BM6312 FEATURES GENERAL DESCRIPTION APPLICATIONS. High-performance current mode PWM Controller. Product Specification

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1 GENERAL DESCRIPTION BM6312 is a high-performance current mode PWM control IC designed for AC/DC convertor, which built-in high-voltage power switch tube and supplies continuous output power of 12W within the range of wide-voltage between 85V and 300V, the output power of peak value can be up to 15W.The combination of optimized reasonable circuit design and bipolar facture technology with high performance and price ratio economizes the whole cost ultimately. The power controller can be applied to the typical flyback circuit topology so as to form a simple AC/DC transformer. IC circuit can use the power switch tube itself within a larger version of startup, greatly reduces the power loss of starting resistance.ic built-in PFM function that when the output power increases then the working frequency increases, thus reducing switching loss and achieving high efficiency when the power output decreases. The PFM function combination of patent drive circuit that can easily meet "of energy Star 2.0" strict requirements. When VCC reaches 12V, the chip internal over voltage protection activates and limits the output voltage rising. That can prevent the too high output voltage because the light coupling or the feedback circuit damaged. The circuit built-in the input voltage compensation function, which realizes the constant output power limiting in the whole power grid conditions. In the IC internal that provides the overload and the perfect saturation function. It can real time control van overload, transformer saturation, output short circuit in abnormal condition, so improving the reliability of power supply. IC has integrated the internal temperature protection function, when the system is overheating, the output power will be lower, or shuts down the output. We can provide meeting ROHS and green environmental protection requirements of DIP-8 standard. FEATURES Meeting AC85-300V input voltage range of the design requirements Low starting current and working current The standby power consumption can be as low as 0.15W Improve driving circuit efficiency 2-3% Meeting the requirements of energy efficiency energy star 2.0 With temperature compensation function accurate current control Wide voltage continuous output power can be up to 12W, the peak output power can be up to 15W AC line compensation With functions of thermal protection (OTP) With functions of over voltage protection (OVP) Can be realized without Y capacitor system design Less peripheral components, and the overall scheme of low cost APPLICATIONS The charger DVD/DVB power Small appliances (such as: induction cooker) PC&LCD TV standby power supply The power adapter (such as communications terminal products)

2 TYPICAL APPLICATION BM6312 Figure 1 Typical application diagram

3 GENERALINFORMATION Pin Configuration The pin map is shown as below for DIP-8 Absolute Maximum Ratings Power supply voltage VCC Pins input voltage 18V VCC+0.3V VIN VCC GND BM6312 OC OC IS Endurance voltage of OC collector V Switching current of peak value 1200mA Total dissipation power 1500mW Operating temperature range -20 to +125 NC FB Deposit temperature range -55 to +150 Welding temperature +260,10S TERMINAL ASSIGNMENTS Pin Num. Pin Name I/O Description 1 VIN I Circuit input compensation and high voltage current source to trigger feet, external compensation resistance 2 VCC P Power Supply 3 GND P Ground 4 NC No Connection 5 FB I Feedback pins 6 IS I Switching current sampling and limit enactment, sampling resistance of external current 7/8 OC O Output pins, meet switching transformer Recommended operating conditions PARAMETER MIN TYP MAX UNIT Power supply voltage VCC 5 10 V Pins input voltage Vcc V Peak inverse voltage V Switching current of peak value ma Operating temperature

4 BLOCK DIAGRAM Figure 2 schematic diagram

5 ELECTRICAL CHARACTERISTICS (Ta=25, VCC= V, RS=1Ω, if not otherwise noted) Parameter Symbol Test Conditions Min Typ Max Unit Output Section Max withstanding voltage of the switching tube I_OC=10mA 750 V Saturation voltage Vsat I_OC=500mA 0.8 V Output Rise time T R CL=1nF 75 ns Output Fall time T F CL=1nF 75 ns Current Sampling Section Current sampling threshold V The maximum current RS=1Ω A Transmission delay ns Oscillator Section Oscillating Frequency F_ OSC 65 KHz Voltage stability VCC=5-10V 1 % Temperature stability Ta= % Leading edge blanking time ns Feedback Section FB Input impedance PWM Section Pull up Current ua Pull down Resistor KΩ Maximum Duty Ratio D_ max VFB=2.5V % Minimum Duty Ratio D_ min VFB=0V % Power Supply Current Section Initiation Static Current ua Static Current I Q VCC=8.0V ma High voltage current source Vac>80V 1.0 ma Startup voltage V Oscillator turn off voltage V Over Voltage limiting Threshold V

