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| SG6859A -- Low Cost, Green-Mode PWM Controller for Flyback Converters March 2008 SG6859A Low-Cost, Green-Mode PWM Controller for Flyback Converters Features Green-Mode PWM Supports the "Blue Angel" Standard Low Start-up Current: 9A Low Operating Current: 3mA Leading-Edge Blanking Constant Output Power Limit Universal Input Built-in Synchronized Slope Compensation Current-Mode Operation Cycle-by-cycle Current Limiting Under-Voltage Lockout (UVLO) Programmable PWM Frequency with Frequency Hopping VDD Over-Voltage Protection (Auto Restart) Gate Output Voltage Clamped at 17V Low Cost Few External Components Required Small SOT-26 Package Description This highly integrated PWM controller provides several enhancements designed to meet the low standby-power needs of low-power SMPS. To minimize standby power consumption, the proprietary green-mode function provides off-time modulation to linearly decrease the switching frequency under light-load conditions. This green-mode function enables the power supply to meet even the strictest power conservation requirements. The BiCMOS fabrication process enables reducing the start-up current to 9A and the operating current to 3mA. To further improve power conservation, a large start-up resistance can be used. Built-in synchronized slope compensation ensures the stability of peak current mode control. Proprietary internal compensation provides a constant output power limit over a universal AC input range (90VAC to 264VAC). Pulse-by-pulse current limiting ensures safe operation during short-circuits. To protect the external power MOSFET from damage by supply over voltage, the SG6859A's output driver is clamped at 17V. SG6859A controllers can be used to improve the performance and reduce the production cost of power supplies. The best choice for replacing linear and RCC-mode power adapters, the SG6859A is available in 8-pin DIP and 6-pin SOT-26 packages. Applications General-purpose switching mode power supplies and flyback power converters, such as: Battery chargers for cellular phones, cordless phones, PDAs, digital cameras, and power tools Power adapters for ink jet printers, video game consoles, and portable audio players Open-frame SMPS for TV/DVD standby and auxiliary supplies, home appliances, and consumer electronics Replacements for linear transformers and RCC SMPS PC 5V standby power Ordering Information Part Number SG6859ATZ SG6859ADZ Operating Temperature Range -20C to +85C -20C to +85C Package SOT-26 DIP-8 Packing Method Tape & reel Tube All packages are lead free per JEDEC: J-STD-020B standard. (c) 2007 Fairchild Semiconductor Corporation SG6859A Rev. 1.0.0 www.fairchildsemi.com SG6859A -- Low-Cost, Green-Mode PWM Controller for Flyback Converters Application Diagram Figure 1. Typical Application Internal Block Diagram Figure 2. Functional Block Diagram (c) 2007 Fairchild Semiconductor Corporation SG6859A Rev. 1.0.0 www.fairchildsemi.com 2 SG6859A -- Low-Cost, Green-Mode PWM Controller for Flyback Converters Pin Configuration SOT-26 GND FB RI GATE VDD SENSE GATE VDD NC SENSE Figure 3. Pin Configurations DIP-8 GND FB NC RI Pin Definitions DIP Pin # 1 2 3 4 4 SOT Pin # 6 5 Name GATE VDD NC SENSE Description The totem-pole output driver for driving the power MOSFET. Power supply. No connection Current sense. This pin senses the voltage across a resistor. When the voltage reaches the internal threshold, PWM output is disabled. This activates overcurrent protection. This pin also provides current amplitude information for current-mode control. A resistor connected from the RI pin to ground generates a constant current source used to charge an internal capacitor and determine the switching frequency. Increasing the resistance reduces the amplitude of the current source and the switching frequency. A 95k resistor RI results in a 50A constant current II and a 70kHz switching frequency. No connection Feedback. The FB pin provides the output voltage regulation signal. It provides feedback to the internal PWM comparator, so that the PWM comparator can control the duty cycle. Ground. 