Application Note 1057 Design and Application Notes for AP3107/H System Solution Prepared by Wang Zhao Kun System Engineering Dept. 100mW, and the application note will show you how to design a SMPS using AP3107/H. 1. Introduction The AP3107/H is a high voltage start-up, current mode PWM controller with green-mode power-saving operation. The AP3107/H is offered in SOIC-7 package to realize a compact size. The AP3107/H is specially designed for ultra low standby power performance. Different from AP3106, AP3107/H PWM switching frequency at normal operation is fixed at 65kHz/130kHz internally with a narrow range. 2. Peripheral Component 2.1 BNO Pin Resistor The AP3107/H has the function of brown-out which can be realized by BNO pin, the brown-out voltage is adjusted by the resistor connected between BNO and GND, the formula of DC input voltage and BNO pin resistor is as the following： Table 1. The differences Between AP3107/H and AP3106 AP3106 Frequency Adjustable FB Resistor 18k Standby Performance Dynamic Performace Application Area AP3107/H Fixed at 65kHz/130kHz 18k—Normal Mode 120k—Burst Mode Better Best Good A Little Bad Adapter LCD Display/Standby Power 2 VON (V ) = 0.0001(V / kΩ 2 ) × R BNO (kΩ) − 0.1284(V / kΩ) × R BNO (kΩ) + 103.41(V ) 2 VOFF (V ) = 0.0001(V / kΩ 2 ) × R BNO (kΩ) − 0.13(V / kΩ) × R BNO (kΩ) + 96.181(V ) Where： VON means AP3107/H starts to work when the voltage on HV pin is higher than VON。 VOFF means AP3107/H does not work when the voltage on HV pin is lower than VOFF。 RBNO is the resistor between BNO pin and GND. 110 The AP3107/H integrates a lot of functions such as green mode, frequency dithering, VCC over voltage protection (VOVP) and line compensation. The green mode and burst mode functions with a low operating current could minimize the power consumed on light load, frequency dithering will help to achieve a good EMI result, VOVP protects the IC from being damaged when VCC voltage is too high in abnormal conditions, and line compensation enables a constant over load protection (OLP). Otherwise, over-temperature protection, soft-start function and brown-out function are also integrated in AP3107/H, and the brown-out range is embedded with a tight range of 70Vac to 80Vac. 105 Brown-out Voltage (V) 100 90 85 Turn on 80 75 Turn off 70 65 60 0 30 60 90 120 150 180 210 240 270 300 330 360 BNO Resistor (kΩ) Figure 1. Brown-out Voltage vs. BNO Resistor The AP3107/H provides the users a high efficiency, low standby power, minimum external component counts and low cost solution for AC/DC power converters especially for LCD power. The standby power of system using AP3107/H could be less than Apr. 2011 95 2.2 HV Protection Resistor HV pin is connected to the high voltage line to start the IC, it can be connected to the line directly, but when the lightning surge test is done, the surge current may go through bulk capacitor positive, if Rev. 1. 0 BCD Semiconductor Manufacturing Limited 1 Application Note 1057 HV pin is connected to the line directly, the lighting noise will influence the IC by the PCB track, so one resistor 20kΩ to 50kΩ should be connected between high voltage line and HV pin. 2.3.2 How to Get a Constant OLP For a constant OLP from 90Vac to 264Vac, there is line compensation in AP3107/H and AP3106, the current limit point with line compensation is as below: V cs = 136 * 10 6 (V * Ω ) − (Vin (V ) − 107 .7 (V )) * ( R ext ( Ω ) + 78850 ( Ω )) 160 * 10 6 ( Ω ) Where Rext is the resistor of RC filter for SENSE pin in Figure 3. Figure 4 is the curve of SENSE pin voltage vs. line voltage when Rext=1k. 1.00 SENSE Pin Voltage (V) 0.95 Figure 2. The Resistors of HV Pin and BNO Pin 2.3 SENSE Design for AP3106 and AP3107/H Series 2.3.1 The RC Filter Function When switch is turned on, there will be a voltage spike (which is caused by parasitic capacitance of primary winding and secondary recovery current) on the current sensing resistor. To avoid false trigger by the voltage spike, there is 250ns LEB (Leading Edge Blanking) time for SENSE pin, but if the time of spike exceeds LEB time, the IC will be triggered falsely too, so the RC filter is necessary. Otherwise when the switch is shut down, there is a negative voltage on current sensing resistor, and the resistor could protect the IC from being damaged. 0.90 0.85 0.80 0.75 0.70 0.65 0.60 0 30 60 90 120 150 180 210 240 270 300 330 360 Line Voltage (V) Figure 4. SENSE Pin Voltage vs. Line Voltage When Rext=1K The formula of input power on OCP point is as the following: For CCM, Pin = Vo * ( Ipeak + Itd − Icomp ) * (1 − D ) * Nt − N t2 * Vo2 * (1 − D ) 2 Lm * fs For DCM, Pin = 1 ( Ipeak + Itd − Icomp) 2 * Lm * fs 2 Where Ipeak is primary peak current which is VCS/RS; Itd is the primary current caused by delay time (td) of IC and system which is VIN*td/LM; Icomp is the current of line compensation on sensing resistor; Nt is turn ratio; LM is primary inductor; fs is switching frequency; D is duty cycle. Figure 3. RC Filter for SENSE Pin Though RC filter is helpful to the IC, it’s time constant should be selected carefully, because it will affect the OCP result of system. By the formula, we can adjust some system parameApr. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 2 Application Note 1057 but power ground can be crossed. ters to receive a better OLP result. (1) Primary Inductance Primary inductance will influence the working mode (CCM and DCM) of system on OLP point, and it will also decide the depth of CCM. DCM is better than CCM on contributing to constant OLP, and deeper CCM has a negative influence on constant OLP, so a lower value of primary inductance will be helpful to constant OLP. (2) RC Filter for SENSE Pin For RC filter, it should be adjusted on practical using, if the line compensation is too large on high line (OCP current on high line is lower than it on low line), increasing RC constant is helpful to constant OLP, if the line compensation is not enough on high line (OCP current on high line is lower than it on low line), decreasing RC constant is a good choice. Figure 5. High Current Loop 3.2 ESD Design Electro-static Discharge (ESD) is an important testing item for switching power supply, the ability of bearing for system could be improved by designing a path to release the electric charge to the ground. (3) Turn Ratio If the line compensation is too large on high line, decreasing turn ratio is useful for constant OLP, if the line compensation is not enough on high line, increasing turn ratio is a good choice. As shown in Figure 6, the red line means the proposed path to release the charge. A copper tip for discharging can be placed between primary side and secondary side, but the distance between two tips should be consistent with the requirement of safety specification. 3. PCB Layout for AP310X Series 3.1 EMI Consideration A proper PCB layout can abate unknown noise interference and EMI issue in the switching power supply. Shown as Figure 5, there are four main huge high frequency current loops: The inductor of common mode filter and differential mode filter will affect the effect of transient discharging, so there should be copper tip with them and the distance should be as short as possible. Another way is placing resistor paralleled with the inductor to replace the copper tip and the value is about 1kΩ to 5kΩ, a smaller resistor is helpful to ESD but has bad influence for lightning surge. 1. The current path from bulk capacitor, transformer, MOSFET, RCS returning to bulk capacitor, path A in Figure 5; 2. The path from GATE pin, MOSFET, RCS returning to the ground of IC, path B in Figure 5; 3. The RCD clamp circuit is a high frequency loop, path C in Figure 5; 4. Transformer, rectifier diode, and output capacitor is also a high frequency current loop, path D in Figure 5. 3.3 Common Mode Lightning Surge Design In common mode lightning surge test, the IC pins may observe the noisy signal which is highly dependent on PCB design, so a good layout could improve the ability of enduring the surge test. “Star” connection is highly recommended for primary GND. As shown in Figure 7, the blue lines mean separated routines tied to GND which are connected together in bulk capacitor negative pin. The primary side of Y-cap can also be connected to the high voltage pin of transformer. They must be as short as possible to decrease the radiation area for a better EMI, and if the MOSFET and Schottky diode have heat sink, they should be connected to the ground separately. Otherwise, the IC should not be placed in the loop of switching power trace, and control signal (low current and low voltage) should not be across switching power trace with pulsating high voltage, Apr. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 3 Application Note 1057 Figure 6. The Path to Release Charge of ESD Figure 7. Star Connection of Primary GND Apr. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 4 Application Note 1057 4. How to Design a Lower Standby Power with 3107/H 50µA current opto-coupler. 4.1 X-capacitor and X-resistor A good quality X-capacitor will be helpful to save the standby power, using a low value X-cap can also decrease the X-cap losses, according to IEC 60950, for the X-cap exceeding 0.1µF, during an interval equal to one constant, the voltage will have decayed to 37% of its original value, and after calculating, the RC value is determined by R×C<1, so for a low value X-cap, a higher value X-resistor can be used, and the losses on X-resistor will be reduced. When system exits the burst mode, the output voltage will go back to normal voltage. 