Product Specification SG6848 Low Cost Green-Mode PWM Controller for Flyback Converters FEATURES DESCRIPTION Green-Mode PWM Supports the “Blue Angel” Standard Low Start-up Current (5uA) Low Operating Current (2mA) 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 Gate Output Voltage Clamped at 15V Low Cost Few External Components Required Small SOT-26 Package This highly-integrated PWM controller provides several special 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 easily meet even the strictest power conservation requirements. The BiCMOS fabrication process enables reducing the start-up current to 5uA, and the operating current to 2mA. 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 even during short-circuits. 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 other auxiliary supplies, home appliances, and consumer electronics Replacements for linear transformers and RCC SMPS PC 5V standby power. TYPICAL APPLICATION To protect the external power MOSFET from being damaged by supply over voltage, the SG6848’s output driver is clamped at 15V. SG6848 controllers can be used to improve the performance and reduce the production cost of power supplies. The SG6848 is the best choice for replacing linear and RCC-mode power adapters. It is available in 8-pin DIP and 6-pin SOT-26 packages. From bridge rectifier 120~ 380VDC From auxiliary winding RIN 1.5M VDD CIN 10u R7 100 FB OUTPUT C6 472p SG6848 SENSE R9 95k RI RS 4.7 GND © System General Corp. Version 1.2(IRO33.0010.B0) -1- www.sg.com.tw May.06, 2003 Product Specification SG6848 Low Cost Green-Mode PWM Controller for Flyback Converters MARKING DIAGRAMS PIN CONFIGURATION SOT-26 M: Mask Version Y: Year; WW: Work Week MAYWW GND 1 6 GATE FB 2 5 VDD RI 3 4 SENSE 1 8 DIP-8 XXXXXXX: Wafer Lot YY: Year; WW: Week V: Assembly Location SG6848D XXXXXXXYYWWV 1 GATE 1 8 GND VDD 2 7 FB NC 3 6 NC SENSE 4 5 RI ORDERING INFORMATION Part Number PWM Frequency Package SG6848T 70kHz 6-Pin SOT-26 SG6848D 70kHz 8-pin DIP-8 PIN DESCRIPTIONS Name Pin No. DIP-8 / (SOT-26) Type Function The totem-pole output driver for driving the power MOSFET. GATE 1 / (6) Driver Output VDD 2 / (5) Supply NC 3 SENSE 4 / (4) Power supply. NC pin. Current sense. This pin senses the voltage across a resistor. When the voltage reaches Analog Input the internal threshold, PWM output is disabled. This activates over-current protection. This pin also provides current amplitude information for current-mode control. A resistor connected from the RI pin to ground will generate a constant current source for RI 5 / (3) Analog Input/Output the SG6848. This current is used to charge an internal capacitor, to determine the switching frequency. Increasing the resistance will reduce the amplitude of the current source and reduce the switching frequency. A 95kΩ resistor Ri results in a 50uA constant current Ii and a 70kHz switching frequency. NC 6 NC pin. FB 7 / (2) Analog Input GND 8 / (1) Supply © System General Corp. Version 1.2(IRO33.0010.B0) 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. -2- www.sg.com.tw May.06, 2003 Product Specification SG6848 Low Cost Green-Mode PWM Controller for Flyback Converters BLOCK DIAGRAM GND RI 8 (1) 5 (3) VDD ON/OFF Driver Internal Bias VDD 2 (5) OSC 1 (6) GATE 4 (4) SENSE 7 (2) FB S Q R OCP Comp Vlimit ramp + Blanking Circuit Slope Compensation _ UVLO 4.8V PWM Comp 16.3V/11.7V Green Mode Controller ABSOLUTE MAXIMUM RATINGS Symbol Parameter Value Unit VDD DC Supply Voltage * 25 V Zener Clamp 26 V Zener Current 10 mA VFB Input Voltage to FB Pin -0.3 to 6 V V VSense Input Voltage to Sense Pin -0.3 to 6V V Pd Power Dissipation 300 mW TJ Operating Junction Temperature 150 ℃ RθJA Thermal Resistance (Junction to Air) SOT-26 208.4 °C/W DIP-8 82.5 °C/W Tstg Storage Temperature Range -55 to +150 ℃ TL Lead Temperature (Soldering) 20 sec SOT-26 220 10 sec DIP-8 260 °C ESD Capability, HBM Model 3.0 kV