NCP1271 Soft−Skipt Mode Standby PWM Controller with Adjustable Skip Level and External Latch The NCP1271 represents a new, pin to pin compatible, generation of the successful 7−pin current mode NCP12XX product series. The controller allows for excellent stand by power consumption by use of its adjustable Soft−Skip mode and integrated high voltage startup FET. This proprietary Soft−Skip also dramatically reduces the risk of acoustic noise. This allows the use of inexpensive transformers and capacitors in the clamping network. Internal frequency jittering, ramp compensation, timer−based fault detection and a latch input make this controller an excellent candidate for converters where ruggedness and component cost are the key constraints. http://onsemi.com MARKING DIAGRAMS 8 SOIC−7 D SUFFIX CASE 751U 1 x Features • Fixed−Frequency Current−Mode Operation with Ramp • • • • • • • • • • • Compensation and Skip Cycle in Standby Condition Timer−Based Fault Protection for Improved Overload Detection “Soft−Skip Mode” Technique for Optimal Noise Control in Standby Internal High−Voltage Startup Current Source for Lossless Startup "5% Current Limit Accuracy over the Full Temperature Range Adjustable Skip Level Internal Latch for Easy Implementation of Overvoltage and Overtemperature Protection Frequency Jittering for Softened EMI Signature +500 mA/−800 mA Peak Current Drive Capability Sub−100 mW Standby Power can be Achieved Pin−to−Pin Compatible with the Existing NCP120X Series This is a Pb−Free Device 1271x ALYWG G A L Y W G = A or B A= 65 kHz B= 100 kHz = Assembly Location = Wafer Lot = Year = Work Week = Pb−Free Package (Note: Microdot may be in either location) PIN CONNECTIONS SOIC−7 Skip/latch FB CS GND 1 8 HV 2 3 6 4 5 VCC Drv (Top View) ORDERING INFORMATION Typical Applications See detailed ordering and shipping information in the package dimensions section on page 18 of this data sheet. • AC−DC Adapters for Notebooks, LCD Monitors • Offline Battery Chargers • Consumer Electronic Appliances STB, DVD, DVDR *For additional information on our Pb−Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D. © Semiconductor Components Industries, LLC, 2006 December, 2006 − Rev. 2 1 Publication Order Number: NCP1271/D NCP1271 + AC Input Output Voltage EMI Filter − latch input* skip/latch HV FB Vcc CS Drv Gnd *Optional R*ramp NCP1271 Rskip Figure 1. Typical Application Circuit MAXIMUM RATINGS (Notes 1 and 2) Symbol Value Unit VCC Pin (Pin 6) Maximum Voltage Range Maximum Current Vmax Imax −0.3 to +20 100 V mA Skip/Latch, FB, CS Pin (Pins 1−3) Maximum Voltage Range Maximum Current Vmax Imax −0.3 to +10 100 V mA Drv Pin (Pin 5) Maximum Voltage Range Maximum Current Vmax Imax −0.3 to +20 −800 to +500 V mA HV Pin (Pin 8) Maximum Voltage Range Maximum Current Vmax Imax −0.3 to +500 100 V mA Power Dissipation and Thermal Characteristics Thermal Resistance, Junction−to−Air, SO−7, Low Conductivity PCB (Note 3) Thermal Resistance, Junction−to−Lead, SO−7, Low Conductivity PCB Thermal Resistance, Junction−to−Air, SO−7, High Conductivity PCB (Note 4) Thermal Resistance, Junction−to−Lead, SO−7, High Conductivity PCB RqJA RqJL RqJA RqJL 177 75 136 69 °C/W °C/W °C/W °C/W Operating Junction Temperature Range TJ −40 to +125 °C Maximum Storage Temperature Range Tstg −60 to +125 °C Rating 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 contains ESD protection and exceeds the following tests: Pins 1−6: Human Body Model 2000 V per Mil−Std−883, Method 3015 Machine Model Method 150 V (on Pins 5 and 6) and 200 V (all other pins) Pin 8 is the HV startup of the device and is rated to the maximum rating of the part, or 500 V This device contains latchup protection and exceeds 100 mA per JEDEC Standard JESD78. 2. Guaranteed by design, not tested. 3. As mounted on a 40x40x1.5 mm FR4 substrate with a single layer of 80 mm2 of 2 oz copper traces and heat spreading area. As specified for a JEDEC 51 low conductivity test PCB. Test conditions were under natural convection or zero air flow. 4. As mounted on a 40x40x1.5 mm FR4 substrate with a single layer of 650 mm2 of 2 oz copper traces and heat spreading area. As specified for a JEDEC 51 high conductivity test PCB. Test conditions were under natural convection or zero air flow. http://onsemi.com 2 NCP1271 8V I skip Skip/ latch − + 1 13 us filter latch−off, reset when Vcc < 4V S R Rskip 10V Vskip = Rskip * Iskip or Vskip = 1.2 V when pin 1 is opened 4.8 V 2.85 V 2 1/3 V FB / 3 0 CS V PWM V CS 180 ns LEB 3 PWM − + turn off 12.6/ 5.8 V soft−skip S Q R soft start short circuit fault − + UVLO double hiccup B2 Counter 9.1 V − + & 10V R ramp skip + − Vss Soft start/ soft−skip (1V max) management 4 ms/ 300 us − + 130ms delay & 1 75.3k 10V disable soft skip TLD − + 16.7k V FB FB R CS V CC 6 20V 100uA 0 jittered ramp current source HV 4.1 mA when Vcc > 0.6 V 0.2 mA when Vcc < 0.6 V V skip V FB 8 Q turn on internal bias OR V CC Drv 4 1 R 7.5% Jittering 65, 100 kHz Oscillator 0 Gnd Q S Max duty = 80% driver: +500 mA / −800 mA 5 Figure 2. Functional Block Diagram PIN FUNCTION DESCRIPTION Pin No. Symbol Function Description 1 Skip/latch Skip Adjust or Latchoff A resistor to ground provides the adjustable standby skip level. Additionally, if this pin is pulled higher than 8.0 V (typical), the controller latches off the drive. 