SG6741A Highly Integrated Green-Mode PWM Controller

Transcription

1 SG674A Highly Integrated Green-Mode PWM Controller Features High-Voltage Startup Low Operating Current: 4mA Linearly Decreasing PWM Frequency to 8kHz Frequency Hopping to Reduce EMI Emissions Peak-Current-Mode Control Cycle-by-Cycle Current Limiting Leading-Edge Blanking (LEB) Synchronized Slope Compensation GATE Output Maximum Voltage Clamp: 8V V DD Over-Voltage Protection (Auto Restart) V DD Under-Voltage Lockout (UVLO) Internal Open-Loop Protection Constant Power Limit (Full AC Input Range) Applications General-purpose switch-mode power supplies and flyback power converters, including: Power Adapters Open-Frame SMPS Description October 008 The highly integrated SG674A series of PWM controllers provides several features to enhance the performance of flyback converters. To minimize standby power consumption, a proprietary green-mode function provides off-time modulation to linearly decrease the switching frequency at light-load conditions. To avoid acoustic-noise problems, the minimum PWM frequency is set above 8KHz. This green-mode function enables the power supply to meet international power conservation requirements. With the internal high-voltage startup circuitry, the power loss due to bleeding resistors is eliminated. To further reduce power consumption, SG674A is manufactured using the BiCMOS process, which allows an operating current of only 4mA. SG674A integrates a frequency-hopping function internally to reduce EMI emission of a power supply with minimum line filters. A built-in synchronized slope compensation achieves stable peak-current-mode control. The proprietary internal line compensation ensures constant output power limit over a wide AC input voltages, from 90V AC to 64 V AC. SG674A provides many protection functions. In addition to cycle-by-cycle current limiting, the internal open-loop protection circuit ensures safety when an open-loop or output short-circuit failure occurs. PWM output is disabled until V DD drops below the UVLO lower limit, when the controller starts up again. As long as V DD exceeds ~6V, the internal OVP circuit is triggered. SG674A is available in an 8-pin SOP package. SG674A Highly Integrated Green-Mode PWM Controller Ordering Information Part Number Operating Temperature Range Package Eco Status Packing Method SG674ASZ -40 to +05 C 8-Lead Small Outline Package (SOP) Green Tape & Reel SG674ASY -40 to +05 C 8-Lead Small Outline Package (SOP) Green Tape & Reel For Fairchild s definition of green Eco Status, please visit: Fairchild Semiconductor Corporation SG674A Rev..0.

2 Application Diagram Block Diagram Figure. Typical Application SG674A Highly Integrated Green-Mode PWM Controller Figure. Block Diagram 008 Fairchild Semiconductor Corporation SG674A Rev..0.

3 Marking Information marking for SG674ASZ marking for SG674ASY Pin Configuration SG674ATP XXXXXXXXYWWV ZXYTT 674A TPM GND FB NC T: S = SOP P: Z =Lead Free Null=regular package XXXXXXXX: Wafer Lot Y: Year; WW: Week V: Assembly Location F: Fairchild logo Z: Plant code X: digit year code Y: digit week code TT: digits die run code T: Package type (S = SOP) P: Y=Green package M: Manufacture flow code Figure 3. Top Mark GATE VDD SENSE SG674A Highly Integrated Green-Mode PWM Controller HV RI Figure 4. Pin Configuration Pin Definitions Pin # Name Description GND Ground. FB Feedback. The signal from the external compensation circuit is fed into this pin. The PWM duty cycle is determined in response to the signal on this pin and the current-sense signal on SENSE pin. 3 NC No Connection. 4 HV Startup Input. For startup, this pin is pulled HIGH to the line input or bulk capacitor via resistors. 5 RI 6 SENSE Reference Setting. A resistor connected from the RI pin to GND pin provides a constant current source, which determines the center PWM frequency. Increasing the resistance reduces PWM frequency. Using a 6KΩ resistor for R I results in a 65kHz center PWM frequency. Current Sense. The sensed voltage is used for peak-current-mode control and cycle-by-cycle current limiting. 7 VDD Power Supply. The internal protection circuit disables PWM output as long as V DD exceeds the OVP trigger point. 8 GATE Driver Output. Totem-pole output driver. Soft driving waveform is implemented for improved EMI. 008 Fairchild Semiconductor Corporation SG674A Rev..0. 3