ESD Capability, Model 300 V * All voltage values, except differential voltages, are given with respect to the network ground terminal. © System General Corp. Version 1.2(IRO33.0010.B0) -3- www.sg.com.tw May.06, 2003 Product Specification SG6848 Low Cost Green-Mode PWM Controller for Flyback Converters RECOMMENDED OPERATING CONDITIONS Symbol Parameter Value Unit VDD DC Supply Voltage ≦20 V Ta Operating Ambient Temperature -30 to +85 ℃ ELECTRICAL CHARACTERISTICS (TA = 25°°C, VDD=15V) Feedback Input Section Symbol Parameter Typ. Max. Unit Ioz Zero Duty Cycle Input Current Test Condition Min. 1.3 2.0 mA Vop Open Loop Voltage 4.5 V Current Sense Section Symbol Parameter Zcs Input Impedance Test Condition Min. Typ. TPD Delay to Output 150 VTH,FLT Current Limit Flatten Threshold Voltage 1.0 VTH,VALLEY Current Limit Valley Threshold Voltage Max. 10 0.80 Unit kΩ 0.85 200 nsec V 0.90 V Oscillator Section Symbol Parameter Test Condition Min. Typ. Max. Unit Fosc Frequency RI=95kΩ 65 70 75 kHz Fosc-green Green-Mode Frequency RI=95kΩ 13 15 kHz Ig Green-Mode FB Input Current In Green-Mode Start Threshold FB Input Current In = 0.3mA for a Maximum Duty Cycle 1.16 mA 1 mA Sg Green-Mode Modulation Slope RI=95kΩ 300 Fdv Frequency Variation versus VDD Deviation VDD=12 to 20V 0.02 Fdt Frequency Variation versus Temp. Deviation TA=-30 to 85 ℃ Hz/uA 2 % 2 % PWM Section Symbol Parameter DC (MAX) DC (MIN) Bnk Leading-Edge Blanking Time Test Condition Min. Typ. Max. Unit Maximum Duty Cycle 70 75 80 % Minimum Duty Cycle - 1 2 % 250 nsec Output Section Symbol Parameter Test Condition Vol Output Voltage Low VDD=15V, Io=20mA Voh Output Voltage High VDD=15V, Io=20mA tr Rising Time VDD=15V, CL=1nF tf Falling Time VCLAMP Output Clamp Voltage © System General Corp. Version 1.2(IRO33.0010.B0) Max. Unit 1.5 V 50 200 nsec VDD=15V, CL=1nF 30 150 nsec VDD=20V 15 17 V -4- Min. Typ. 8 V www.sg.com.tw May.06, 2003 Product Specification SG6848 Low Cost Green-Mode PWM Controller for Flyback Converters Under Voltage Lockout Section Symbol Parameter Test Condition Min. Typ. Max. Unit VTH(ON) Start Threshold Voltage TA=25°C 15.3 16.3 17.3 V VDD(min) Min. Operating Voltage TA=25°C 10.9 11.7 12.5 V Min. Total Standby Current Section Symbol Parameter Test Condition Typ. Max. Unit IDD ST Start-up Current VDD=15V 5 30 uA IDD OP Operating Supply Current VDD=15V 2 5 mA © System General Corp. Version 1.2(IRO33.0010.B0) -5- www.sg.com.tw May.06, 2003 Product Specification SG6848 Low Cost Green-Mode PWM Controller for Flyback Converters TYPICAL CHARACTERISTICS Min. Operating Voltage (V DD (min)) vs Temperature Start-up Threshold Voltage (V TH(ON)) vs Tem perature 12.2 17.0 12.0 11.8 VDD (min) (V) VTH(ON) (V) 16.5 16.0 15.5 11.6 11.4 11.2 11.0 15.0 10.8 14.5 10.6 -40 -25 -10 5 20 35 50 65 80 95 110 125 -40 -25 -10 5 TEMPERATURE (℃ ℃) 20 35 50 65 80 95 110 125 TEMPERATURE ( ℃ ) PWM Oscillator Frequency (FOSC) vs Tem perature Start-up Crrent (IDD ST) vs Tem perature 30 74.0 25 72.5 FOSC (KHz) IDD ST (uA) 20 15 10 71.0 69.5 68.0 5 66.5 0 65.0 -40 -25 -10 5 20 35 50 65 80 95 110 125 -40 -25 -10 5 TEMPERATURE ( ℃ ) 20 35 50 65 80 95 110 125 TEMPERATURE (℃ ℃) Frequency in green m ode (FOSC-green) vs Tem perature Max. Duty Cycle (DC(MAX)) vs Tem perature 80 15 79 78 13 DC (MAX) (%) FOSC-green (KHz) 14 12 11 77 76 75 74 73 10 72 9 71 70 8 -40 -25 -10 5 20 35 50 65 80 95 110 -40 125 TEMPERATURE ( ℃ ) © System General Corp. Version 1.2(IRO33.0010.B0) -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE ( ℃ ) -6- www.sg.com.tw May.06, 2003 Product Specification Low Cost Green-Mode PWM Controller for Flyback Converters SG6848 PWM Oscillator Frequency (FOSC) vs. FB 80 70 F OSC (KHz) 60 50 40 30 20 10 0 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 FB (mA) © System General Corp. Version 1.2(IRO33.0010.B0) -7- www.sg.com.tw May.06, 2003 Product Specification SG6848 Low Cost Green-Mode PWM Controller