5 3 RI 6 7 8 2 1 NC FB GND (c) 2007 Fairchild Semiconductor Corporation SG6859A Rev. 1.0.0 www.fairchildsemi.com 3 SG6859A -- Low-Cost, Green-Mode PWM Controller for Flyback Converters Absolute Maximum Ratings Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only. Symbol VVDD VFB VSENSE TJ JA TSTG TL ESD DC Supply Voltage (1, 2) Parameter Input Voltage to FB Pin Input Voltage to Sense Pin Operating Junction Temperature Thermal Resistance (Junction-to-Air) Storage Temperature Range Lead Temperature (Wave Soldering or IR, 10 Seconds) Electrostatic Discharge Capability, Human Body Model Electrostatic Discharge Capability, Machine Model SOT DIP Min. -0.3 -0.3 Max. 30 7.0 7.0 150 208.4 82.5 Unit V V V C C/W C/W C C kV V -55 150 260 3.5 200 Notes: 1. All voltage values, except differential voltages, are given with respect to GND pin. 2. Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. (c) 2007 Fairchild Semiconductor Corporation SG6859A Rev. 1.0.0 www.fairchildsemi.com 4 SG6859A -- Low-Cost, Green-Mode PWM Controller for Flyback Converters Electrical Characteristics Unless otherwise noted, VDD=15V and TA=25C. Symbol VDD Section VDD-OP VDD-ON VDD-OFF IDD-ST IDD-OP VDD-OVP Parameter Continuously Operation Voltage Turn-on Threshold Voltage Turn-off Threshold Voltage Startup Current Operating Supply Current VDD Over-voltage Protection Level VDD Low-threshold Voltage to Exit Green-off Mode Input Impedance FB Output High Voltage FB Open-loop Trigger Level Delay of FB Pin Open-loop Protection Green-Mode Entry FB Voltage Green-Mode Ending FB Voltage Green-Mode Modulation Slope Input Impedance Delay to Output Flat Threshold Voltage for Current Limit Valley Threshold Voltage for Current Limit Leading-Edge Blanking Time Duty Cycle of SAW Limit Center Frequency Hopping Range Conditions Min. Typ. Max. 22 Units V V V A mA V s V 15.5 8.5 VDD=VDD-ON - 0.1V VDD=15V, CL=1nF Auto Restart Auto Restart 24 16.5 9.5 9 3.0 25 125 VDD-OFF +1 5 17.5 10.5 15 3.5 26 tD-VDDOVP VDD Over-voltage Protection Debounce VDD-G OFF Feedback Input Section ZFB VFB-OPEN VFB-OL tD-OLP VFB-N VFB-G SG ZSENSE tPD VSTHFL VSTHVA tLEB DCYSAW k V 4.6 56 2.60 RI=95k 40 10 40 0.75 270 55 1 0.80 320 40 65 70 4.9 3.7 20 0 0.02 2.00 2 75 0.85 370 100 2.85 2.2 75 100 3.10 4.9 V ms V V Hz/mV k ns V V ns % 5 4.3 Current-Sense Section Oscillator Section FOSC THOP FOSC-G FDV FDT Frequency RI=95k RI=95k RI=95k VDD=13.5 to 22V TA=-20 to 85C kHz ms kHz % % Hopping Period Green-Mode Frequency Frequency Variation vs. VDD Deviation Frequency Variation vs. Temperature Deviation Maximum Duty Cycle Output Voltage Low Output Voltage High Rising Time Falling Time Output Clamp Voltage Output Section DCYMAX VGATE-L VGATE-H tr tf VGATECLAMP 62 VDD=15V, Io=20mA VDD=13.5V, Io=20mA VDD=15V, CL=1nF VDD=15V, CL=1nF VDD=22V 16 8 67 72 1.4 % V V ns ns 150 55 17 18 V (c) 2007 Fairchild Semiconductor Corporation SG6859A Rev. 1.0.0 www.fairchildsemi.com 5 SG6859A -- Low-Cost, Green-Mode PWM Controller for Flyback Converters Typical Performance Characteristics 17.0 13.0 16.8 12.0 16.6 VDD-OFF (V) -40 -25 -10 5 20 35 50 65 80 95 110 125 VDD-ON (V) 11.0 16.4 10.0 16.2 9.0 16.0 8.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 Temperature () Temperature () Figure 4. Turn-on Threshold Voltage (VDD-ON) vs. Temperature Figure 5. Turn-off Threshold Voltage (VDD-ON) vs. Temperature 3.0 3.5 2.5 3.3 2.0 IDD-OP (mA) -40 -25 -10 5 20 35 50 65 80 95 110 125 IDD-ST (A) 3.1 1.5 2.9 1.0 2.7 0.5 2.5 -40 -25 -10 5 20 35 50 65 80 95 110 125 Temperature () Temperature () Figure 6. Start-up Current (IDD-ST) vs. Temperature Figure 7. Operating Supply Current (IDD-OP) vs. Temperature 70.0 70.0 69.0 69.0 68.0 DCY (%) MAX -40 -25 -10 5 20 35 50 65 80 95 110 125 FOSC (KHz) 68.0 67.0 67.0 66.0 66.0 65.0 65.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 Temperature () Temperature () Figure 8. Center Frequency (FOSC) vs. Temperature Figure 9. Maximum Duty Cycle (DCYMAX) vs. Temperature (c) 2007 Fairchild Semiconductor Corporation SG6859A Rev. 1.0.0 www.fairchildsemi.com 6 SG6859A -- Low-Cost, Green-Mode PWM Controller for Flyback Converters Typical Performance Characteristics 3.2 3.0 3.0 2.8 VFB-N (V) 2.6 VFB-G (V) -40 -25 -10 5 20 35 50 65 80 95 110 125 2.8 2.6 2.4 2.4 2.2 2.2 2.