6 OPERATION DESCRIPTION Start control: During start-up phase, the internal benchmark, oscillators, driving circuit and protection circuit is stopped working, the small current of 50uA on the starting resistance is input from VIN to the base of the Power Transistor, the amplifying current from Emitter through current limiting circuit outflows to VCC, more than 50uA current part charge to parallel capacitor of VCC, when VCC voltage rises to 8.9 V, entering a state of PWM control chip. PWM control: The voltage of FB pins through the partial pressure resistance exports to the PWM comparator as the peak switching current reference, the FB signal determines the size of the switch tube peak current, through the FB to realize the control of the PWM control. At the same time the Output pulse duty ratio is limited by maximum duty cycle, the FB is controlled by internal and external feedback circuit. External feedback circuit: After amplification the system output error adjusting signal is converted into current signal that can adjust the voltage of FB by isolation transmission of the optocoupler. The heavier load, the smaller optocoupler current, the higher FB voltage, the greater duty ratio of PWM signal, the output power increases, and vice versa, the load is light, the feedback current is added, the FB voltage decreases, the duty ratio decreases, and the output decreases, so as to realize the adjustment of the output voltage. VCC overvoltage protection circuit: if the peripheral feedback makes the VCC increasing that is more than 12V, then the internal feedback circuit makes the FB voltage reducing and reducing the output power, it makes the VCC voltage keeping in 12V, this feature can prevent the output voltage increasing because the optocoupler or feedback is damaged. Thus the secondary circuit and its output load will not damage. Standby frequency reduction control circuit: In standby mode, when the output voltage increases, then the FB voltages lower. If the FB voltage is less than 1.8V (about between V) then the oscillator cycle will increase, the smaller FB, the wider oscillator cycle. This feature is to reduce the standby power consumption and prevent the occurrence of audio interference at the same time. Efficient driving circuit: The efficient driving circuit makes the switch tube in critical saturation driving state, improving the frequency of the triode, effectively reducing the triode switch loss, improving the work efficiency of the whole system, greatly reducing the fever of the chip at the same time. That makes the system more reliable. Ac line compensation: The chip from VIN detects the voltage size and real-time compensate the maximum output power; this makes the maximum limiting power constant. When high and low ac is input. Thermal protection function: When the internal temperature is higher than 140, then making the internal FB voltage reducing and the oscillator cycle widening, reducing or closing the power output, so the BM6312 temperature does not exceed 150 in order to achieve protection.

7 Electric Parameter Definitions Start-up static current: The minimum current sourcing current which can enable VCC surging when VCC is connected to a filter capacitor and an adjustable current sourcing. Start-up voltage: The maximum of VCC above. Restart-up voltage: The minimum of VCC above. Oscillator shut-down voltage: The Negative edge of VCC above; the value of VCC which can stop the oscillator. Static current: The VCC power supply current in normal period when FB is connected to the ground by a 1.0KΩ resistance. FB pull up current: which occurs in normal period, when FB=2.5V, and IS=0A. FB upper current protection: The pull down current of FB when FB=2.0V and IS=0.3A in normal period. The VCC voltage limit: The value of VCC when there is no feedback circuit of BM6312 in normal period. OC upper limit current: If FB=2.0V, the minimum OC current when there is pull down current in FB. Application information FB feedback and control In normal working state, the FB voltage will determine the maximum switching current value, the higher the voltage, the bigger switch current (only limited to peak current limit). The FB pin internal pull-up 550uA current source, pull-down about 40KΩ resistor (approximate equivalent), An external resistor reduces the depth of the feedback, the size of the external resistance will not affect the maximum peak current, it is recommended to use 7.5K to 10K resistor, an external resistor can improve reaction speed of the system with overload and the input voltage jumping. It is advantageous to the short circuit protection. Moreover the FB voltage below 1.8V, will make the period of oscillation widening, the switch frequency falling, It is lower than 1.8V, the frequency will be lower. FB converter capacitance will affect feedback bandwidth, thus influence some external parameters, such as transient characteristics. Figure 3. FB feedback and control

