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Technical content
Features
Power on soft start reducing MOSFET VDS stress Frequency shuffling for EMI Extended burst mode control for improved efficiency and minimum standby power design Audio noise free operation Fixed 50kHz switching frequency Internal synchronized slope compensation Low VDD startup current and low operating current Leading edge blanking on current sense input Good protection coverage with auto self -recovery: VDD over voltage clamp and under voltage lockout with hysteresis (UVLO) Line input compensated cycle-by-cycle over-current threshold setting fo r constant output power limiting over universal input voltage range Over load protection (OLP) Over voltage protection(OVP)
Applications
Battery charger PDA power supplies Digital cameras and camcorder adaptor VCR, SVR, STB, DVD&DVCD player SMPS Set-top box power Auxiliary power supply for PC and server Open-frame SMPS Figure 1. Package Type
Figure 2. Pin Configuration
1 VDD-G Internal gate driver power supply
2 VDD Chip DC power supply pin
4 SENSE Current sensing input
Table 1. Pin Description
Figure 3. Functional Block Diagram
December, 2013 Rev. 1.1 4/13 ©2013 Shaoxing Devechip Microelectronics Co., Ltd. www.sdc-semi.com Current Mode PWM Power Switch SDC4108
Ordering Information
DIP-8: Z E1: Pb-free G1: Halogen-free Blank: Tube X X - X Package Temperature Range Part Number Marking ID Packing Type Pb-free Halogen-free Pb-free Halogen-free DIP-8 -40℃~85℃ SDC4108Z -E1 SDC4108Z -G1 SDC4108 SDC4108G Tube Output Power Table Product 230VAC±15% 85-265VAC SDC4108 16W 9W Table 2. Output Power
Table 3. Absolute Maximum Ratings Table 4. Recommended Operating Conditions
Table 5. Electrical Characteristics
Figure 10. Rdson(Ω) vs. Temperature(°C)
December, 2013 Rev. 1.1 9/13 ©2013 Shaoxing Devechip Microelectronics Co., Ltd. www.sdc-semi.com Current Mode PWM Power Switch SDC4108 Operation Description The SDC4108 is a low power off -line SMPS switcher optimized for off -line flyback converter applications in sub 16W power range. The extended burst mode control greatly reduces the standby power consumption an d helps the design easily to meet the international power conservation requirements. Startup Current and Start up Control Startup current of SDC4108 is designed to be very low so that VDD could be charged up above UVLO threshold level and device starts up quickly. A large value startup resistor can therefore be used to minimize the power loss yet achieve a reliable startup in application. For AC/DC adaptor with universal input range design, a 2 MΩ, 1 / 8 W startup resistor could be used together with a VDD capacitor to provide a fast startup and yet low power dissipation design solution. Operating Current The operating current of SDC4108 is low at 2mA. Good efficiency is achieved with SDC4108 low operating current together with the extended burst mode control features. Soft Start SDC4108 features an internal 4ms soft start to soften the electrical stress occurring in the power supply during startup. It is activated during the power on sequence. As soon as VDD reaches UVLO(OFF), the peak current is gradually increased from nearly zero to the maximum level of 0.77V. Every restart up is followed by a soft start. Frequency shuffling for EMI improvement The frequency shuffling (switching frequency modulation) is implemented in SDC4108. The oscillation frequency is modulated so that the tone energy is spread out. The spread spectrum minimizes the conduction band EMI and therefore eases the system design. Extended Burst Mode Operation At light load or zero load condition, most of the power dissipation in a switching mod e power supply is from switching loss on the MOSFET , the core loss of the transformer and the loss on the snubber circuit. The magnitude of power loss is in proportion to the switching frequency. Lower switching frequency leads to the reduction on the powe r loss and thus conserves the energy. The switching frequency is internally adjusted at no load or light load condition. The switch frequency reduces at light/no load condition to improve the conversion efficiency. At light load or no load condition, the FB input drops below burst mode threshold level and device enters burst mode control. The gate drive output switches only when VDD voltage drops below a preset level and FB input is active to output an on state. Otherwise the gate drive remains at off state to minimize the switching loss and reduces the standby power consumption to the greatest extend. The switching frequency control also eliminates the audio noise at any loading conditions. Oscillator Operation The switching frequency of SDC4108 is internally fixed at 50kHz. No external frequency setting components are required for PCB design simplification. Current Sensing and Leading Edge Blanking Cycle-by-cycle current limiting is offered in SDC4108 current mode PWM control. The switch current is detected by a sense resistor into the sense pin. An internal leading edge blanking circuit chops off the sensed voltage spike at initial internal power MOSFET on state due to snubber diode reverse recovery and surge SDC CONFIDENTIAL DOCUMENT