4 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. All voltage values, except differential voltages, are given with respect to the ground pin. Symbol Parameter Min. Max. Unit V VDD DC Supply Voltage (, ) 30 V V FB FB Pin Input Voltage V V SENSE SENSE Pin Input Voltage V V RI RI Pin Input Voltage V V HV HV Pin Input Voltage 500 V P D Power Dissipation (T A<50 C) 400 mw Θ JA Thermal Resistance (Junction-to-Air) 4 C/W T J Operating Junction Temperature C T STG Storage Temperature Range C T L Lead Temperature (Wave Soldering or IR, 0 Seconds) +60 C ESD Electrostatic Discharge Capability, Human Body Model, JESD-A4 All Pins Except HV Pin 4 kv Electrostatic Discharge Capability, Machine Model, JESD-A5 All Pins Except HV Pin 00 V Notes:. All voltage values, except differential voltages, are given with respect to the network ground terminal.. Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. SG674A Highly Integrated Green-Mode PWM Controller 008 Fairchild Semiconductor Corporation SG674A Rev..0. 4

5 Electrical Characteristics V DD=5V; T A=5C, unless otherwise noted. Symbol Parameter Conditions Min. Typ. Max. Units V DD Section V DD-OP Continuously Operating Voltage V V DD-ON Start Threshold Voltage V V DD-OFF Minimum Operating Voltage V I DD-ST Startup Current V DD-ON 0.6V 30 µa I DD-OP Operating Supply Current V DD=5V, GATE Open 4 5 ma I DD-OLP Internal Sink Current V DD-OLP +0.V µa V DD-OLP I DD-OLP off Voltage V V DD-OVP V DD Over-Voltage Protection Auto Restart V t D-VDDOVP V DD Over-Voltage Protection Debounce Time HV Electrical Characteristics I HV I HV-LC Oscillator Section f OSC Supply Current Drawn from HV Pin Leakage Current After Startup Frequency in Nominal Mode Auto Restart µs V AC=90V, (V DC=0V) V DD=0µF HV=500V, V DD=V DD- OFF+V ma 0 µa Center Frequency Hopping Range ±3.7 ±4. ±4.7 t HOP Hopping Period 4.4 ms f OSC-G Green-Mode Frequency 6 8 khz khz SG674A Highly Integrated Green-Mode PWM Controller f DV f DT Feedback Input Section A V Frequency Variation vs. V DD Deviation Frequency Variation vs. Temperature Deviation Input Voltage to Current-Sense Attenuation V DD=V to V 5 % T A=-0 to 85 C 5 % /3.75 /3.0 /.75 V/V Z FB Input Impedance 4 7 kω V FB-OPEN FB Output High Voltage FB Pin Open 5.5 V V FB-OLP FB Open-loop Trigger Level V t D-OLP The Delay Time of FB Pin Open- Loop Protection R I=6kΩ ms V FB-N Green-Mode Entry FB Voltage.9..3 V V FB-G Green-Mode Ending FB Voltage V FB-N V FB-ZDC Zero Duty-Cycle Input Voltage V Continued on following page V 008 Fairchild Semiconductor Corporation SG674A Rev..0. 5

6 Electrical Characteristics (Continued) V DD=5V; T A=5C, unless otherwise noted. PWM Frequency f OSC f OSC - V FB-ZDC V FB-G VFB-N Figure 5. PWM Frequency Symbol Parameter Conditions Min. Typ. Max. Units Current Sense Section Z SENSE Input Impedance KΩ V STHFL Current Limit Flatten Threshold Voltage V V STHVA Current Limit Valley Threshold Voltage V STHFL V STHVA V t PD Delay to Output ns t LEB Leading-Edge Blanking Time ns Gate Section DCY MAX Maximum Duty Cycle % V GATE-L Gate Low Voltage V DD=5V, I O=50mA.5 V V GATE-H Gate High Voltage V DD=.5V, I O=-50mA 8 V tr Gate Rising Time V DD=5V, C L=nF ns tf Gate Falling Time V DD=5V, C L=nF ns I GATE-SOURCE Gate Source Current V DD=5V, GATE=6V 50 ma V GATE-CLAMP Gate Output Clamping Voltage V DD=V 8 V DCY MAX Maximum Duty Cycle % VFB SG674A Highly Integrated Green-Mode PWM Controller 008 Fairchild Semiconductor Corporation SG674A Rev..0. 6

