ISL6841EVAL3Z Evaluation Board for General Purpose Industrial Applications ® Application Note February 12, 2008 AN1384.0 Choice of PWM Controller Target Design Specifications The ISL684x family of devices are superior performing pin compatible replacements for the industry standard 384x single-ended current mode PWM controllers. Also available in 8 Ld MSOP and 8 Ld SOIC, the ISL6841 in the space saving 2mmx3mm DFN package is used in the ISL6841EVAL3Z evaluation board. The following design requirements were targeted for evaluation purposes: • Switching Frequency, fsw: 200kHz. • VIN: 18VDC to 30VDC. • VOUT: 12V with 5% absolute regulation. The design requirements of this application require the superior performance characteristics of the ISL6841. Some key features of this part include: • POUT: 30W. • Tight internal voltage reference of 1%. • Full Load Efficiency: 80% minimum under all line conditions, and loads of 20% and above. • 40ns peak current sensing. • Ripple: 1% of output voltage. • Internal 1A MOSFET driver. • Form Factor: 2”x2”. The ISL6841 was selected for its UVLO threshold and its 50% maximum duty cycle limit. In addition, its low UVLO start threshold would help in easily modifying the design in catering to lower input voltage applications. The detailed design procedure for a continuous mode flyback topology has been discussed in the application note AN1192, available on Intersil’s website: • IOUT: 2.5A. http://www.intersil.com/data/an/an1192.pdf Topology Selection This evaluation board was designed to allow for maximum flexibility, targeting applications that use a typical battery input of 24V. Given the low input voltages for this application, a single-ended topology would be ideal. The flyback topology was selected for the low power levels targeted by this application with emphasis on low BOM cost. Continuous conduction mode of operation was chosen to achieve higher efficiencies at the expense of lower bandwidth of operation, a direct consequence of transition from continuous to discontinuous mode of operation. For feature-rich applications that need short-circuit protection, over-temperature shutdown, etc., the ISL6841 may be substituted with the ISL6721. This evaluation board has been provided with placeholders for primary auxiliary winding feedback to save component cost in case of applications that can tolerate loose regulation requirements. Typical Performance Characteristics The major performance criterion for the converter are efficiency, load regulation and low output ripple. As can be observed from the following figures, the 20% load efficiency target of 80% has been comfortably met under all input voltage conditions. Tight load regulation has been achieved by using the opto-coupled feedback scheme. Waveforms Typical waveforms can be found in the following Figures. Figure 1 shows the efficiency curves at different input voltages. Figure 2 shows the worst case output voltage ripple and noise. Figures 3 through 6 show the drain and gate waveforms of the primary FET under different input and loading conditions. Figures 7 through 10 show the secondary rectifier waveforms under different input and loading conditions. A measure of the stability can be determined from the Bode plots shown in Figures 11 through 14. As shown, the gain and phase margins under the extreme conditions of line and load indicate a stable system under all operating conditions. . 