2 FB Feedback An optocoupler collector pulls this pin low during regulation. If this voltage is less than the Skip pin voltage, then the driver is pulled low and Soft−Skip mode is activated. If this pin is open (>3 V) for more than 130 ms, then the controller is placed in a fault mode. 3 CS Current Sense This pin senses the primary current for PWM regulation. The maximum primary current is limited to 1.0 V / RCS where RCS is the current sense resistor. Additionally, a ramp resistor Rramp between the current sense node and this pin sets the compensation ramp for improved stability. 4 Gnd IC Ground 5 Drv Driver Output 6 VCC Supply Voltage 8 HV High Voltage − The NCP1271’s powerful output is capable of driving the gates of large Qg MOSFETs. This is the positive supply of the device. The operating range is between 10 V (min) and 20 V (max) with a UVLO start threshold 12.6 V (typ). This pin provides (1) Lossless startup sequence (2) Double hiccup fault mode (3) Memory for latch−off shutdown and (4) Device protection if VCC is shorted to GND. http://onsemi.com 3 NCP1271 ELECTRICAL CHARACTERISTICS (For typical values TJ = 25°C, for min/max values, TJ = −40°C to +125°C, VCC = 14 V, HV = open, skip = open, FB = 2 V, CS = Ground, DRV = 1 nF, unless otherwise noted.) Pin Symbol Min Typ Max Unit Oscillation Frequency (65 kHz Version, TJ = 25_C) Oscillation Frequency (65 kHz Version, TJ = −40 to + 85_C) Oscillation Frequency (65 kHz Version, TJ = −40 to + 125_C) Oscillation Frequency (100 kHz Version, TJ = 25_C) Oscillation Frequency (100 kHz Version, TJ = −40 to +85_C) Oscillation Frequency (100 kHz Version, TJ = −40 to +125_C) 5 fosc 61.75 58 55 95 89 85 65 65 65 100 100 100 68.25 69 69 105 107 107 kHz Oscillator Modulation Swing, in Percentage of fosc 5 − − "7.5 − % Oscillator Modulation Swing Period 5 − − 6.0 − ms Maximum Duty Cycle (VCS = 0 V, VFB = 2.0 V) 5 Dmax 75 80 85 % ROH ROL 6.0 2.0 11 6.0 20 12 Characteristic OSCILLATOR GATE DRIVE W Gate Drive Resistance Output High (VCC = 14 V, Drv = 300 W to Gnd) Output Low (VCC = 14 V, Drv = 1.0 V) 5 Rise Time from 10% to 90% (Drv = 1.0 nF to Gnd) 5 tr − 30 − ns Fall Time from 90% to 10% (Drv = 1.0 nF to Gnd) 5 tf − 20 − ns Maximum Current Threshold 3 ILimit 0.95 1.0 1.05 V Soft−Start Duration − tSS − 4.0 − ms Soft−Skip Duration − tSK − 300 − ms Leading Edge Blanking Duration 3 tLEB 100 180 330 ns Propagation Delay (Drv =1.0 nF to Gnd) − − − 50 150 ns Ramp Current Source Peak 3 Iramp(H) − 100 − mA Ramp Current Source Valley 3 Iramp(L) − 0 − mA Default Standby Skip Threshold (Pin 1 = Open) 2 Vskip − 1.2 − V Skip Current (Pin 1 = 0 V, TJ = 25_C) 1 Iskip 26 43 56 mA Skip Level Reset (Note 5) 1 Vskip−reset 5.0 5.7 6.5 V Transient Load Detection Level to Disable Soft−Skip Mode 2 VTLD 2.6 2.85 3.15 V Latch Protection Threshold 1 Vlatch 7.1 8.0 8.7 V Latch Threshold Margin (Vlatch−m = VCC(off) − Vlatch) 1 Vlatch−m 0.6 1.2 − V Noise Filtering Duration 1 − − 13 − ms Propagation Delay (Drv = 1.0 nF to Gnd) 1 Tlatch − 100 − ns 2 tprotect − 130 − ms CURRENT SENSE SKIP EXTERNAL LATCH SHORT−CIRCUIT FAULT PROTECTION Time for Validating Short−Circuit Fault Condition 5. Please refer to Figure 39 for detailed description. 6. Guaranteed by design. http://onsemi.com 4 NCP1271 ELECTRICAL CHARACTERISTICS (continued) (For typical values TJ = 25°C, for min/max values, TJ = −40°C to +125°C, VCC = 14 V, HV = open, skip = open, FB = 2 V, CS = Ground, DRV = 1 nF, unless otherwise noted.) Characteristic Pin Symbol Min Typ Max Unit High−Voltage Current Source Inhibit Voltage (ICC = 200 mA, HV = 50 V) Inhibit Current (VCC = 0 V, HV = 50 V) Startup (VCC = VCC(on) − 0.2 V, HV = 50 V) Leakage (VCC = 14 V, HV = 500 V) 6 6 6 8 Vinhibit Iinhibit IHV IHV−leak 190 80 3.0 10 600 200 4.1 25 800 350 6.0 50 mV mA mA mA Minimum Startup Voltage (VCC = VCC(on) – 0.2 V, ICC = 0.5 mA) 8 VHV(min) − 20 28 V VCC(on) VCC(off) VCC(on) − VCC(off) VCC(latch) VCC(reset) 11.2 8.2 3.0 5.0 − 12.6 9.1 3.6 5.8 4.0 13.8 10 4.2 6.5 − V V V V V ICC1 ICC1 ICC2 ICC3 − − − − 2.3 3.1 1.3 500 3.0 3.5 2.0 720 mA mA mA mA STARTUP CURRENT SOURCE SUPPLY SECTION VCC Regulation Startup Threshold, VCC Increasing Minimum Operating Voltage After Turn−On VCC Operating Hysteresis Undervoltage Lockout Threshold Voltage, VCC Decreasing Logic Reset Level (VCC(latch) –VCC(reset) > 1.0 V) (Note 7) 6 VCC Supply Current Operating (VCC = 14 V, 1.0 nF Load, VFB = 2.0 V, 65 kHz Version) Operating (VCC = 14 V, 1.0 nF Load, VFB = 2.0 V, 100 kHz Version) Output Stays Low (VCC = 14 V, VFB = 0 V) Latchoff Phase (VCC = 7.0 V, VFB = 2.0 V) 6 7. Guaranteed by design. TYPICAL CHARACTERISTICS 85 84 100 MAXIMUM DUTY CYCLE (%) OSCILLATION FREQUENCY (kHz) 110 100 kHz 90 80 70 65 kHz 60 83 82 81 80 79 78 77 76 50 −50 −25 0 25 50 75 100 75 −50 125 −25 0 25 50 