7 Typical Performance Characteristics IDD -ST (µa) Temperature ( C) Figure 6. Startup Current (I DD-ST) vs. Temperature VDD -ON (V) Temperature ( C) 5.0 Figure 8. Start Threshold Voltage (V DD-ON) vs. Temperature VDD-OFF (V) IDD-OP (ma) Temperature ( C ) Figure 7. Operating Supply Current (I DD-OP) vs. Temperature Temperature ( C) Figure 9. Minimum Operating Voltage (V DD-OFF) vs. Temperature 0 SG674A Highly Integrated Green-Mode PWM Controller IHV (ma) I HV-LC (µa) Temperature ( C) Figure 0. Supply Current Drawn from HV Pin (I HV) vs. Temperature Temperature ( C ) 70.0 Figure. Figure Caption f OSC (khz) DCYMAX (%) Temperature ( C ) Temperature ( C ) Figure. Frequency in Nominal Mode (f OSC) vs. Temperature Figure 3. Maximum Duty Cycle (DCY MAX) vs. Temperature 008 Fairchild Semiconductor Corporation SG674A Rev..0. 7

8 Functional Description Startup Current For startup, the HV pin is connected to the line input or bulk capacitor through an external resistor, R HV, which is recommended as 00KΩ. Typical startup current drawn from pin HV is ma and charges the hold-up capacitor through the resistor R HV. When the V DD capacitor level reaches V DD-ON, the startup current switches off. At this moment, the V DD capacitor only supplies the SG674A to maintain V DD before the auxiliary winding of the main transformer provides the operating current. Operating Current Operating current is around 4mA. The low operating current enables a better efficiency and reduces the requirement of V DD hold-up capacitance. Green-Mode Operation The proprietary green-mode function provides an offtime modulation to reduce the switching frequency in the light-load and no-load conditions. The on-time is limited for better abnormal or brownout protection. V FB, which is derived from the voltage feedback loop, is taken as the reference. Once V FB is lower than the threshold voltage, switching frequency is continuously decreased to the minimum green-mode frequency around 8KHz (R I=6KΩ). Oscillator Operation A resistor connected from the RI pin to the GND pin generates a constant current source for the controller. This current is used to determine the center PWM frequency. Increasing the resistance reduces PWM frequency. Using a 6KΩ resistor R I results in a corresponding 65KHz PWM frequency. The relationship between R I and the switching frequency is: 690 fpwm = (KHz) R I (KΩ) () The range of the PWM oscillation frequency is designed as 47kHz ~ 09kHz. Current Sensing and PWM Current Limiting Peak-current-mode control is utilized in SG674A to regulate output voltage and provide pulse-by-pulse current limiting. The switch current is detected by a sense resistor into the SENSE pin. The PWM duty cycle is determined by this current sense signal and V FB, the feedback voltage. When the voltage on the SENSE pin reaches around V COMP = (V FB.)/3., a switch cycle terminates immediately. V COMP is internally clamped to a variable voltage around 0.85V for output power limit. Leading-Edge Blanking (LEB) Each time the power MOSFET is switched on, a turn-on spike occurs on the sense-resistor. To avoid premature termination of the switching pulse, a leading-edge blanking time is built in. During this blanking period, the current-limit comparator is disabled and cannot switch off the gate driver. Under-Voltage Lockout (UVLO) The turn-on and turn-off thresholds are fixed internally at 6.5V and 0.5V. During startup, the hold-up capacitor must be charged to 6.5V through the startup resistor to enable the IC. The hold-up capacitor continues to supply V DD before the energy can be delivered from auxiliary winding of the main transformer. V DD must not drop below 0.5V during startup. This UVLO hysteresis window ensures that hold-up capacitor is adequate to supply V DD during startup. Gate Output / Soft Driving The BiCMOS output stage is a fast totem-pole gate driver. Cross conduction is avoided to minimize heat dissipation, increase efficiency, and enhance reliability. The output driver is clamped by an internal 8V Zener diode to protect power MOSFET transistors against undesirable gate over voltage. A soft driving waveform is implemented to minimize EMI. Built-in Slope Compensation The sensed voltage across the current-sense resistor is used for peak-current-mode control and pulse-by-pulse current limiting. Built-in slope compensation improves stability or prevents sub-harmonic oscillation. SG674A inserts a synchronized positive-going ramp at every switching cycle. Constant Output Power Limit When the SENSE voltage, across the sense resistor R s, reaches the threshold voltage, around 0.9V, the output GATE drive is turned off after a small delay, t PD. This delay introduces an additional current proportional to t PD V IN / L P. Since the delay is nearly constant, regardless of the input voltage V IN, higher input voltage results in a larger additional current and the output power limit is higher than that under low input line voltage. To compensate this variation for wide AC input range, a sawtooth power-limiter is designed to solve the unequal power-limit problem. The power limiter is designed as a positive ramp signal fed to the inverting input of the OCP comparator. This results in a lower current limit at high-line inputs than at low-line inputs. SG674A Highly Integrated Green-Mode PWM Controller 008 Fairchild Semiconductor Corporation SG674A Rev..0. 8