4.2 Bulk Capacitor A good quality bulk capacitor is contributed to low standby power, it can save 20mW to 30mW power relative to poor quality capacitor. in the transistor of Figure 8. Resistor Paralleled with Opto-coupler 4.4 Current Sampling Resistor The value of sampling resistor can affect the standby power, a lower value SENSE resistor is good for low standby power. But it is also relative to the OLP result, a lower value SENSE resistor will make a worse OLP result. 4.3 Opto-coupler Resistor For a low standby power, small current mode technology is used under light load condition. If the system enters burst mode, the pulse of GATE pin is low and the persistent time is over one clock, IC will enter small current mode (the sourcing current of FB pin is about 50µA) to reduce the power consumption of AP3107/H, When system exits burst mode, the AP3107/H will operate at normal current mode. Otherwise, adjusting the opto-coupler resistor (Ropt in Figure 8) which parallels with the opto-coupler could affect the output voltage at small current mode. The current (Iopt in Figure 8) flows in the diode of opto-coupler is relative to the current of FB pin, so Iopt will be a small current. If the current flowing in Ropt and opto-coupler is not enough for shunt regulator, the output voltage at small current mode will be down from the center voltage a little, the higher value the Ropt is, the lower value the output voltage is, and the low output voltage will contribute to the low standby power. The value of Ropt can be calculated by following formula: Ropt > flowing 4.5 The Output Voltage Dividing Resistor The value of output voltage dividing resistor should be as high as possible, but the maximum value of the resistor connected to GND (R17 in Figure 7) should not exceed 15kΩ. 4.6 RCD Clamp Circuit For a better standby power, the RCD clamp circuit may be replaced by a Transient Voltage Suppressor (TVS) and a diode (Figure 9), the advantage of the TVS clamp is that it only conducts when it is really needed and is independent of the switching frequency. Compared to a RCD clamp, it reduces no-load power but increases costs and EMI. Otherwise, a lower value of RC is contributed to standby power, while the voltage stress on MOSFET should be within the spec. Vopt × K I c × K − I FB Where: Vopt is the drop voltage of diode in opto-coupler, the normal value is about 1V; IFB is sourcing current of FB pin at small current mode; IC is the minimum cathode current for regulation of shunt regulator; K is the current transfer rate (CTR) of opto-coupler and the value is about 25% to 30% when there is Apr. 2011 Figure 9. Clamp Circuit with TVS 4.7 RC Clamp on Schottky A low value of RC which paralleled with Schottky is helpful to low standby power, the value should Rev. 1. 0 BCD Semiconductor Manufacturing Limited 5 Application Note 1057 Figure 10 shows the application schematic, and Table 2 is the test result of standby power. It shows the LCD monitor demo board components list. The standby power is less than 100mW in the whole input voltage range while the load are 5V/6mA and 14V/0A, the power is measured by a power meter Chroma 66202. be adjusted to make the voltage stress on Shottky not exceed the spec at turn-on. 5. LCD Monitor Demo Design and Test Result A LCD monitor board using flyback topology is designed, the system specification is as below: Output voltage and current: 14V/2.5A, 5V/2.5A Input voltage range: 90Vac to 264Vac Table 2. Test Results of Standby Power (5V/6mA, 14V/0A) Input Voltage Input Power 90Vac/60Hz 0.057W 115Vac/60Hz 0.060W 180Vac/50Hz 0.049W 230Vac/50Hz 0.087W 264Vac/50Hz 0.095W Figure 10. Application Circuit Schematic Part Value Part Value Note BD1 GUB410 C4 10pF 0805C F1 1A/250V C5 6.8nF 0805C RT1 5D-9 1nF/1kV 0805C R1, R2 2MΩ 1206R C6，C7 C8 680µF/16V Electrolytic R3, R4 20kΩ 1206R C9 680µF/10V Electrolytic R5 100kΩ 0805R C10 470µF/16V Electrolytic R6 100kΩ Axial-1W C11 Electrolytic R7 2.2Ω 1206R C12 470µF/10V 22nF Apr. 2011 Note Rev. 1. 0 0805C BCD Semiconductor Manufacturing Limited 6 Application Note 1057 Part R8 R9 R10 R11 R12 R13 R14 Value 10Ω 100kΩ 1kΩ 0.39Ω 10Ω 20Ω 150Ω Note 0805R 0805R 0805R Axial-1/2W 1206R 1206R 0805R Part CX1 CY1 L1 L2 L3 D1 D2 Value 0.22µF 1nF 30mH 2.2µH 2.2µH FR107 1N4007 DO-41 DO-41 R15 7.5kΩ 0805R D3 1N4148 1206 R16 20kΩ 0805R D4 MBR10150 BCD Semi R17 18kΩ 0805R D5 MBR10100 BCD Semi R18 180kΩ 0805R U1 AP3107/H SOIC-7 R19 12kΩ 0805R U2 PC817C Sharp C1 Electrolytic U3 AZ431 BCD Semi C2 100µF/400V 2.2nF/1kV Ceramic Q1 STP6NK60Z TO-220 C3 47µF/50V Electrolytic T1 ER28 Apr. 2011 Rev. 1. 0 Note X-cap X-cap 0.8A BCD Semiconductor Manufacturing Limited 7