75 100 TEMPERATURE (°C) TEMPERATURE (°C) Figure 3. Oscillation Frequency vs. Temperature Figure 4. Maximum Duty Cycle vs. Temperature http://onsemi.com 5 125 NCP1271 16 1.04 14 ROH 12 1.02 CURRENT LIMIT (V) OUTPUT GATE DRIVE RESISTANCE (W) TYPICAL CHARACTERISTICS 10 8 6 ROL 4 0.98 0.96 2 0 −50 −25 0 25 50 75 100 0.94 −50 125 −25 0 25 50 75 100 TEMPERATURE (°C) TEMPERATURE (°C) Figure 5. Output Gate Drive Resistance vs. Temperature Figure 6. Current Limit vs. Temperature 125 350 LEADING EDGE BLANKING TIME (ns) 8 SOFT−START DURATION (ms) 1.0 7 6 5 4 3 2 1 0 −50 −25 0 25 50 75 100 125 300 250 200 150 100 50 0 −50 −25 0 25 50 75 100 TEMPERATURE (°C) TEMPERATURE (°C) Figure 7. Soft−Start Duration vs. Temperature Figure 8. Leading Edge Blanking Time vs. Temperature 1.40 125 45 SKIP PIN CURRENT (mA) DEFAULT SKIP LEVEL (V) 44 1.30 1.20 1.10 43 42 41 40 39 38 37 36 1.00 −50 −25 0 25 50 75 100 35 −50 125 −25 0 25 50 75 100 TEMPERATURE (°C) TEMPERATURE (°C) Figure 9. Default Skip Level vs. Temperature Figure 10. Skip Pin Current vs. Temperature http://onsemi.com 6 125 NCP1271 6.0 TRANSIENT LOAD DETECT LEVEL (V) SKIP LEVEL RESET THRESHOLD (V) TYPICAL CHARACTERISTICS 5.9 5.8 5.7 5.6 5.5 −50 −25 0 25 50 75 100 125 3.0 2.9 2.8 2.7 2.6 2.5 −50 −25 0 8.5 150 8.4 145 8.3 8.2 8.1 8.0 7.9 7.8 7.7 7.6 0 25 50 75 100 125 135 130 125 120 115 110 105 −25 0 25 50 75 100 TEMPERATURE (°C) TEMPERATURE (°C) Figure 13. Latch Protection Level vs. Temperature Figure 14. Fault Validation Time vs. Temperature 125 300 0.9 STARTUP INHIBIT CURRENT (mA) STARTUP INHIBIT VOLTAGE (V) 100 140 100 −50 125 1.0 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 −50 75 Figure 12. Transient Load Detection Level vs. Temperature FAULT VALIDATION TIME (ms) LATCH PROTECTION LEVEL (V) Figure 11. Skip Level Reset Threshold vs. Temperature −25 50 TEMPERATURE (°C) TEMPERATURE (°C) 7.5 −50 25 −25 0 25 50 75 100 VCC = 0 V 250 200 150 100 50 0 −50 125 −25 0 25 50 75 100 TEMPERATURE (°C) TEMPERATURE (°C) Figure 15. Startup Inhibit Voltage vs. Temperature Figure 16. Startup Inhibit Current vs. Temperature http://onsemi.com 7 125 NCP1271 TYPICAL CHARACTERISTICS 4.5 6 VCC = VCC(on) − 0.2 V STARTUP CURRENT (mA) STARTUP CURRENT (mA) 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 5 125°C 4 −40°C 25°C 3 2 1 3.6 3.5 −50 0 −25 0 25 50 75 100 125 0 8 12 Figure 18. Startup Current vs. VCC Voltage 25 35 30 25 20 15 10 5 −25 0 25 50 75 100 24 23 22 21 20 19 18 17 16 15 −50 125 −25 0 25 50 75 100 125 TEMPERATURE (°C) Figure 19. Startup Leakage Current vs. Temperature Figure 20. Minimum Startup Voltage vs. Temperature 3.5 14 VCC(on) ICC1 (100 kHz) 3.0 10 SUPPLY CURRENT (mA) 12 VCC(off) 8 VCC(latch) 6 VCC(reset) 4 2 0 −50 10 Figure 17. High Voltage Startup Current vs. Temperature TEMPERATURE (°C) SUPPLY VOLTAGE THRESHOLD (V) 6 VCC, SUPPLY VOLTAGE (V) MINIMUM STARTUP VOLTAGE (V) STARTUP LEAKAGE CURRENT (mA) 4 TEMPERATURE (°C) 40 0 −50 2 2.5 ICC1 (65 kHz) 2.0 1.5 ICC2 1.0 ICC3 0.5 −25 0 25 50 75 100 0 −50 125 −25 0 25 50 75 100 TEMPERATURE (°C) TEMPERATURE (°C) Figure 21. Supply Voltage Thresholds vs. Temperature Figure 22. Supply Currents vs. Temperature http://onsemi.com 8 125 NCP1271 OPERATING DESCRIPTION • Current−Mode Operation: The NCP1271 uses Introduction The NCP1271 represents a new generation of the fixed−frequency PWM current−mode flyback controllers from ON Semiconductor. The device features integrated high−voltage startup and excellent standby performance. The proprietary Soft−Skip Mode achieves extremely low−standby power consumption while keeping power supply acoustic noise to a minimum. The key features of the NCP1271 are as follows: • Timer−Based Fault Detection: In the event that an abnormally large load is applied to the output for more than 130 ms, the controller will safely shut the application down. This allows accurate overload (OL) or short−circuit (SC) detection which is not dependent on the auxiliary winding. • Soft−Skip Mode: This proprietary feature of the NCP1271 minimizes the standby low−frequency acoustic noise by ramping the peak current envelope whenever skip is activated. • Adjustable Skip Threshold: This feature allows the power level at which the application enters skip to be fully adjusted. Thus, the standby power for various applications can be optimized. The default skip level is 1.2 V (40% of the maximum peak current). • 500 V High−Voltage Startup Capability: This AC−DC application friendly feature eliminates the need for an external startup biasing circuit, minimizes the standby power loss, and saves printed circuit board (PCB) space. • Dual High−Voltage Startup−Current Levels: The NCP1271 uniquely provides the ability to reduce the startup current supply when Vcc is low. This prevents damage if Vcc is ever shorted to ground. After Vcc rises above approximately 600 mV, the startup current increases to its full value and rapidly charges the Vcc capacitor. • Latched Protection: The NCP1271 provides a pin, which if pulled high, places the part in a latched off mode. Therefore, overvoltage (OVP) and overtemperature (OTP) protection can be easily implemented. A noise filter is provided on this function to reduce the chances of falsely triggering the latch. The latch is released when Vcc is cycled below 4 V. • Non−Latched Protection/ Shutdown Option: By pulling the feedback pin below the skip threshold level, a non−latching shutdown mode can be easily implemented. • 4.0 ms Soft−Start: The soft start feature slowly ramps up the drive duty cycle at startup. This forces the primary current to also ramp up slowly and dramatically reduces the stress on power components during startup. • • • • current−mode control which provides better transient response than voltage−mode control. Current−mode control also inherently limits the cycle−by−cycle primary current. Compensation Ramp: A drawback of current−mode regulation is that the circuit may become unstable when the operating duty cycle is too high. The NCP1271 offers an adjustable compensation ramp to solve this instability. 80% Maximum Duty Cycle Protection: This feature limits the maximum on time of the drive to protect the power MOSFET from being continuously on. Frequency Jittering: Frequency jittering softens the EMI signature by spreading out peak energy within a band +/− 7.5% from the center frequency. Switching Frequency Options: The NCP1271 is available in either 65 kHz or 100 kHz fixed frequency options. Depending on the application, the designer can pick the right device to help reduce magnetic switching loss or improve the EMI signature before reaching the 150 kHz starting point for more restrictive EMI test limits. NCP1271 Operating Conditions There are 5 possible operating conditions for the NCP1271: 1. Normal Operation – When VCC is above VCC(off) (9.1 V typical) and the feedback pin voltage (VFB) is within the normal operation range (i.e.,VFB < 3.0 V), the NCP1271 operates as a fixed−frequency current−mode PWM controller. 2. Standby Operation (or Skip−Cycle Operation) When the load current drops, the compensation network responds by reducing the primary peak current. When the peak current reaches the skip peak current level, the NCP1271 enters Soft−Skip operation to reduce the power consumption. This Soft−Skip feature offers a modified peak current envelope and hence also reduces the risk of audible noise. In the event of a sudden load increase, the transient load detector (TLD) disables Soft−Skip and applies maximum power to bring the output into regulation as fast as possible. 3. Fault Operation – When no feedback signal is received for 130 ms or when VCC drops below VCC(off) (9.1 V typical), the NCP1271 recognizes it as a fault condition. In this fault mode, the Vcc voltage is forced to go through two cycles of slowly discharging and charging. This is known as a “double hiccup.” The double hiccup insures that ample time is allowed between restarts to prevent overheating of the power devices. If the fault is http://onsemi.com 9 NCP1271 cleared after the double hiccup, then the application restarts. If not, then the process is repeated. 4. Latched Shutdown – When the Skip/latch pin (Pin 1) voltage is pulled above 8.0 V for more than 13 ms, the NCP1271 goes into latchoff shutdown. The output is held low and VCC stays in hiccup mode until the latch is reset. The reset can only occur if Vcc is allowed to fall below VCC(reset) (4.0 V typical). This is generally accomplished by unplugging the main input AC source. 5. Non−Latched Shutdown – If the FB pin is pulled below the skip level, then the device will enter a non−latched shutdown mode. This mode disables the driver, but the controller automatically recovers when the pulldown on FB is released. Alternatively, Vcc can also be pulled low (below 190 mV) to shutdown the controller. This has the added benefit of placing the part into a low current consumption mode for improved power savings. Startup current 4.1 mA 200 uA VCC(on) VCC(latch) 0.6 V VCC Figure 23. Startup Current at Various VCC Levels VCC Double Hiccup Mode Figure 24 illustrates the block diagram of the startup circuit. An undervoltage lockout (UVLO) comparator monitors the VCC supply voltage. If VCC falls below VCC(off), then the controller enters “double hiccup mode.” Vbulk Biasing the Controller During startup, the Vcc bias voltage is supplied by the HV Pin (Pin 8). This pin is capable of supporting up to 500 V, so it can be connected directly to the bulk capacitor. Internally, the pin connects to a current source which rapidly charges VCC to its VCC(on) threshold. After this level is reached, the controller turns on and the transformer auxiliary winding delivers the bias supply voltage to VCC. The startup FET is then turned off, allowing the standby power loss to be minimized. This in−chip startup circuit minimizes the number of external components and Printed Circuit Board (PCB) area. It also provides much lower power dissipation and faster startup times when compared to using startup resistors to VCC. The auxiliary winding needs to be designed to supply a voltage