for Flyback Converters OPERATION DESCRIPTION SG6848 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 SG6848 series. switching frequency. Increasing the resistance will reduce the amplitude of the input current and reduce the switching frequency. A 95kΩ resistor Ri results in a 50uA constant current Ii and a 70kHz switching frequency. The relationship between Ri and the switching frequency is: fPWM = Start-up Current The start-up current is only 5uA. Low start-up current allows a start-up resistor with a high resistance and a low-wattage to supply the start-up power for the controller. A 1.5 MΩ, 0.25W, start-up resistor and a 10uF/25V VDD hold-up capacitor would be 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 2mA. The low operating current results in higher efficiency and reduces the Vcc hold-up capacitance requirement. 6650 R I (k Ω ) (kHz ) The range of the oscillation frequency is designed to be within 50kHz ~ 100kHz. Leading-Edge Blanking Each time the power MOSFET is switched on, a turn-on spike will inevitably occur at the sense-resistor. To avoid premature termination of the switching pulse, a 250 nsec leading-edge blanking time is built in. Conventional RC filtering can therefore be omitted. During this blanking period, the current-limit comparator is disabled and it cannot switch off the gate driver. Constant Output Power Limit 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 zero-load conditions. Power supplies using the SG6848 can easily meet even the strictest regulations regarding standby power consumption. Oscillator Operation A resistor connected from the RI pin to ground will generate a constant current source for the SG6848. This current is used to charge an internal capacitor. The charge-time determines the internal clock speed and the © System General Corp. Version 1.2(IRO33.0010.B0) When the SENSE voltage across the sense resistor Rs reaches the threshold voltage (around 1.0V), the output GATE drive will be turned off following a short propagation delay tD. This propagation delay will introduce an additional current proportional to tD*Vin/Lp. The propagation delay is nearly constant regardless of the input line voltage VIN. Higher input line voltages will result in larger additional currents. At high input line voltages, the output power limit will be 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 0.85V to 1.0V, and then flattens out at 1.0V. A smaller threshold voltage forces the output GATE drive to terminate earlier. This 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). -8- www.sg.com.tw May.06, 2003 Product Specification Low Cost Green-Mode PWM Controller for Flyback Converters SG6848 Under Voltage Lockout (UVLO) The turn-on and turn-off thresholds of the SG6848 are fixed internally at 16.3V/11.7V. During start-up, the hold-up capacitor must be charged to 16.3V through the start-up resistor, so that the SG6848 will be enabled. The hold-up capacitor will continue to supply VDD until power can be delivered from the auxiliary winding of the main transformer. VDD must not drop below 11.7V during this start-up process. This UVLO hysteresis window ensures that hold-up capacitor will be adequate to supply VDD during start-up. 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 will improve stability and prevent sub-harmonic oscillations due to peak-current mode control. The SG6848 has a synchronized, positively-sloped ramp built-in at each switching cycle. The slope of the ramp is: 0.33 × Duty Duty(max) Gate Output The SG6848 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 15V Zener diode in order to protect power MOSFET transistors against undesired over-voltage gate signals. © System General Corp. Version 1.2(IRO33.0010.B0) Noise Immunity Noise from the current sense or the control signal can cause significant pulse width jitter, particularly in continuous-conduction mode. 