9 V DD Over-voltage Protection (OVP) V DD over-voltage protection has been built in to prevent damage due to abnormal conditions. Once the V DD voltage is over the V DD over-voltage protection voltage (V DD-OVP) and lasts for t D-VDDOVP, the PWM pulses are disabled until the V DD voltage drops below the UVLO, then starts again. Over-voltage conditions are usually caused by open feedback loops. Limited Power Control The FB voltage increases every time the output of the power supply is shorted or overloaded. If the FB voltage remains higher than a built-in threshold for longer than t D-OLP, PWM output is turned off. As PWM output is turned off, the supply voltage V DD begins decreasing. When V DD goes below the turn-off threshold (~0.5V) the controller is totally shut down. V DD is charged up to the turn-on threshold voltage of 6V through the startup resistor until PWM output is restarted. This protection feature continues as long as the overloading condition persists. This prevents the power supply from overheating due to overloading conditions. Noise Immunity Noise on the current sense or control signal may cause significant pulse-width jitter, particularly in continuousconduction mode. Slope compensation helps alleviate this problem. Good placement and layout practices should be followed. Avoiding long PCB traces and component leads, locating compensation and filter components near the SG674A, and increasing the power MOS gate resistance improve performance. SG674A Highly Integrated Green-Mode PWM Controller 008 Fairchild Semiconductor Corporation SG674A Rev..0. 9

10 Reference Circuit CN L T C 3 CN C 3 4 C R3 U SG674A GND GATE FB VDD NC SENSE HV RI VZ R6 BD 4 4 T 8 C3 R4 D3 + C9 C0 R5 + C5 C4 D U R9 A K R U3 R8 C 5 R Q R7 VO+ R0 R Figure 4. Circuit (V/5A) R 3 Q C6 + C7 L4 VO+ + C8 L 3 4 D VO+ VO- SG674A Highly Integrated Green-Mode PWM Controller BOM Reference Component Reference Component BD BD 4A/600V Q MOS 7A/600V C XC 0.68µF/300V R R 00KΩ /W C XC 0.µF/300V R R 47Ω /4W C3 YC pf/y R3 R 00KΩ /W C4 EC 0µF/400V R4 R 0Ω /8W C5 CC 0.0µF/500V R5 R 00Ω /8W C6 CC 0pF/00V R6 R 33KΩ /8W C7 EC 000µF/5V R7 R 0.3Ω W C8 EC 470µF/5V R8 R 680Ω m /8W C9 EC µf/50v R9 R 4.7KΩ /8W C0 CC 470pF/50V R0 R 50KΩ m /8W C CC pf/50v R R 39KΩ /8W C CC 03pF/50V T 0mH D Zener Diode 5V /W (option) T 600µH(PQ60) D BYV95C U IC SG674A D3 FR03 U IC PC87 F FUSE 4A/50V U3 IC TL43 L 900µH VZ VZ 9G Q STP0-00CT 008 Fairchild Semiconductor Corporation SG674A Rev..0. 0

11 Physical Dimensions PIN ONE INDICATOR (0.33).75 MAX R0.0 R (.04) DETAIL A SCALE: : C A M x B SEATING PLANE C BA 0.0 C GAGE PLANE LAND PATTERN RECOMMENDATION SEE DETAIL A OPTION A - BEVEL EDGE OPTION B - NO BEVEL EDGE NOTES: UNLESS OTHERWISE SPECIFIED 5.60 A) THIS PACKAGE CONFORMS TO JEDEC MS-0, VARIATION AA, ISSUE C, B) ALL DIMENSIONS ARE IN MILLIMETERS. C) DIMENSIONS DO NOT INCLUDE MOLD FLASH OR BURRS. D) LANDPATTERN STANDARD: SOIC7P600X75-8M. E) DRAWING FILENAME: M08AREV3 SG674A Highly Integrated Green-Mode PWM Controller Figure 5. 8-Lead Small Outline Package (SOP) Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or obtain the most recent revision. Package specifications do not expand the terms of Fairchild s worldwide terms and conditions, specifically the warranty therein, which covers Fairchild products. Always visit Fairchild Semiconductor s online packaging area for the most recent package drawings: Fairchild Semiconductor Corporation SG674A Rev..0.

12 008 Fairchild Semiconductor Corporation SG674A Rev..0. SG674A Highly Integrated Green-Mode PWM Controller