MT6258C

AEROSEMI MT6258C Current Mode PWM Power Switch Features  Power on Soft Start Reducing MOSFET Vds Stress  Frequency Shuffling for EMI  Extended Burst Mode Control For Improving Efficiency and Minimum Standby Power Design Audio Noise Free Operation Fixed 55KHZ Switching Frequency Internal Synchronized Slope Compensation Low VDD Start-up Current and Low Operating Current Leading Edge Blanking on Current Sense Input VDD Over Voltage Clamp and Under Voltage Lockout with Hysteresis (UVLO) Line Input Compensated Cycle-by-Cycle OverCurrent Threshold Setting For Constant Output Power Limiting Over Universal Input Voltage Range. Over Load Protection(OLP). Over Voltage Protection(OVP). Applications Offline AC/DC fly-back converter for  AC/DC adapter       PDA Power Supply Digital Cameras and Camcorder Adapter VCR,SVR, STB, DVD&DVCD Player SMPS Set- Top Box Power Auxiliary Power Supply for PC and Server Open-frame SMPS General Description MT6258C combines a dedicated current mode PWM controller with a high voltage power MOSFET. It is optimized for high performance, low standby power, and cost effective off-line fly-back converter applications in sub 27W range. MT6258C offers complete protection coverage with automatic self-recovery feature including Cycle-by-Cycle Current Limiting (OCP), Over Load Protection (OLP), VDD Over Voltage Clamp and Under Voltage Lockout (UVLO). Excellent EMI performance is achieved with frequency shuffling technique together with soft switching control at the totem pole gate drive output. The tone energy at below 20KHZ is minimized in the design and audio noise is eliminated during operation. MT6258C is offered in DIP8 package. Typical Application MT6258C V 1.1 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 1 AEROSEMI Power Switch Marking information MT6258C Freq Shuffling DIP8 Terminal Assignments Pin number 1 2 Current Mode PWM Pin name VDD_G VDD 3 FB 4 SENSE 5,6 DRAIN 7,8 GND Description Internal Gate Driver Power Supply IC DC power supply Input Feedback input pin. The PWM duty cycle is determined by voltage level into this pin and the current-sense signal at Pin 4. Current sense input HV MOSFET Drain Pin. The Drain pin is connected to the primary lead of the transformer GND Absolute Maximum Ratings Parameter Value Drain Voltage (off state) VDD Voltage VDD-G Input Voltage VDD Clamp Continuous Current FB Input Voltage Sense Input Voltage Min/Max Operating Junction Temperature TJ Min/Max Storage Temperature TSTG Lead Temperature (Soldering, 10secs) Range -0.3 to BV DSS -0.3~30 -0.3~30 10 -0.3~7 -0.3~7 -20 to 150 -55 to 150 260 Unit V V V mA V V ℃ ℃ ℃ Note: Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not implied. Exposure to absolute maximum-rated conditions for extended periods may affect device reliability. Output power table Product MT6258C MT6258C V 1.1 230VAC±15% Open Frame 27W 85-265VAC Open Frame 16W www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 2 AEROSEMI MT6258C Current Mode PWM Electrical Characteristics Freq Shuffling Power Switch （If not otherwise noted，VDD =VDD-G=16 V, TA =25 ℃） Symbol Parameter Supply voltage(VDD) I_startup VDD Start up Current I_VDD_OP Operation Current UVLO(ON) VDD Under Voltage Lockout Enter Test Conditions VDD =14.5V,Measure Leakage current into VDD Over voltage Protection voltage Type Max Unit 5 20 CS=0V,FB=3V Ramp up VDD until gate clock is off uA 1.6 VFB = 3V VDD Under Voltage Lockout UVLO(OFF) Exit(recovery) OVP(ON) Min mA 7 8 9 V 15.2 16.2 17.2 V 27.5 29 30.5 V Current Sense Input(sense pin) 4 ms Leading edge Blanking time 270 ns Input Impedance 40 KΩ 120 ns Soft Start Time TLEB ZSENSE_ IN TD_ OC Over Current Detection and Control Delay VTH_ OC Current Limiting Threshold Voltage From Over Current Occurs till the Gate drive output start to turn off FB=3.3V 0.72 0.75 0.78 V 5.4 5.7 6.0 V Feedback Input Section(FB Pin) VFB_ Open VFB Open Loop Voltage IFB_ Short FB pin short circuit current VTH_ 0D Short FB pin to GND and measure current 0.4 mA Zero Duty Cycle FB Threshold Voltage 0.8 V VTH_ PL Power Limiting FB Threshold Voltage 3.7 V TD _PL Limiting Debounce time 50 ms ZFB_ IN Input Impedance 4 KΩ Oscillator FOSC MT6258C V 1.1 Normal Oscillation Frequency 50 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 55 60 KHz 3 AEROSEMI Power Switch △f_Temp △f_VDD MT6258C Current Mode PWM Freq Shuffling Frequency Temperature Stability 5 % Frequency Voltage Stability 5 % D_max Maximum Duty Cycle F_Burst Burst Mode Base Frequency FB=3.3V, CS=0V 70 80 % 90 22 KHz MOSFET Section BVdss MOSFET Drain-Source Breakdown Voltage Rdson Static, Id=1A 600 V 4 Ω Frequency Shuffling △f_ OSC MT6258C V 1.1 Frequency Modulation range Base frequency -4 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. % 4 4 AEROSEMI Block Diagram Power Switch MT6258C V 1.1 MT6258C Current Mode PWM Freq Shuffling www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 5 AEROSEMI MT6258C Current Mode PWM Operation Description Freq Shuffling Power Switch The MT6258C is a low power off-line SMPS Switcher optimized for off-line fly-back converter applications in sub 27W power range. The ‘Extended burst mode’ control greatly reduces the standby power consumption and helps the design easily to meet the international power conservation requirements. Start up Current and Start up Control Start up current of MT6258C 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 start-up resistor can therefore be used to minimize the power loss yet achieve a reliable start-up in application. For AC/DC adapter with universal input range design, a 2MΩ, 1/2W start-up resistor could be used together with a VDD capacitor to provide a fast start-up and yet low power dissipation design solution. Operating Current The Operating current of MT6258C is low at 1.6mA(typical). Good efficiency is achieved with MT6258C low operating current together with the ‘Extended burst mode’ control features. Soft Start MT6258C features an internal 4ms soft start to soften the electrical stress occurring in the power supply during start-up. 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 0.75V. Every restart up is followed by a Soft Start Frequency shuffling for EMI improvement The frequency Shuffling (switching frequency modulation) is implemented in MT6258C. 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 mode 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 power 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 orMT6258C no load condition, the FB input dropswww.aerosemi.com below burst mode threshold level and device enters V 1.1 Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 6 AEROSEMI MT6258C Current Mode PWM Burst Mode control. The Gate drive output switches only when VDD voltage drops below a Freq Shuffling Powerlevel Switch preset 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 MT6258C is internally fixed at 55KHZ. 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 MT6258C 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 gate current of internal power MOSFET so that the 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 subharmonic oscillation and thus reduces the output ripple voltage. Drive The internal power MOSFET in MT6258C 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 trade off 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 dedicated 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 Control MT6258C V 1.1 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 7 AEROSEMI Power Switch MT6258C Current Mode PWM Freq Shuffling 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 TD_PL, control circuit reacts to shut down the switcher. Switcher restarts when VDD voltage drops below UVLO limit. VDD is supplied by transformer auxiliary winding output. when VDD voltage exceeds the internal OVP threshold voltage, and the output of MT6258C is shut down.when VDD drops below UVLO_on limit and Switcher enters power on start-up sequence thereafter. MT6258C V 1.1 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 8 AEROSEMI MT6258C Current Mode PWM PACKAGE MECHANICAL DATA Freq Shuffling Power Switch DIP8 Package Outline DIMENSIONS Symbol A A1 A2 B 1 B1 1 C A 1 D 1 E E1 DQ e SD D L S Q X E2 W X S D Q D W D MT6258C V 1.1 Dimensions In Millimeters Min Max 3.710 5.334 0.381 2.921 4.953 0.350 0.650 1.524(BSC) 0.200 0.360 9.000 10.16 00 6.096 7.112 7.320 8.255 2.540 2.921 (BSC) 3.810 7.620 10.92 0 Dimensions In Inches Min Max 0.146 0.210 0.015 0.115 0.195 0.014 0.026 0.06(BSC) 0.008 0.014 0.354 0.400 0.280 0.240 0.288 0.325 0.1 (BSC) 0.115 0.150 0.300 0.430 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 9