above the VCC(off) level but below the maximum VCC level of 20 V. For added protection, the NCP1271 also include a dual startup mode. Initially, when VCC is below the inhibit voltage Vinhibit (600 mV typical), the startup current source is small (200 uA typical). The current goes higher (4.1 mA typical) when VCC goes above Vinhibit. This behavior is illustrated in Figure 23. The dual startup feature protects the device by limiting the maximum power dissipation when the VCC pin (Pin 6) is accidentally grounded. This slightly increases the total time to charge VCC, but it is generally not noticeable. HV 8 10−to−20V biasing voltage (available after startup) 4.1 mA when Vcc > 0.6 V 200 uA when Vcc < 0.6 V turn off Q S UVLO + − R 12.6/ 5.8 V double hiccup B2 Counter 9.1 V − + & Vcc 6 20V turn on internal bias Figure 24. VCC Management During double hiccup operation, the Vcc level falls to VCC(latch) (5.8 V typical). At this point, the startup FET is turned back on and charges VCC to VCC(on) (12.6 V typical). VCC then slowly collapses back to the VCC(latch) level. This cycle is repeated twice to minimize power dissipation in http://onsemi.com 10 NCP1271 external components during a fault event. After the second cycle, the controller tries to restart the application. If the restart is not successful, then the process is repeated. During this mode, VCC never drops below the 4 V latch reset level. Therefore, latched faults will not be cleared unless the application is unplugged from the AC line (i.e., Vbulk discharges). Figure 25 shows a timing diagram of the VCC double hiccup operation. Note that at each restart attempt, a soft start is issued to minimize stress. Vout VCC 12.6 V 9.1 V t startup 0.6 V time Output waveforms with a large enough VCC capacitor Desired level of Vout Supply voltage, VCC 12.6 V 9.1 V 5.8 V 12.6 V 9.1 V VCC 5.8 V 0.6 V Vout time Output waveforms with too small of a VCC capacitor time Figure 26. Different Startup Scenarios of the Circuits with Different VCC Capacitors Drain current, ID t startup time It is highly recommended that the VCC capacitor be as close as possible to the VCC and ground pins of the product to reduce switching noise. A small bypass capacitor on this pin is also recommended. If the switching noise is large enough, it could potentially cause VCC to go below VCC(off) and force a restart of the controller. It is also recommended to have a margin between the winding bias voltage and VCC(off) so that all possible transient swings of the auxiliary winding are allowed. In standby mode, the VCC voltage swing can be higher due to the low−frequency skip−cycle operation. The VCC capacitor also affects this swing. Figure 27 illustrates the possible swings. Switching is missing in every two VCC hiccup cycles featuring a “double−hiccup” Figure 25. VCC Double Hiccup Operation in a Fault Condition VCC Capacitor As stated earlier, the NCP1271 enters a fault condition when the feedback pin is open (i.e. FB is greater than 3 V) for 130 ms or VCC drops below VCC(off) (9.1 V typical). Therefore, to take advantage of these features, the VCC capacitor needs to be sized so that operation can be maintained in the absence of the auxiliary winding for at least 130 ms. The controller typically consumes 2.3 mA at a 65 kHz frequency with a 1 nF switch gate capacitance. Therefore, to ensure at least 130 ms of operation, equation 1 can be used to calculate that at least an 85 mF capacitor would be necessary. Supply voltage, VCC 9.1 V time C DV 85 mF · (12.6 V−9.1 V) tstartup + VCC + + 130 ms ICC1 2.3 mA Feedback pin voltage, VFB (eq. 1) Vskip If the 130 ms timer feature will not be used, then the capacitance value needs to at least be large enough for the output to charge up to a point where the auxiliary winding can supply VCC. Figure 26 describes different startup scenarios with different VCC capacitor values. If the VCC cap is too small, the application fails to start because the bias supply voltage cannot be established before VCC is reduced to the VCC(off) level. time Drain current, ID time Figure 27. Timing Diagram of Standby Condition http://onsemi.com 11 NCP1271 Soft−Start Operation Figures 28 and 29 show how the soft−start feature is included in the pulse−width modulation (PWM) comparator. When the NCP1271 starts up, a soft−start voltage VSS begins at 0 V. VSS increases gradually from 0 V to 1.0 V in 4.0 ms and stays at 1.0 V afterward. This voltage VSS is compared with the divided−by−3 feedback pin voltage (VFB/3). The lesser of VSS and (VFB/3) becomes the modulation voltage VPWM in the PWM duty cycle generation. Initially, (VFB/3) is above 1.0 V because the output voltage is low. As a result, VPWM is limited by the soft start function and slowly ramps up the duty cycle (and therefore the primary current) for the initial 4.0 ms. This provides a greatly reduced stress on the power devices during startup. V SS Current−Mode Pulse−Width Modulation The NCP1271 uses a current−mode fixed−frequency PWM with internal ramp compensation. A pair of