December, 2013 Rev. 1.1 10/13 ©2013 Shaoxing Devechip Microelectronics Co., Ltd. www.sdc-semi.com Current Mode PWM Power Switch SDC4108 gate current of internal power MOSFET so that th e external RC filtering on sense input is no longer needed. The current limiting comparator is disabled and cannot turn off the internal power MOSFET during the blanking period. The PWM duty cycle is determined by the current sense input voltage and the FB input voltage. Internal Synchronized Slope Compensation Built-in slope compensation circuit adds voltage ramp onto the current sense input voltage for PWM generation. This greatly improves the close loop stability at CCM and prevents the sub -harmonic osci llation and thus reduces the output ripple voltage. Gate Drive The internal power MOSFET in SDC4108 is driven by a dedicated gate driver for power switch control. Too weak the gate drive strength results in higher conduction and switch loss of MOSFET while too strong gate drive results the compromise of EMI. A good tradeoff is achieved through the built -in totem pole gate design with right output strength and dead time control. The low idle loss and good EMI system design is easier to achieve with this dedi cated control scheme. In addition to the gate drive control scheme mentioned, the gate drive strength can also be adjusted externally by a resistor connected between VDD and VDDG, the falling edge of the DRAIN output can be well controlled. It provides great flexibility for system EMI design. Protection Controls Good power supply system reliability is achieved with its rich protection features including cycle-by-cycle current limiting (OCP), over load protection (OLP) and over voltage clamp, under voltage lockout on VDD (UVLO). the OCP is line voltage compensated to achieve constant output power limit over the universal input voltage range. At overload condition when FB input voltage exceeds power limit threshold value for more than T D_PL, control circuit re acts to shut down the switcher. Switcher restarts when VDD voltage drops below UVLO limit. VDD is supplied by transformer auxiliary winding output. It is clamped when VDD is higher than 30V. The output of SDC4108 is shut down when VDD drops below UVLO_ON l imit and switcher enters power on start -up sequence thereafter. SDC CONFIDENTIAL DOCUMENT
Figure 11. Typical Application
December, 2013 Rev. 1.1 12/13 ©2013 Shaoxing Devechip Microelectronics Co., Ltd. www.sdc-semi.com Current Mode PWM Power Switch SDC4108
Package Information
Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 3.710 4.310 0.146 0.170 A1 0.510 0.020 A2 3.200 3.600 0.126 0.142 B 0.380 0.570 0.015 0.022 B1 1.524(BSC) 0.060(BSC) C 0.204 0.360 0.008 0.014 D 9.000 9.400 0.354 0.370 E 6.200 6.600 0.244 0.260 E1 7.320 7.920 0.288 0.312 e 2.540(BSC) 0.100(BSC) L 3.000 3.600 0.118 0.142 E2 8.400 9.000 0.331 0.354 SDC CONFIDENTIAL DOCUMENT
December, 2013 Rev. 1.1 13/13 ©2013 Shaoxing Devechip Microelectronics Co., Ltd. www.sdc-semi.com Current Mode PWM Power Switch SDC4108 Shaoxing Devechip Microelectronics Co., Ltd. http://www.sdc-semi.com/ IMPORTANT NOTICE Information in this document is provided solely in connection with Shaoxing Devechip Microelectronics Co., Ltd. (abbr. SDC) products. SDC reserves the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at anytime, without notice . SDC does not assume any responsibility for use of any its products for any particular purpose, nor does SDC assume any liability arising out of the application or use of any its products or circuits. SDC does not convey any license under its patent rights or other rights nor the rights of others. © 2013 Devechip Microelectronics - All rights reserved Contact us: Headquarters of Shaoxing Address: Tian Mu Road, No13, Shaoxing city, Zhejiang province, China Zip code: 312000 Tel: (86) 0575-8861 6750 Fax: (86) 0575-8862 2882 Shenzhen Branch Address: 22A, Shangbu building, Nan Yuan Road, No.68, Futian District, Shenzhen city, Guangdong province, China Zip code: 518031 Tel: (86) 0755-8366 1155 Fax: (86) 0755-8301 8528 SDC CONFIDENTIAL DOCUMENT