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 SG6848, and increasing the power MOS gate resistance is advised. -9- www.sg.com.tw May.06, 2003 Product Specification SG6848 Low Cost Green-Mode PWM Controller for Flyback Converters REFERENCE CIRCUIT Circuit F1 L1 1 CX1 2 BD1 2 - + 4 + C1 R1 C2 C3 R3 R5 R4 D4 T1 3 N R2 3 1 L2 1 VO 2 R10 8 5 GATE FB VDD RI SENSE 6 + D5 + C9 Q1 1 2 GND R7 C7 C8 5 3 2 C6 2 9 D1 22 U1 1 1,2 1 10 1 1 L 7 4 GND 3,4 R6 R9 R8 + D2 1 2 R11 C4 U2 4 R13 1 2 C10 3 3 R14 U3 CY1 1 2 R12 BOM Reference Component Reference Component BD1 BD 1A/500V L2 10uH 6mm CX1 (Optional) YC 472P/400V (Y1) Q1 MOSFET 1A/600V CY1 (Optional) YC 102P/400V (Y1) R1,R2 R 750KΩ 1206 R4,R3 R 47KΩ 1206 C2 EC 10uF/400V 105℃ C1 CC 103P/500V R5 R 47Ω 1206 C3 CC 1000P/500V R6 R 4.7Ω 1206 C4 EC 10u/50V R7 R 100Ω 0805 C6 CC 472P 0805 R8 C7 (Optional) CC 102P/100V 1206 R10 R 10Ω 1206 (Optional) R 10Ω 1206 C8 EC 470u/10V 105℃ R9 R 100KΩ 0805 C9 EC 220u/10V 105℃ R11 R 100Ω 1/8W C10 CC 222P 0805 R12 R 33KΩ 0805 D1 Diode FRI07 R13 R 33KΩ 1/8W D2 Diode FR102 R14 R 4.7KΩ 0805 Diode SB360 T1 EE-16 U1 IC SG6848 (Green PWM IC) D4 D5 (Optional) ZD 6.8V 0.5W F1 R 1Ω/0.5W U2 PC817 L1 20mH 6*8mm U3 TL431 © System General Corp. Version 1.2(IRO33.0010.B0) - 10 - www.sg.com.tw May.06, 2003 Product Specification SG6848 Low Cost Green-Mode PWM Controller for Flyback Converters PACKAGE INFORMATION 8 PINS -- DIP (D) D Θ° 5 E1 8 B A A2 4 A1 1 e E L b1 e b Dimensions Symbol Millimeters Min. Typ. A Inches Min. Max. Typ. 5.334 A1 0.381 A2 3.175 0.210 0.015 3.302 3.429 0.125 0.130 b 1.524 0.060 b1 0.457 0.018 D 9.017 E E1 9.271 10.160 0.355 7.620 6.223 e Max. 6.350 0.365 0.135 0.400 0.300 6.477 0.245 2.540 0.250 0.255 0.100 L 2.921 3.302 3.810 0.115 0.130 0.150 eB 8.509 9.017 9.525 0.335 0.355 0.375 θ˚ 0˚ 7˚ 15˚ 0˚ 7˚ 15˚ © System General Corp. Version 1.2(IRO33.0010.B0) - 11 - www.sg.com.tw May.06, 2003 Product Specification SG6848 Low Cost Green-Mode PWM Controller for Flyback Converters SOT-26 (S) D Detail A b 4 E E1 6 1 e c 3 1 R R θ A A2 1 L2 e1 L A1 θ L1 1 θ Detail A Dimensions Symbol Millimeters Min. Typ. Inches Min. Max. Typ. Max. A 1.45 0.057 A1 0.15 0.006 A2 0.90 b c 1.30 0.036 0.30 0.50 0.011 0.08 0.22 0.003 D 1.15 2.90 0.045 0.020 0.009 0.114 E 2.80 0.110 E1 1.60 0.063 e 0.95 0.037 e1 1.90 0.075 L 0.30 0.45 L1 0.60 L2 0.25 0.051 0.60 0.020 0.018 0.024 0.024 0.010 R 0.10 R1 0.10 0.25 0.004 θ˚ 0˚ 4˚ 8˚ 0˚ 4˚ 8˚ θ1˚ 5˚ 10˚ 15˚ 5˚ 10˚ 15˚ © System General Corp. Version 1.2(IRO33.0010.B0) 0.004 - 12 - 0.010 www.sg.com.tw May.06, 2003 Product Specification Low Cost Green-Mode PWM Controller for Flyback Converters SG6848 DISCLAIMERS LIFE SUPPORT System General’s products are not designed to be used as components in devices intended to support or sustain human life. Use of System General’s products in components intended for surgical implant into the body, or other applications in which failure of System General’s products could create a situation where personal death or injury may occur, is not authorized without the express written approval of System General’s Chief Executive Officer. System General will not be held liable for any damages or claims resulting from the use of its products in medical applications. MILITARY System General's products are not designed for use in military applications. Use of System General’s products in military applications is not authorized without the express written approval of System General’s Chief Executive Officer. System General will not be held liable for any damages or claims resulting from the use of its products in military applications. RIGHT TO MAKE CHANGES System General reserves the right to change this document and/or this product without notice. Customers are advised to consult their System General sales representative before ordering. © System General Corp. Version 1.2(IRO33.0010.B0) - 13 - www.sg.com.tw May.06, 2003