current sense resistors RCS and Rramp sense the flyback drain current ID. As the drain current ramps up through the inductor and current sense resistor, a corresponding voltage ramp is placed on the CS pin (pin 3). This voltage ranges from very low to as high as the modulation voltage VPWM (maximum of 1.0 V) before turning the drive off. If the internal current ramp is ignored (i.e., Rramp ≈ 0) then the maximum possible drain current ID(max) is shown in Equation 2. This sets the primary current limit on a cycle by cycle basis. ID(max) + 1 V RCS (eq. 2) − + VFB/ 3 0 Vbulk 1 I ramp VPWM Figure 28. VPWM is the lesser of VSS and (VFB/3) Q R S − + PWM Output 180ns LEB VCS CS Rramp I D 80% max duty VPWM (1V max. signal) Clock 1 Soft−start voltage, VSS 3 0 RCS 1V Figure 30. Current−Mode Implementation time 4 ms PWM Output Feedback pin voltage divided−by−3, VFB/3 VPWM 1V VCS time must be less than130 ms to prevent fault condition time clock Pulse Width Modulation voltage, VPWM Figure 31. Current−Mode Timing Diagram 1V 4 ms The timing diagram of the PWM is in Figure 31. An internal clock turns the Drive Output (Pin 5) high in each switching cycle. The Drive Output goes low when the CS (Pin 3) voltage VCS intersects with the modulation voltage VPWM. This generates the pulse width (or duty cycle). The maximum duty cycle is limited to 80% (typically) in the output RS latch. time Drain Current, ID 4 ms time Figure 29. Soft−Start (Time = 0 at VCC = VCC(on)) http://onsemi.com 12 NCP1271 Ramp Compensation Ramp compensation is a known mean to cure subharmonic oscillations. These oscillations take place at half the switching frequency and occur only during continuous conduction mode (CCM) with a duty−cycle greater than 50%. To lower the current loop gain, one usually injects between 50 and 75% of the inductor down slope. The NCP1271 generates an internal current ramp that is synchronized with the clock. This current ramp is then routed to the CS pin. Figures 32 and 33 depict how the ramp is generated and utilized. Ramp compensation is simply formed by placing a resistor, Rramp, between the CS pin and the sense resistor. 43 mVńms Rramp + + 5.3 kW 8.1 mAńms (eq. 4) It is recommended that the value of Rramp be limited to less then 10 kW. Values larger than this will begin to limit the effective duty cycle of the controller and may result in reduced transient response. Frequency Jittering Frequency jittering is a method used to soften the EMI signature by spreading the energy in the vicinity of the main switching component. The NCP1271 switching frequency ranges from +7.5% to −7.5% of the switching frequency in a linear ramp with a typical period of 6 ms. Figure 34 demonstrates how the oscillation frequency changes. Ramp current, Iramp Oscillator Frequency 100uA 107.5 kHz 100 kHz time 0 92.5 kHz 80% of period 6 ms 100% of period Figure 32. Internal Ramp Current Source time Figure 34. Frequency Jittering (The values are for the 100 kHz frequency option) DRIVE Clock Fault Detection Figure 35 details the timer−based fault detection circuitry. When an overload (or short circuit) event occurs, the output voltage collapses and the optocoupler does not conduct current. This opens the FB pin (pin 2) and VFB is internally pulled higher than 3.0 V. Since (VFB/3) is greater than 1 V, the controller activates an error flag and starts a 130 ms timer. If the output recovers during this time, the timer is reset and the device continues to operate normally. However, if the fault lasts for more than 130 ms, then the driver turns off and the device enters the VCC Double Hiccup mode discussed earlier. At the end of the double hiccup, the controller tries to restart the application. 100 mA Peak Current Ramp CS Rramp Oscillator Rsense Figure 33. Inserting a Resistor in Series with the Current Sense Information brings Ramp Compensation For the NCP1271, the current ramp features a swing of 100 mA. Over a 65 kHz frequency with an 80% max duty cycle, that corresponds to an 8.1 mA/ms ramp. For a typical flyback design, let’s assume that the primary inductance (Lp) is 350 mH, the SMPS output is 19 V, the Vf of the output diode is 1 V and the Np:Ns ratio is 10:1. The OFF time primary current slope is given by: 4.8V FB 2 V FB V FB 3 Np (Vout ) Vf) @ Ns + 571 VńmH + 571 mAńms (eq. 3) Lp V SS When projected over an Rsense of 0.1 W (for example), this becomes or 57 mV/ms. If we select 75% of the downslope as the required amount of ramp compensation, then we shall inject 43 mV/ms. Therefore, Rramp is simply equal to: + − 130ms delay Fault disable Drv & Softstart 1V max Figure 35. Block Diagram of Timer−Based Fault Detection http://onsemi.com 13 NCP1271 Skip Duty Cycle Skip peak current, %Icsskip, is the percentage of the maximum peak current at which the controller enters skip mode. Icsskip can be any value from 0 to 100% as defined by equation 5. However, the higher that %Icsskip is, the greater the drain current when skip is entered. This increases the risk of acoustic noise. Conversely, the lower that %Icsskip