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TOP257EN Datasheet(PDF) 11 Page - Power Integrations, Inc. |
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TOP257EN Datasheet(HTML) 11 Page - Power Integrations, Inc. |
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11 / 49 page  Rev. F 01/09 11 TOP252-262 www.powerint.com Line Overvoltage Shutdown (OV) The same resistor used for UV also sets an overvoltage threshold, which, once exceeded, will force TOPSwitch-HX to stop switching instantaneously (after completion of the current switching cycle). If this condition lasts for at least 100 μs, the TOPSwitch-HX output will be forced into off state. Unlike with TOPSwitch-GX, however, when the line voltage is back to normal with a small amount of hysteresis provided on the OV threshold to prevent noise triggering, the state machine sets to S13 and forces TOPSwitch-HX to go through the entire auto- restart sequence before attempting to switch again. The ratio of OV and UV thresholds is preset at 4.5, as can be seen in Figure 12. When the MOSFET is off, the rectified DC high voltage surge capability is increased to the voltage rating of the MOSFET (700 V), due to the absence of the reflected voltage and leakage spikes on the drain. The OV feature can be disabled independent of the UV feature. 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 currents. 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. Hysteretic or Latching Output Overvoltage Protection (OVP) The detection of the hysteretic or latching output overvoltage protection (OVP) is through the trigger of the line overvoltage threshold. The V-pin or M-pin voltage will drop by 0.5 V, and the controller measures the external attached impedance immediately after this voltage drops. If I V or IM exceeds IOV(LS) (336 μA typical) longer than 100 μs, TOPSwitch-HX will latch into a permanent off state for the latching OVP. It only can be reset if V V or VM goes below 1 V or VC goes below the power- up-reset threshold (V C(RESET)) and then back to normal. If I V or IM does not exceed IOV(LS) or exceeds no longer than 100 μs, TOPSwitch-HX will initiate the line overvoltage and the hysteretic OVP. Their behavior will be identical to the line overvoltage shutdown (OV) that has been described in detail in the previous section. Voltage Monitor and External Current Limit Pin Table* Figure Number 16 17 18 19 20 21 22 23 24 25 26 27 28 Three Terminal Operation ✓ Line Undervoltage ✓✓✓✓ ✓✓ Line Overvoltage ✓✓✓ ✓ ✓✓ Line Feed-Forward (DC MAX) ✓✓✓ ✓✓ Output Overvoltage Protection ✓✓ Overload Power Limiting ✓ External Current Limit ✓✓ ✓✓✓ Remote ON/OFF ✓✓✓ Device Reset ✓ *This table is only a partial list of many VOLTAGE MONITOR and EXTERNAL CURRENT LIMIT Pin Configurations that are possible. Table 2. VOLTAGE MONITOR (V) Pin and EXTERNAL CURRENT LIMIT (X) Pin Configuration Options. Multi-Function Pin Table* Figure Number 29 30 31 32 33 34 35 36 37 38 39 40 Three Terminal Operation ✓ Line Undervoltage ✓✓✓✓ Line Overvoltage ✓✓✓ ✓ Line Feed-Forward (DC MAX) ✓✓✓ Output Overvoltage Protection ✓✓ Overload Power Limiting ✓ External Current Limit ✓✓ ✓✓ Remote ON/OFF ✓✓✓ Device Reset ✓ *This table is only a partial list of many MULTI-FUNCTIONAL Pin Configurations that are possible. Table 3. MULTI-FUNCTION (M) Pin Configuration Options. |
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