AN-6300 FAIRCHILD | Alldatasheet
Document overview
- Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
- PDF pages: 13
Technical content
www.fairchildsemi.com © 2009 Fairchild Semiconductor Corporation www.fairchildsemi.com AN-6300 FAN6300 / FAN6300A / FAN6300H Highly Integrated Quasi-Resonant PWM Controller Abstract This application note describes a detailed design strategy for higher-power conversion efficiency and better EMI using a Quasi-Resonant PWM cont roller compared to the conventional, hard-switched converter with a fixed switching frequency. Based on the proposed design guideline, a design example with detailed parameters demonstrates the performance of the controller. Introduction The highly integrated FAN6300/A/H PWM controller provides several features to enhance the performance of flyback converters. FAN6300/A are applied on Quasi- Resonant flyback converter where maximum operating frequency is below 100kHz and FAN6300H is suitable for high frequency operation that is around 190kHz. A built-in High Voltage (HV) startup circuit can provide more startup current to reduce the startup time of the controller. Once the VDD voltage exceeds the turn-on threshold voltage, the HV startup function is disabled immediately to reduce power consumption. An internal valley voltage detector ensures power system operates in quasi-resonant operation in wide- range line voltage and reduces switching loss to minimize switching voltage on drain of the power MOSFET. To minimize standby power consumption and improve light- load efficiency, a proprietary green-mode function provides off-time modulation to decrease switching frequency and perform extended valley voltage switching to keep to a minimum switching voltage. FAN6300/A/H controller provides many protection functions. Pulse-by-pulse current limiting ensures the fixed peak current limit level, even when short-circuit occurs. Once an open-circuit failure occurs in the feedback loop, the internal protection circuit disables PWM output immediately. As long as V DD drops below the turn-off threshold voltage, the controller also disables the PWM output. The gate output is clamped at 18V to protect the power MOS from high gate-source voltage conditions. The minimum t OFF time limit prevents the system frequency from being too high. If the DET pin reaches OVP level, internal OTP is triggered, and the power system enters latch-mode until AC power is removed.
© 2009 Fairchild Semiconductor Corporation www.fairchildsemi.com To determine the primary-side inductance ( LP), the following variables should be determined beforehand: The minimum switching frequency ( fs,min): The maximum average input current occurs at the minimum input voltage and full-load condition. Meanwhile, the switching frequency is at minimum value during QR operation. The falling time of the MOSFET drain voltage (t f): As shown in Figure 4, the falling time of MOSFET drain voltage is half of the resonant period of the MOSFET effective output capacitance and primary- side inductance. If a resonant capacitor is added to be paralleled with C oss, tf can be increased and EMI can be reduced. However, this forces a switching loss increase. The typical value of tf for NB adaptor application is about 0.5~1μs. After determining fs,min and tf, the maximum duty cycle is calculated as: od max s,min f od i n nV+ VD( 1 - f t ) n V +V +V ()= () (3) where Vin,min is specified at low-line and full-load. According to Equation 1, the maximum average input current Iin,max is determined as oo in,max in,min VII V η = (4) According to Figure 3, Iin,max can be obtained as: pk in,max max ds,max 1ID I (5) Ids,max pk can be determined as: pk in,min max ds,max ms , m i n VD I Lf (6) In Equation 5, replace Ids,max pk by Equation 6, then combine Equations 4 and 5 to obtain LP: in,min max P in s,min (V D L 2P f )= (7) where Pin, and Dmax are specified in Equations 1 and 3, respectively, and fs,min is the minimum switching frequency. Once LP is determined, the RMS current of the MOSFET in normal operation are obtained as: rms peak max ds,max ds,max DII = (8) [d] Determine the Proper Core and the Minimum Primary Turns When designing the transformer, consider the maximum flux density swing in normal operation ( Bmax). The maximum flux density swing in normal operation is related to the hysteresis loss in the core, while the maximum flux density in transient is related to the core saturation. From Faraday’s law, the minimum number of turns for the transformer primary side is given by: pk 6Pd s , m a x P,min max e LI N1 0 BA = (9) where: LP is specified in Equation 7; Ids,max pk is the peak drain current specified in Equation 6; Ae is the cross-sectional area of the core in mm 2; and Bmax is the maximum flux density swing in tesla. Generally, it is possible to use Bmax =0.25~0.30 T. Determine the Number of Turns for Auxiliary Winding The number of turns for auxiliary winding (Na) can be obtained by: DD D1 a od V+ VN= V+ V (10) where: VDD is the operating voltage for VDD pin; VD1 is the forward voltage drop of D1 in Figure 5; and Vo and Vd as determined in Equation 2.
destroyed by external high-voltage during the process. This device is sensitive to electrostatic discharge (ESD). circuit board layout and design a very important issue. should be connected first, then to other circuitry. FAN6300/A/H for good decoupling. sense signals common impedance interference. pointed ends should be at least 5mm. Figure 23. Layout Considerations
Table 1. System Specification calculated and summarized as shown in Table 2. Table 2. Critical System Parameters Figure 24. Complete Circuit Diagram
Table 3. Bill of Materials
© 2009 Fairchild Semiconductor Corporation www.fairchildsemi.com Related Datasheets FAN6300 — Highly Integrated Quasi-Resonant Current PWM Controller DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION, OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, or (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.