is the larger the percentage of energy is expended turning the switch on and off. Therefore it is important to adjust %Icsskip to the optimal level for a given application. Besides the timer−based fault detection, the NCP1271 also enters fault condition when VCC drops below VCC(off) (9.1 V typical). The device will again enter a double hiccup mode and try to restart the application. Operation in Standby Condition During standby operation, or when the output has a light load, the duty cycle on the controller can become very small. At this point, a significant portion of the power dissipation is related to the power MOSFET switching on and off. To reduce this power dissipation, the NCP1271 “skips” pulses when the FB level (i.e. duty cycle) drops too low. The level that this occurs at is completely adjustable by setting a resistor on pin 1. By discontinuing pulses, the output voltage slowly drops and the FB voltage rises. When the FB voltage rises above the Vskip level, the drive is turned back on. However, to minimize the risk of acoustic noise, when the drive turns back on the duty cycle of its pulses are also ramped up. This is similar to the soft start function, except the period of the Soft−Skip operation is only 300 ms instead of 4.0 ms for the soft start function. This feature produces a timing diagram shown in Figure 36. % Icsskip + Vskip · 100% 3V Skip Adjustment By default, when the Skip/latch Pin (Pin 1) is opened, the skip level is 1.2 V (Vskip = 1.2 V). This corresponds to a 40% Icsskip (%Icsskip = 1.2 V / 3.0 V 100% = 40%). Therefore, the controller will enter skip mode when the peak current is less than 40% of the maximum peak current. However, this level can be externally adjusted by placing a resistor Rskip between skip/latch pin (Pin 1) and Ground (Pin 4). The level will change according to equation 6. Vskip + Rskip Vskip FB (eq. 5) Iskip (eq. 6) To operate in skip cycle mode, Vskip must be between 0 V and 3.0 V. Therefore, Rskip must be within the levels given in Table 1. Soft Skip ID Figure 36. Soft−Skip Operation Table 1. Skip Resistor Rskip Range for Dmax = 80% and Iskip = 43 mA %Icsskip Vskip or Vpin1 Rskip 0% 0V 0W 12% 0.375 V 8.7 kW − 25% 0.75 V 17.4 kW − 40% 1.2 V 28 kW − 50% 1.5 V 34.8 kW − 100% 3.0 V 70 kW http://onsemi.com 14 Comment Never skips. Always skips. NCP1271 Recover from Standby In the event that a large load is encountered during skip cycle operation, the circuit automatically disables the normal Soft−Skip procedure and delivers maximum power to the load (Figure 37). This feature, the Transient Load Detector (TLD), is initiated anytime a skip event is exited and the FB pin is greater than 2.85 V, as would be the case for a sudden increase in output load. output voltage to be opened. The skip level Vskip is restored to the default 1.2 V. 3. When the voltage is between about 3.0 V and Vskip−reset, the Vskip level is above the normal operating range of the feedback pin. Therefore, the output does not switch. 4. When the voltage is between 0 V and 3.0 V, the Vskip is within the operating range of the feedback pin. Then the voltage on this pin sets the skip level as explained earlier. 300 ms max V pin1 10 V (max limit) Output is latched off here. load current V TLD Maximum current available when TLD level is hit Vskip V FB 8V (Vlatch ) Pin 1 considered to be opened. Vskip is reset to default level 1.2 V. 5.7 V (Vskip−reset ) Output always low (skipped) here. ID 3.0 V (always skip) Figure 37. Transient Response from Standby Adjustable Vskip range. External Latchoff Shutdown When the Skip/Latch input (Pin 1) is pulled higher than Vlatch (8.0 V typical), the drive output is latched off until VCC drops below VCC(reset) (4.0 Vtypical). If Vbulk stays above approximately 30 Vdc, then the HV FET ensure that VCC remains above VCC(latch) (5.8 Vtypical). Therefore, the controller is reset by unplugging the power supply from the wall and allowing Vbulk to discharge. Figure 38 illustrates the timing diagram of VCC in the latchoff condition. Startup current source is charging the VCC capacitor 0 V (no skip) Figure 39. NCP1271 Pin 1 Operating Regions The external latch feature allows the circuit designers to implement different kinds of latching protection. The NCP1271 applications note (AND8242/D) details several simple circuits to implement overtemperature protection (OTP) and overvoltage protection (OVP). In order to prevent unexpected latchoff due to noise, it is very important to put a noise decoupling capacitor near Pin 1 to increase the noise immunity. It is also recommended to always have a resistor from pin 1 to GND. This further reduces the risk of premature latchoff. Also note that if the additional latch−off circuitry has leakage, it will modify the skip adjust setup. Startup current source is off when VCC is 12.6 V 12.6 V External Non−Latched Shutdown Figure 40 illustrates the Feedback (pin 2) operation. An external non−latched shutdown can be easily implemented by simply pulling FB below the skip level. This is an inherent feature from the standby skip operation. Hence, it allows the designer to implement additional non−latched shutdown protection. The device can also be shutdown by pulling the VCC pin to GND (<190 mV). In addition to shutting off the output, this method also places the part into a low current consumption state. 