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TNY268G Datasheet(PDF) 11 Page - Power Integrations, Inc. |
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TNY268G Datasheet(HTML) 11 Page - Power Integrations, Inc. |
11 / 22 page Rev. H 02/09 11 TNY263-268 www.powerint.com core size and design (continuous or discontinuous), efficiency, minimum specified input voltage, input storage capacitance, output voltage, output diode forward drop, etc., and can be different from the values shown in Table 1. Audible Noise The TinySwitch-II practically eliminates any transformer audio noise using simple ordinary varnished transformer construction. No gluing of the cores is needed. The audio noise reduction is accomplished by the TinySwitch-II controller reducing the current limit in discrete steps as the load is reduced. This minimizes the flux density in the transformer when switching at audio frequencies. Worst Case EMI & Efficiency Measurement Since identical TinySwitch-II supplies may operate at several different frequencies under the same load and line conditions, care must be taken to ensure that measurements are made under worst case conditions. When measuring efficiency or EMI verify that the TinySwitch-II is operating at maximum frequency and that measurements are made at both low and high line input voltages to ensure the worst case result is obtained. Layout Single Point Grounding Use a single point ground connection at the SOURCE pin for the BYPASS pin capacitor and the Input Filter Capacitor (see Figure 17). Primary Loop Area The area of the primary loop that connects the input filter capacitor, transformer primary and TinySwitch-II together should be kept as small as possible. Primary Clamp Circuit A clamp is used to limit peak voltage on the DRAIN pin at turn- off. This can be achieved by using an RCD clamp (as shown in Figure 14). A Zener and diode clamp (200 V) across the primary or a single 550 V Zener clamp from DRAIN to SOURCE can also be used. In all cases care should be taken to minimize the circuit path from the clamp components to the transformer and TinySwitch-II. Thermal Considerations Copper underneath the TinySwitch-II acts not only as a single point ground, but also as a heatsink. The hatched areas shown in Figure 17 should be maximized for good heat sinking of TinySwitch-II and the same applies to the output diode. EN/UV pin If a line undervoltage detect resistor is used then the resistor should be mounted as close as possible to the EN/UV pin to minimize noise pick up. The voltage rating of a resistor should be considered for the undervoltage detect (Figure 15: R2, R3) resistors. For 1/4 W resistors, the voltage rating is typically 200 V continuous, whereas for 1/2 W resistors the rating is typically 400 V continuous. Y-Capacitor The placement of the Y-capacitor should be directly from the primary bulk capacitor positive rail to the common/return terminal on the secondary side. Such placement will maximize the EMI benefit of the Y-capacitor and avoid problems in common-mode surge testing. Optocoupler It is important to maintain the minimum circuit path from the optocoupler transistor to the TinySwitch-II EN/UV and SOURCE pins to minimize noise coupling. The EN/UV pin connection to the optocoupler should be kept to an absolute minimum (less than 12.7 mm or 0.5 in.), and this connection should be kept away from the DRAIN pin (minimum of 5.1 mm or 0.2 in.). Output Diode For best performance, the area of the loop connecting the secondary winding, the output diode and the output filter capacitor, should be minimized. See Figure 17 for optimized layout. In addition, sufficient copper area should be provided at the anode and cathode terminals of the diode for adequate heatsinking. Input and Output Filter Capacitors There are constrictions in the traces connected to the input and output filter capacitors. These constrictions are present for two reasons. The first is to force all the high frequency currents to flow through the capacitor (if the trace were wide then it could flow around the capacitor). Secondly, the Constrictions minimize the heat transferred from the TinySwitch-II to the input filter capacitor and from the secondary diode to the output filter capacitor. The common/return (the negative output terminal in Figure 17) terminal of the output filter capacitor should be connected with a short, low impedance path to the secondary winding. In addition, the common/ return output connection should be taken directly from the secondary winding pin and not from the Y-capacitor connection point. PC Board Cleaning Power Integrations does not recommend the use of “no clean” flux. For the most up-to-date information visit the PI website at: www.powerint.com. |
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