1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2008. All Rights Reserved All other trademarks mentioned are the property of their respective owners. Application Note 1384 100 18V 24V 90 EFFICIENCY (%) 80 70 30V 60 50 40 30 20 10 0 0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 OUTPUT CURRENT 2.00 2.25 2.50 FIGURE 1. EFFICIENCY PLOTS FIGURE 2. OUTPUT RIPPLE AND NOISE, 20MHz BW FIGURE 4. FET VOLTAGES, VIN = 30V, LOAD = 250mA 2 FIGURE 3. FET VOLTAGES, VIN = 18V, LOAD = 250mA FIGURE 5. FET VOLTAGES, VIN = 18V, LOAD = 2.5A AN1384.0 February 12, 2008 Application Note 1384 FIGURE 6. FET VOLTAGES, VIN = 30V, LOAD = 2.5A FIGURE 8. RECTIFIER WAVEFORM, VIN = 30V, LOAD = 250mA FIGURE 7. RECTIFIER WAVEFORM, VIN = 18V, LOAD = 250mA FIGURE 9. RECTIFIER WAVEFORM, VIN = 18V, LOAD = 2.5A FIGURE 10. RECTIFIER WAVEFORM, VIN = 30V, LOAD = 2.5A 3 AN1384.0 February 12, 2008 Application Note 1384 FIGURE 11. STABILITY ANALYSIS, VIN = 18V, FULL LOAD FIGURE 12. STABILITY ANALYSIS, VIN = 18V, NO LOAD 4 AN1384.0 February 12, 2008 Application Note 1384 FIGURE 13. STABILITY ANALYSIS, VIN = 30V, FULL LOAD FIGURE 14. STABILITY ANALYSIS, VIN = 30V, NO LOAD 5 AN1384.0 February 12, 2008 ISL6841EVAL3Z Schematic 6 Application Note 1384 AN1384.0 February 12, 2008 Application Note 1384 . 2.000 Circuit Elements Input Filtering Capacitance – C1, C3 Isolation Transformer – T1 Power MOSFET – Q1 Current Sense Network – T2, D2, R4, R3, C8 (R5 optional) 1.845 Start-up Bias Circuit – R10, Q2, D6 Operating Bias Circuit – D5, R7, C9, D7 Control Circuit – U1, C10, C11, R11, C12, R6 Conventional Rectification Diode – D3 Output Filtering – C5, C6, C2 FIGURE 15. TOP VIEW - ISL6841EVAL3Z BOARD Feedback Network – R13, R14, R15, R16, R17, R18, R19, R20, R21, D8, D9, C15, C16, U2 Slope Compensation - Q3, R22 2.000 Primary RCD Snubber - R1, D1, C4 Primary FET Snubber - R23, C18 Secondary Rectifier Snubber - R2, C7 Safety Capacitor - C17 1.845 Optional Circuit for Primary Auxiliary Feedback - R8, R9, R12, C13, C14 Summary ISL6841 FIGURE 16. BOTTOM VIEW - ISL6841EVAL3Z BOARD 7 Using a high performance, low-cost PWM controller with a low pin-count, all the design targets have been achieved, while keeping the cost to a minimum. The ISL6841EVAL3Z schematic and BOM for the evaluation board are provided as follows. Please contact our Technical Support Center for custom output voltage requirements. They can be reached through Intersil’s website at: http://www.intersil.com/cda/home/ or via phone at 1-888-INTERSIL. AN1384.0 February 12, 2008 Application Note 1384 t Component List REFERENCE DESIGNATOR C1 VENDOR Panasonic PART NUMBER EEE-FK1H151P DESCRIPTION CAP, SMD, 10.3mm, 150µF, 50V, 20%, ROHS, ALUM.ELEC. C2, C6 TDK/Murata CAP, SMD, 1210, 22µF, 16V, 20%, X7R, ROHS C3 TDK/Murata CAP, SMD, 