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TOP254PN Datasheet(PDF) 31 Page - Power Integrations, Inc. |
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TOP254PN Datasheet(HTML) 31 Page - Power Integrations, Inc. |
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31 / 48 page 
Rev. F 01/09 31 TOP252-262 www.powerint.com Quick Design Checklist In order to reduce the no-load input power of TOPSwitch-HX designs, the V-pin (or M-pin for P Package) operates at very low current. This requires careful layout considerations when designing the PCB to avoid noise coupling. Traces and components connected to the V-pin should not be adjacent to any traces carrying switching currents. These include the drain, clamp network, bias winding return or power traces from other converters. If the line sensing features are used, then the sense resistors must be placed within 10 mm of the V-pin to minimize the V pin node area. The DC bus should then be routed to the line sense resistors. Note that external capacitance must not be connected to the V-pin as this may cause misoperaton of the V pin related functions. As with any power supply design, all TOPSwitch-HX designs should be verified on the bench to make sure that components specifications are not exceeded under worst-case conditions. The following minimum set of tests is strongly recommended: Maximum drain voltage – Verify that peak V DS does not exceed 675 V at highest input voltage and maximum overload output power. Maximum overload output power occurs when the output is overloaded to a level just before the power supply goes into auto-restart (loss of regulation). 1. Maximum drain current – At maximum ambient temperature, maximum input voltage and maximum output load, verify drain current waveforms at start-up for any signs of trans- former saturation and excessive leading edge current spikes. TOPSwitch-HX has a leading edge blanking time of 220 ns to prevent premature termination of the ON-cycle. Verify that the leading edge current spike is below the allowed current limit envelope (see Figure 53) for the drain current waveform at the end of the 220 ns blanking period. Thermal check – At maximum output power, both minimum and maximum voltage and ambient temperature; verify that temperature specifications are not exceeded for TOPSwitch-HX, transformer, output diodes and output capacitors. Enough thermal margin should be allowed for the part-to-part variation of the R DS(ON) of TOPSwitch-HX, as specified in the data sheet. The margin required can either be calculated from the values in the parameter table or it can be accounted for by connecting an external resistance in series with the DRAIN pin and attached to the same heat sink, having a resistance value that is equal to the difference between the measured R DS(ON) of the device under test and the worst case maximum specification. Design Tools Up-to-date information on design tools can be found at the Power Integrations website: www.powerint.com 2. 3. Figure 50c. Layout Considerations for TOPSwitch-HX Using L-Package and Operating at 132 kHz. + - DC Out + - HV PI-5216-091508 Y1- Capacitor C7 Isolation Barrier Output Rectifier J1 JP1 C4 R6 D5 C6 R7 VR1 R22 C8 R8 U1 C9 D6 C10 R10 VR2 R9 JP2 R15 R13 R17 U4 C21 R21 D8 C16 R12 HS2 HS1 C17 J2 R20 C19 L3 C18 T1 Output Filter Capacitor Input Filter Capacitor Note: Components U1, R8, C8, C9 and R22 are under heat sink HS1. Transformer X FD Y S C U2 |
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