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TOP226Y Datasheet(PDF) 8 Page - Power Integrations, Inc. |
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TOP226Y Datasheet(HTML) 8 Page - Power Integrations, Inc. |
8 / 21 page TOP221-227 D 7/01 8 Key Application Considerations General Guidelines • Keep the SOURCE pin length very short. Use a Kelvin connection to the SOURCE pin for the CONTROL pin bypass capacitor. Use single point grounding techniques at the SOURCE pin as shown in Figure 9. • Minimize peak voltage and ringing on the DRAIN voltage at turn-off. Use a Zener or TVS Zener diode to clamp the drain voltage below the breakdown voltage rating of TOPSwitch under all conditions, including start-up and overload. The maximum recommended clamp Zener voltage for the TOP2XX series is 200 V and the corresponding maximum reflected output voltage on the primary is 135 V. Please see Step 4: AN-16 in the 1996-97 Data Book and Design Guide or on our Web site. • The transformer should be designed such that the rate of change of drain current due to transformer saturation is within the absolute maximum specification ( ∆I D in 100 ns before turn off as shown in Figure 13). As a guideline, for most common transformer cores, this can be achieved by maintaining the Peak Flux Density (at maximum I LIMIT current) below 4200 Gauss (420 mT). The transformer spreadsheets Rev. 2.1 (or later) for continuous and Rev.1.0 (or later) for discontinuous conduction mode provide the necessary information. • Do not plug TOPSwitch into a “hot” IC socket during test. External CONTROL pin capacitance may be charged to excessive voltage and cause TOPSwitch damage. • While performing TOPSwitch device tests, do not exceed maximum CONTROL pin voltage of 9 V or maximum CONTROL pin current of 100 mA. • Under some conditions, externally provided bias or supply current driven into the CONTROL pin can hold the TOPSwitch in one of the 8 auto-restart cycles indefinitely and prevent starting. To avoid this problem when doing bench evaluations, it is recommended that the V C power supply be turned on before the DRAIN voltage is applied. TOPSwitch can also be reset by shorting the CONTROL pin to the SOURCE pin momentarily. • CONTROL pin currents during auto-restart operation are much lower at low input voltages (< 36 V) which increases the auto-restart cycle time (see the I C vs. DRAIN Voltage Characteristic curve). • Short interruptions of AC power may cause TOPSwitch to enter the 8-count auto-restart cycle before starting again. This is because the input energy storage capacitors are not completely discharged and the CONTROL pin capacitance has not discharged below the internal power-up reset voltage. • In some cases, minimum loading may be necessary to keep a lightly loaded or unloaded output voltage within the desired range due to the minimum ON-time. ReplacingTOPSwitch with TOPSwitch-II There is no external latching shutdown function in TOPSwitch-II. Otherwise, the functionality of the TOPSwitch-II devices is same as that of the TOPSwitch family. However, before considering TOPSwitch-II as a 'drop in' replacement in an existing TOPSwitch design, the design should be verified as described below. The new TOPSwitch-II family offers more power capability than the original TOPSwitch family for the same MOSFET R DS(ON). Therefore, the original TOPSwitch design must be reviewed to make sure that the selected TOPSwitch-II replacement device and other primary components are not over stressed under abnormal conditions. The following verification steps are recommended: • Check the transformer design to make sure that it meets the ∆I D specification as outlined in the General Guidelines section above. • Thermal: Higher power capability of the TOPSwitch-II would in many instances allow use of a smaller MOSFET device (higher R DS(ON)) for reduced cost. This may affect TOPSwitch power dissipation and power supply efficiency. Therefore thermal performance of the power supply must be verified with the selected TOPSwitch-II device. • Clamp Voltage: Reflected and Clamp voltages should be verified not to exceed recommended maximums for the TOP2XX Series: 135 V Reflected/200 V Clamp. Please see Step 4: AN-16 in the Data Book and Design Guide and readme.txt file attached to the transformer design spreadsheets. • Agency Approval: Migrating to TOPSwitch-II may require agency re-approval. |
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