak = 1.3 A vFB (t) Figure 5. By Increasing the Switching Frequency Up to 130 kHz, the Controller Authorizes Peak Power for a Certain Amount of Time Conclusion transiently increasing the power capability without affecting the transformer as the peak current remains constant. Packed with a wealth of features, this SOIC package will let you build safe and rugged power converters with a limited count of surrounding components. This evaluation board user’s manual shows the peak power capability offered by the NCP1255 and the overall good efficiency brought by the frequency foldback technique. The frequency excursion offers a nice means of http://onsemi.com 4 NCP1255PRNGEVB Table 2. BILL OF MATERIAL FOR THE NCP1255 EVALUATION BOARD Substitution Allowed Comments Designator Qty. Description Value Tolerance Footprint Manufacturer Manufacturer Part Number R1 1 Resistor 2.2 kW 1% SMD0805 Multicomp MCHP05W4F2201T5E Yes Not Wired R2a, R2b 2 Resistor 1.5 W, 0.5 W 1% SMD2510 Panasonic ERJ1TRQF1R5U Yes 0.5 W R3 1 Resistor 1 kW 1% SMD0805 Multicomp MCHP05W4F1001T5E Yes − R4a, R4B 2 Resistor 15 kW 1% Through-hole Vishay BC Components MRS25000C1503FCT00 Yes 0.6 W R5 1 Resistor 80.6 kW 0.1% SMD0805 TE Connectivity/ Holsworthy RP73D2A80K6BTG Yes − R6 1 Resistor 22 W 1% SMD0805 Multicomp MCHP05W4F220JT5E Yes − R7 1 Resistor 4.3 kW 1% SMD0805 Multicomp MCHP05W4F2202T5E Yes − R9a, R9b, R9c 3 Resistor 330 kW 1% SMD0805 Multicomp MCHP05W4F3303T5E Yes − R10 1 Resistor 1 kW 1% SMD0805 Multicomp MCHP05W4F1001T5E Yes − R11 1 Resistor 10 kW 1% SMD0805 Multicomp MCHP05W4F1002T5E Yes − R12 1 Resistor 0W 1% Through-hole Vishay BC Components MRS25000C2209FCT00 Yes Strapped R13 1 Resistor 10 W 1% Through-hole Vishay BC Components MRS25000C1509FCT00 Yes − R14 1 Resistor 2.2 MW 1% Through-hole Vishay BC Components MRS25000C2204FCT00 Yes 0.6 W R15 1 Resistor 1 kW 1% SMD0805 Multicomp MCHP05W4F1001T5E Yes − R16 1 Resistor 330 kW 1% SMD0805 Multicomp MCHP05W4F3303T5E Yes − R17 1 Resistor 118 kW 0.1% SMD0805 Multicomp MCTC0525B1183T5E Yes − R18 1 Resistor 80.6 kW 1% Through-hole Vishay BC Components MRS25000C8069FCT00 Yes 0.6 W R19 1 Resistor 820 kW 1% Through-hole Vishay BC Components MRS25000C8203FCT00 Yes 0.6 W R20 1 Resistor 390 kW 1% Through-hole Vishay BC Components MRS25000C3903FCT00 Yes 0.6 W R24 1 Resistor 22 kW 1% SMD0805 Multicomp MCHP05W4F2202T5E Yes Not Wired R35a, R35b, R35c 3 Resistor 330 kW 1% SMD0805 Multicomp MCHP05W4F3303T5E Yes − C1 1 Capacitor 33 nF/250 V 10% Through-hole Vishay MKT 1822−333//405 Yes − C2 1 Electrolytic Capacitor 680 mF/35 V 20% Through-hole Rubycon 35ZL680MEFC12.5X20 Yes − C3 1 Capacitor 10 mF/50 V 10% Radial Panasonic ECA1HHG100 Yes − C4 1 Capacitor 220 pF 5% SMD0805 Multicomp MCCA000335 Yes − C5 1 Capacitor 1 nF 