1206, 1µF, 50V, 10%, X7R, ROHS C4 TDK/Murata CAP, SMD, 0805, 0.01µF, 100V, 10%, X7R, ROHS C5 Sanyo 16SVP180M CAP, SMD, E12, 180µF, 16V, 20%, OSCON, ROHS C7, C18 TDK/Murata CAP, SMD, 0805, 820pF, 100V, 5%, NPO, ROHS C8, C12 TDK/Murata CAP, SMD, 0402, 220pF, 50V, 5%, NPO, ROHS C9 TDK/Murata CAP, SMD, 0805,1.0µF, 25V, 10%, X7R, ROHS C10, C11 TDK/Murata CAP, SMD, 0402, 0.1µF, 16V, 10%, X7R, ROHS C15 TDK/Murata CAP, SMD, 0402, 150pF, 50V, 5%, NPO, ROHS C16 TDK/Murata CAP, SMD, 0603, 0.22µF, 16V, 10%, X7R, ROHS C17 Murata GA352QR7GF152KW01L CAP, SMD, 2220, 1500pF, 250V, 10%, X7R, ROHS D1 Diodes B340LB-13-F DIODE-SCHOTTKY, SMD, SMB, 2P, 40V, 3A LOW VF, ROHS D2, D5 Diodes BAS70T-7-F DIODE-SCHOTTKY, SMD, SOT-523, 70V, 70mA, ROHS D3 Diodes PDS560-13 DIODE-RECTIFIER, SMD, POWER DI5, 3P, 60V, 5A, ROHS D6, D9 Diodes BZT52C10T-7 DIODE-ZENER, SMD, SOD-523, 10V, 150mW, ROHS D7 Diodes BAT54CT-7-F DIODE-SCHOTTKY, SMD, SOT-523, 30V, 200mA, DUAL DIODE, ROHS D8 Sipex SPX431LM-L IC-ADJ. PREC.SHUNT REGULATOR, 3P, SOT-23, ROHS Q1 International Rectifier IRF6646 TRANSISTOR-MOS, N-CHANNEL, SMD, DIRECTFET-MN, 80V, 12A, ROHS Q2 Diodes BCX55-16 TRANSISTOR, NPN, SMD, SOT-89, 4P, 60V, 1A, ROHS Q3 On Semi MMBT2222ALT1G-T TRANSISTOR, NPN, 3LD, SOT23, 40V, 600mA, ROHS R1 RES, SMD, 2512, 3.01k, 1W, 1%, TF, ROHS R2, R23 RES, SMD, 2512, 20Ω, 1W, 5%, TF, ROHS R3 RES, SMD, 0402, 249Ω, 1/16W, 1%, TF, ROHS R4 RES-CURR.SENSE, SMD, 1206, 6.49Ω, 1/4W, 1%, ROHS R5 RES, SMD, 2512, 0Ω, 1W, TF, ROHS R6 RES, SMD, 0402, 10Ω, 1/16W, 1%, TF, ROHS R7 RES, SMD, 0402, 100Ω, 1/16W, 1%, TF, ROHS R10 RES, SMD, 0402, 30k, 1/16W, 5%, TF, ROHS R11 RES, SMD, 0402, 17.8k, 1/16W, 1%, TF, ROHS R13, R14 RES, SMD, 0402, 100k, 1/16W, 1%, TF, ROHS R15 RES, SMD, 0402, 5.11k, 1/16W, 1%, TF, ROHS R16 RES, SMD, 0402, 499Ω, 1/16W, 1%, TF, ROHS R17 RES, SMD, 0402, 4.64k, 1/16W, 1%, TF, ROHS R18 RES, SMD, 0402, 1k, 1/16W, 1%, TF, ROHS 8 AN1384.0 February 12, 2008 Application Note 1384 Component List (Continued) REFERENCE DESIGNATOR VENDOR PART NUMBER R19, R22 DESCRIPTION RES, SMD, 0402, 10k, 1/16W, 1%, TF, ROHS R20 RES, SMD, 0402, 6.34k, 1/16W, 1%, TF, ROHS R21 RES, SMD, 0402, 3.83k, 1/16W, 1%, TF, ROHS T1 TDK DCT20EFD-U42S004 TRANSFORMER-FLYBACK, SMD, 20µH, CUSTOM, ROHS T2 Pulse P8205NL TRANSFORMER-CURRENT SENSE, SMD, 8P, 500µH, 10A, ROHS U1 Intersil ISL6841IRZ IC-CURRENT MODE PWM CONTROLLER, 8P, DFN, 2x3, ROHS U2 California Eastern Laboratories PS2801-1-A IC-PHOTOCOUPLER, 4P, SSOP, ROHS 9 AN1384.0 February 12, 2008 Application Note 1384 Layout The ISL6841EVAL3Z board met the form factor target with room to spare. Following are the layout pictures of the board. The gerber files are available upon request. FIGURE 17. SILKSCREEN - TOP LAYER FIGURE 18. SILKSCREEN - BOTTOM LAYER FIGURE 19. ETCH - TOP LAYER FIGURE 20. ETCH - LAYER 2 FIGURE 21. ETCH - LAYER 3 FIGURE 22. ETCH - BOTTOM LAYER Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that the Application Note or Technical Brief is current before proceeding. For information regarding Intersil Corporation and its products, see www.intersil.com 10 AN1384.0 February 12, 2008