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 Temperature () Temperature () Figure 10. Green-Mode Entry FB Voltage (VFB-N) vs. Temperature Figure 11. Green-Mode Ending FB Voltage (VFB-G) vs. Temperature 350.0 3.5 330.0 3.0 IDD-OP (mA) -40 -25 -10 5 20 35 50 65 80 95 110 125 tLEB (ns) 310.0 2.5 290.0 2.0 270.0 1.5 250.0 1.0 12 13 14 15 16 17 18 19 20 21 22 23 24 Temperature () VDD (V) Figure 12. Leading-Edge Blanking Time (tLEB) vs. Temperature Figure 13. Operating Supply Current vs. VDD Voltage (c) 2007 Fairchild Semiconductor Corporation SG6859A Rev. 1.0.0 www.fairchildsemi.com 7 SG6859A -- Low-Cost, Green-Mode PWM Controller for Flyback Converters Operation Description SG6859A devices integrate many useful designs into one controller for low-power, switch-mode power supplies. The following descriptions highlight some of the features of the SG6859A series. output GATE drive is turned off following a short propagation delay, tPD. This propagation delay introduces an additional current proportional to tPD*VIN/LP. The propagation delay is nearly constant, regardless of the input line voltage VIN. Higher input line voltages result in larger additional currents. At high input line voltages, the output power limit is higher than at low input line voltages. To compensate for this output power limit variation across a wide AC input range, the threshold voltage is adjusted by adding a positive ramp. This ramp signal rises from 0.8V to 1V, then flattens out at 1V. A smaller threshold voltage forces the output GATE drive to terminate earlier, which reduces the total PWM turn-on time and makes the output power equal to that of low line input. This proprietary internal compensation ensures a constant output power limit for a wide AC input voltage range (90VAC to 264VAC). Start-up Current The start-up current is only 9A. Low start-up current allows a start-up resistor with high resistance and lowwattage to supply the start-up power for the controller. A 1.5M, 0.25W, start-up resistor and a 10F/25V VDD hold-up capacitor are sufficient for an AC-to-DC power adapter with a wide input range (100VAC to 240VAC). Operating Current The operating current has been reduced to 3mA. The low operating current results in higher efficiency and reduces the VDD hold-up capacitance requirement. Under-Voltage Lockout (UVLO) The turn-on and turn-off thresholds are fixed internally at 16.5V and 9.5V. During start-up, the hold-up capacitor must be charged to 16.5V through the start-up resistor to enable the SG6859A. The hold-up capacitor continues to supply VDD until power can be delivered from the auxiliary winding of the main transformer. VDD must not drop below 9.5V during this start-up process. This UVLO hysteresis window ensures that hold-up capacitor is adequate to supply VDD during start-up. Green-Mode Operation The proprietary green-mode function provides off-time modulation to linearly decrease the switching frequency under light-load conditions. On-time is limited to provide stronger protection against brownouts and other abnormal conditions. The feedback current, which is sampled from the voltage feedback loop, is taken as the reference. Once the feedback current exceeds the threshold current, the switching frequency starts to decrease. This green-mode function dramatically reduces power consumption under light-load and zeroload conditions. Power supplies using the SG6859A can meet even the strictest regulations regarding standby power consumption. Gate Output The BiCMOS output stage is a fast totem pole gate driver. Cross conduction has been avoided to minimize heat dissipation, increase efficiency, and enhance reliability. The output driver is clamped by an internal 17V Zener diode to protect power MOSFET transistors against undesired over-voltage gate signals. Oscillator Operation A resistor connected from the RI pin to ground generates a constant current source used to charge an internal capacitor. The charge time determines the internal clock speed and the switching frequency. Increasing the resistance reduces the amplitude of the input current and the switching frequency. A 95k RI resistor results in a 50A constant current II and a 70kHz