5% SMD0805 Multicomp MCCA000351 Yes − C5a 1 Capacitor 470 pF 5% SMD0805 Multicomp MCCA000342 Yes − C6 1 Electrolytic Capacitor 1 mF/16 V 20% Radial Murata MURGRM31MR71C105K A01L Yes − C7 1 Electrolytic Capacitor 100 mF/400 V 20% Through-hole Nichicon UCY2G101MHD Yes − C8 1 Capacitor 100 pF/1 kV 20% Through-hole Vishay F101K25S3NN63J5R Yes − C9 1 Capacitor 22 nF 10% SMD0805 Multicomp MCCA000374 Yes − C10 1 Capacitor 47 pF 5% SMD0805 Multicomp MCCA000326 Yes − C11 1 Capacitor 680 pF/100 V 10% Through-hole Vishay BC Components D681K20Y5PH63L2R Yes − C12 1 Capacitor 470 nF 10% Radial Epcos B32923C3474K Yes X2 C13 1 Capacitor 47 mF/25 V 20% Radial Panasonic ECEA1HN470U Yes − C14 1 Capacitor 2.2 nF/250 V 20% Radial Murata DE1E3KX222MA5B Yes Y1 C15 1 Capacitor 0.1 mF 10% SMD0805 AVX 08051C104K4T2A Yes − D1 1 Ultra-fast Diode MUR160 − Axial ON Semiconductor MUR160RLG Yes − D2 1 Rectifier MURD530 − DPAK−4 ON Semiconductor − No − http://onsemi.com 5 NCP1255PRNGEVB Table 2. BILL OF MATERIAL FOR THE NCP1255 EVALUATION BOARD (continued) Substitution Allowed Comments Designator Qty. Description Value Tolerance Footprint Manufacturer Manufacturer Part Number D3 1 Rectifier 1N4937 − Axial ON Semiconductor 1N4937RLG No − D4 1 Rectifier 1N4148 − Axial Fairchild Semiconducotr FDLL4148 Yes − D5 1 Zener Diode 1N973 − SMDSOD80 NTE Electronics 1N973B No 33 V Zener D6 1 TVS P6KE220A − DO15 Fairchild Semiconducotr P6KE220A Yes − F1 1 Socket forUse PCB TR5 TE5 − Radial Wickmann 5590000000 − − F1 1 Fuse 2 A/250 V−T − Radial Schurter 0034.6618 1 (Note 1) Yes − U1 1 PWM Controller NCP1255 − SOIC8 ON Semiconductor − (Note 1) No − U2 1 Optocoupler SF615A−2 − SMD Vishay Semiconductor SFH615A−4 (Note 1) No − U3 1 Shunt Regulator NCP431 − SMD − NCP431ACSNT1G No SOT−23 U4 1 Diode Bridge KBU4K − Through-hole Multicomp KBU4K Yes − TR1 1 Transformer 750313495 − Through-hole Würth Electronic Midcom 750313495 No PQ2625 J1 1 Line Input Connector C8 SNAP IN 2P − Through-hole Schurter 4300.0099 − − J2 1 Output Voltage Connector − − Through-hole Taiwan Semiconductor KBU406 − − Q1 1 HV MOSFET STP7NK80ZFP − TO220 ST Microelectronics STP7NK80ZFP − − Q2 1 PNP Transistor PMBT2907A − SOT23 NXP PMBT2907A − − L1 1 Self 227 mH RN114−0.8−02 − Through-hole Schaffner RN114−0.8−02 − − J2 1 PCB Terminal Block CTB5000/2 − Through-hole Camden CTB5000/2 − − Holes 4 Plastic Feet SFCBS−M4− 16M−01 − Through-hole Richco SFCBS−M4−16M−01 − − 1. This is a Pb-free device. http://onsemi.com 6 NCP1255PRNGEVB TRANSFORMER SPECIFICATIONS ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). 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. SCILLC reserves the right to make changes without further notice to any products herein. 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