8 Typical applications for CFB capacitance value, can be between nF selection based on the frequency characteristics of the feedback loop, General application can use the 100nF. Over temperature protection IC has built-in precision over temperature protection function. In the chip internal when the temperature reaches 140, the thermal protection circuit pulls down the clock signal, and the switch frequency is reduced in order to reduce the power consumption. The Switching frequency decreases with the rise of the temperature, and until the oscillation shuts down. As shown in the figure below Figure5 The collector emitter clamping voltage Offset waveform as shown in the figure below: Figure 4.Over temperature protection Power tube driving characteristics and high pressure offset technology In the IC internal, it has an unique offset technology, at the time of power tube shutting off, the base output of Power Transistor drops down to the ground instantly, at the same time the offset output voltage of emitter is greater than the base. Launching E junction reverse, it accelerates the I C current rate of descent and expands the effective security work area, The CB of the switch tube is in the reverse voltage that achieves greater than 750V voltage. About more details of the switch tube please refer to the relevant technical data compression characteristics. Figure 6 Vbe driving voltage waveform Over voltage and under-voltage protection IC has with hysteresis under voltage protection function. When the VCC voltage achieves to 8.9 V the IC will start, the initial voltage is provided by a driving resistor, the input of high voltage through the driving resistor enters to B injection of the switch tube, the amplifying IC current through current limiting circuit outflows to VCC capacitor Thus forming the driving voltage. The VCC voltage should be maintained in between 5-10V (including full load)in the normal working,if the VCC voltage pulls down to 2.5V the oscillator will enter closed state.

9 In IC internal, the VCC has an upper limit voltage comparator control, if the VCC is more than 12V the comparator actions, the FB will be drop-down, locking the VCC in 12V, achieving over-voltage limit function. Use this function, it can easily achieve front end voltage feedback function; also can avoid the output voltage rising significantly in the open loop, guaranteeing the safety of the load. Therefore, the VCC should keep in a suitable range and avoid the VCC rising too high with large output loads, leading to the output voltage dropping because the IC overvoltage limitation. Coil larges current programming and driving current compensation circuit Figure 7 Coil larges current programming and driving current compensation circuit The IC has a current limiting function. Each switching cycle detects the switching current, when it achieves the setting current of the FB or the upper limit of the current, then entering the closed cycle, the current detection has the functions of real-time leading edge blanking, shielding switching peak, avoiding error detection of the switching current. The reasonable temperature compensation eliminates the influence of the temperature, relative to conventional transistor, the switching current in a wide range can be very accurate, this don't have too big margin when designing scheme, then can satisfy work in big temperature range, improving the use safety of the circuit. Inside the IS chip connects a resistor R1 to the ground, using to compensate the influence of the internal drive current to the coil current. Its corresponding relationship is I drive*r1=0.7v, the biggest coil current is calculated according to the volume of power, this can be made of the external resistance R2 programming, its relationship is: I winding (Max)=0.7/R2. As a result of the existence of the internal resistor R1. When calculating the R2 value will not consider the influence of the internal drive current to the coil current.

10 The heat dissipation requirements As a result of the drive technology breakthrough, the chip internal loss (fever) 40% less than the PIN TO PIN the other products, but for a typical power switch, should use the necessary cooling measures, in order to avoid high temperature lead to thermal protection. In the IC internal, this main heating is the generated by the switching loss, so the appropriate cooling position is the IC Pin7-8 feet, an easy to use method is laid a certain area of PCB copper foil in Pin7-8 feet, especially it will increase thermal capacity on copper foil tinning, For a V input, typical application of 12W output, 200mm ² is the size of copper foil is necessary. VCC design points When the VCC voltage rises to 8.9V, the IC will start, the VCC capacitor will store enough power for IC before entering normal working until establishing normal output voltage; So the VCC capacitor is not too small, and the reasonable VCC capacitor is 22uF. Figure 8 Heat dissipation map

11 Package size Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A A A B B (BSC) 0.060(BSC) C D E E e 2.540(BSC) 0.100(BSC) L E

12 IC reference junction temperature and thermal resistance IC reference junction temperature and thermal resistance DIP8 encapsulating junction temperature data (θjc)1 25 /W (θja)2 70 /W Note: 1. The test points to Pin7, 8 close to encapsulate the position. 2. Pin7, 8 are connected in a 2 oz copper area of not less than 200mm². BM6312