5.8 V Startup current source turns on when VCC reaches 5.8 VCC Figure 38. Latchoff VCC Timing Diagram Figure 39 defines the different voltage regions of the Skip/latch Pin (Pin 1) operation. 1. When the voltage is above Vlatch (7.1 V min, 8.7 V max), the circuit is in latchoff and all drive pulses are disabled until VCC cycles below 4.0 V (typical). 2. When the voltage is between Vskip−reset (5.0 V min, 6.5 V max) and Vlatch, the pin is considered http://onsemi.com 15 NCP1271 V FB time of 30 ns and 20 ns with a 1.0 nF load. This allows the NCP1271 to drive a high−current power MOSFET directly for medium−high power application. Fault operation when staying in this region longer than 130 ms 3V Noise Decoupling Capacitors There are three pins in the NCP1271 that may need external decoupling capacitors. PWM operation V skip 1. Skip/Latch Pin (Pin 1) – If the voltage on this pin is above 8.0 V, then the circuit enters latchoff. Hence, a decoupling capacitor on this pin is essential for improved noise immunity. Additionally, a resistor should always be placed from this pin to GND to prevent noise from causing the pin 1 level to exceed the latchoff level. 2. Feedback Pin (Pin 2) – The FB pin is a high impedance point and is very easily polluted in a noisy environment. This could effect the circuit operation. 3. VCC Pin (Pin 6) – The circuit maintains normal operation when VCC is above VCC(off) (9.1 V typical). But, if VCC drops below VCC(off) because of switching noise, then the circuit can incorrectly recognize it as a fault condition. Hence, it is important to locate the VCC capacitor or an additional decoupling capacitor as close as possible to the device. Non−latched shutdown 0V Figure 40. NCP1271 Operation Threshold 1 8 2 OFF 3 6 4 5 NCP1271 opto coupler Figure 41. Non−Latchoff Shutdown Output Drive The output stage of the device is designed to directly drive a power MOSFET. It is capable of up to +500 mA and −800 mA peak drive currents and has a typical rise and fall http://onsemi.com 16 NCP1271 D1 − D4 1N5406 x 4 D10 MZP4746A (18V) R13 25 IC2 SFH615AA−X007 R11 15.8k R9 1.69k C12 0.15 uF IC4 TL431 R3 200 Flyback transformer : Cooper CTX22−17179 Lp = 180uH, leakage 2.5uH max np : ns : naux = 30 : 6 : 5 Hi−pot 3600Vac for 1 sec, primary to secondary Hi−pot 8500Vac for 1 sec, winding to core − R12 2.37k R8 0.2 / 1W R10 8.87k IC3 SFH615AA−X007 R7 511 Q1 SPP06N80C3 C4 100uF C14 100pF C13 100uF R6 10 C7 1.2 nF C6 1.2 nF R5 15.8k R2 10 19 V / 3 A D8 MBR3100 D7 MURS160 IC1 NCP1271A + C10 2200 uF C9 2200 uF D5 MMSZ914 D6 MRA4005T3 T1 E3506−A R1 100k / 2W C5 10 nF C3 82uF / 400V C2 0.1 uF Common Mode Choke 85 to 265 Vac C1 0.1 uF Fuse 2A C11 1nF/ 1000V D9 1N5358B (22V@50mA) Figure 42. 57 W Example Circuit Using NCP1271 Figure 42 shows a typical application circuit using the NCP1271. The standby power consumption of the circuit is 83 mW with 230 Vac input. The details of the application circuit are described in application note AND8242/D. The efficiency of the circuit at light load up to full load is shown in Figure 43. 95 EFFICIENCY (%) 90 120 Vac 85 230 Vac 80 75 70 65 60 0 10 20 30 40 50 Pout (W) Figure 43. Efficiency of the NCP1271 Demo Board at Nominal Line Voltages http://onsemi.com 17 60 NCP1271 ORDERING INFORMATION Frequency Package Shipping† NCP1271D65R2G 65kHz SOIC−7 (Pb−Free) 2500 Tape & Reel NCP1271D100R2G 100 kHz SOIC−7 (Pb−Free) 2500 Tape & Reel Device †For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specification Brochure, BRD8011/D. http://onsemi.com 18 NCP1271 PACKAGE DIMENSIONS SOIC−7 D SUFFIX CASE 751U−01 ISSUE C −A− 8 NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 2. CONTROLLING DIMENSION: MILLIMETER. 3. DIMENSION A AND B ARE DATUMS AND T IS A DATUM SURFACE. 4. DIMENSION A AND B DO NOT INCLUDE MOLD PROTRUSION. 5. MAXIMUM MOLD PROTRUSION 0.15 (0.006) PER SIDE. 5 0.25 (0.010) −B− S B M M 1 4 G C R X 45 _ J −T− SEATING PLANE H 0.25 (0.010) K M D 7 PL M T B S A DIM A B C D G H J K M N S MILLIMETERS MIN MAX 4.80 5.00 3.80 4.00 1.35 1.75 0.33 0.51 1.27 BSC 0.10 0.25 0.19 0.25 0.40 1.27 0_ 8_ 0.25 0.50 5.80 6.20 INCHES MIN MAX 0.189 0.197 0.150 0.157 0.053 0.069 0.013 0.020 0.050 BSC 0.004 0.010 0.007 0.010 0.016 0.050 0_ 8_ 0.010 0.020 0.228 0.244 S Soft−Skip is a trademark of Semiconductor Components Industries, LLC (SCILLC). The product described herein (NCP1271), may be covered by the following U.S. patents: 6,271,735, 6,362,067, 6,385,060, 6,597,221, 6,633,193. There may be other patents pending. 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 19 ON Semiconductor Website: www.onsemi.com Order Literature: http://www.onsemi.com/orderlit For additional information, please contact your local Sales Representative NCP1271/D