switching frequency. The relationship between RI and the switching frequency is: fPWM = 6650 (kHz) RI(k) Built-in Slope Compensation The sensed voltage across the current-sense resistor is used for current-mode control and pulse-by-pulse current limiting. Built-in slope compensation improves stability and prevents sub-harmonic oscillations due to peak-current mode control. The SG6859A has a synchronized, positively-sloped ramp built-in at each switching cycle. The slope of the ramp is: 0.36 x Duty Duty(max.) (2) (1) Leading-Edge Blanking Each time the power MOSFET is switched on, a turn-on spike occurs at the sense-resistor. To avoid premature termination of the switching pulse, a 320ns leadingedge blanking time is built in. Conventional RC filtering can be omitted. During this blanking period, the currentlimit comparator is disabled and cannot switch off the gate driver. Noise Immunity Noise from the current sense or the control signal can cause significant pulse-width jitter, particularly in continuous-conduction mode (CCM). While slope compensation helps alleviate these problems, further precautions should still be taken. Good placement and layout practices should be followed. Avoiding long PCB traces and component leads, locating compensation and filter components near the SG6859A, and increasing power MOS gate resistance improve performance. www.fairchildsemi.com 8 Constant Output Power Limit When the SENSE voltage across the sense resistor, RS, reaches the threshold voltage (around 1V), the (c) 2007 Fairchild Semiconductor Corporation SG6859A Rev. 1.0.0 SG6859A -- Low-Cost, Green-Mode PWM Controller for Flyback Converters Applications Information F1 1 BD1 C3 R1 CX1 2 4 C1 C2 R5 3 R2 1 N R4 10 9 D1 2 2 8 5 Q1 3 7 3,4 2 GND R10 C7 C8 D5 C9 1 T1 1,2 2 D4 1 1 L2 2 VO R3 1 L1 2 L U1 1 2 3 C6 R9 GND GATE FB RI VDD SENSE 6 5 4 R7 1 R15 C11 R6 R8 D2 1 2 R11 C4 4 1 R13 U2 R14 3 2 3 CY1 C10 U3 1 R12 2 Figure 14. Reference Circuit BOM Reference BD1 CX1 (Optional) CY1 (Optional) C1 C2 C3 C4 C6 C7 (Optional) C8 C9 C10 C11 D1 D2 D4 D5 (Optional) F1 L1 Component BD 1A/500V XC 0.1F YC 102P/400V (Y1) CC 103P/500V EC 10F/400V 105C CC 102P/500V EC 10F/50V CC 472P 0805 CC 102P/100V 1206 EC 470F/10V 105C EC 220F/10V 105C CC 222P 0805 N.C. Diode FRI07 Diode FR102 Diode SB360 ZD 6.8V 0.5W R 1/0.5W 20mH 6*8mm Reference L2 Q1 R1,R2 R3,R4 R5 R6 R7 R8 R9 R10 (Optional) R11 R12 R13 R14 R15 T1 U1 U2 U3 Component 10H 6mm MOSFET 1A/600V R 750K 1206 R 47K 1206 R 47 1206 R 4.7 1206 R 100 0805 R 10 1206 R 100K 0805 R 10 1206 R 100 1/8W R 33K 0805 R 33K 1/8W R 4.7K 0805 R 0 0805 EE-16 IC SG6859A PC817 TL431 (c) 2007 Fairchild Semiconductor Corporation SG6859A Rev. 1.0.0 www.fairchildsemi.com 9 SG6859A -- Low-Cost, Green-Mode PWM Controller for Flyback Converters Physical Dimensions D 8 5 X E1 E eB 1 4 A1 A2 L b1 b e Figure 15. 8-Pin Dip-8 Package Dimensions Symbol A A1 A2 b b1 D E E1 e L eB 2.921 8.509 0 6.223 9.017 0.381 3.175 3.302 1.524 0.457 9.271 7.620 6.350 2.540 3.302 9.017 7 3.810 9.525 15 0.115 0.335 0 6.477 0.245 10.160 0.355 3.429 Millimeters Min. A Typ. Max. 5.334 Inches Min. 0.015 0.125 Typ. Max. 0.210 0.130 0.060 0.018 0.365 0.300 0.250 0.100 0.130 0.355 7 0.135 0.400 0.255 0.150 0.375 15 (c) 2007 Fairchild Semiconductor Corporation SG6859A Rev. 1.0.0 www.fairchildsemi.com 10 SG6859A -- Low-Cost, Green-Mode PWM Controller for Flyback Converters Physical Dimensions (Continued) D b 6 4 Detail A E1 E 1 e1 e 3 c 1 R A2 A L A1 L1 1 Detail A Figure 16. 6-Pin SOT-26 Package Dimensions Symbol A A1 A2 b c D E E1 e e1 L L1 L2 R R1 1 Millimeters Min. Typ. Max. 1.45 0.15 Inches Min. 0.90 0.30 0.08 1.15 1.30 0.50 0.22 0.036 0.011 0.003 2.90 2.80 1.60 0.95 1.90 0.30 0.45 0.60 0.25 0.10 0.10 0 5 4 10 0.25 8 15 0.004 0.004 0 5 0.60 0.020 (c) 2007 Fairchild Semiconductor Corporation SG6859A Rev. 1.0.0 11 L2 R 1 Typ. Max. 0.057 0.006 0.045 0.051 0.020 0.009 0.114 0.110 0.063 0.037 0.075 0.018 0.024 0.010 0.010 4 10 8 15 0.024 www.fairchildsemi.com SG6859A -- Low-Cost, Green-Mode PWM Controller for Flyback Converters (c) 2007 Fairchild Semiconductor Corporation SG6859A Rev. 1.0.0 www.fairchildsemi.com 12 |
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