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DPA424R-TL Datasheet(PDF) 7 Page - Power Integrations, Inc. |
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DPA424R-TL Datasheet(HTML) 7 Page - Power Integrations, Inc. |
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7 / 36 page  DPA423-426 7 K 1/04 will be initiated the next time CONTROL pin voltage reaches 5.8.V. If the power supply loses regulation before reaching the UV lower threshold, the device will enter auto-restart. At the end of each auto-restart cycle (S7), the UV comparator is enabled. If the UV upper threshold is not exceeded the MOSFET will be disabled during the next cycle (see Figure 5). The UV feature can be disabled independent of OV feature. Line Overvoltage Shutdown (OV) The same resistor used for UV also sets an over voltage threshold which, once exceeded, will force the DPA-Switch output into the off-state within one switching cycle. The ratio of OV and UV thresholds is preset at 2.7 as can be seen in Figure 7. When the MOSFET is off, the input voltage surge capability is increased to the voltage rating of the MOSFET (220 V), due to the absence of the reflected voltage and leakage spikes on the drain. A small amount of hysteresis is provided on the OV threshold to prevent noise triggering. The OV feature can be disabled independent of the UV feature as shown in Figure 13. Line Feed Forward with DC MAX Reduction The same resistor used for UV and OV also implements line voltage feed forward that minimizes output line ripple and reduces power supply output sensitivity to line transients. This feed forward operation is illustrated in Figure 4 by the different values of I L. Note that for the same CONTROL pin current, higher line voltage results in smaller operating duty cycle. As an added feature, the maximum duty cycle DC MAX is also reduced from 75% (typical) at a voltage slightly higher than the UV threshold to 33% (typical) at the OV threshold (see Figures 4, 7). Limiting DC MAX at higher line voltages helps prevent transformer saturation due to large load transients in forward converter applications. DC MAX of 33% at the OV threshold was chosen to ensure that the power capability of the DPA-Switch is not restricted by this feature under normal operation. Remote ON/OFF Remote ON/OFF control describes operation where the IC is turned on or off for long periods as opposed to the cycle-by- cycle on/off control which is described in the Synchronization section below. DPA-Switch can be turned on or off by controlling the current into the LINE-SENSE pin or out from the EXTERNAL CURRENT LIMIT pin (see Figure 7). This allows easy implementation of remote ON/OFF control of DPA-Switch in several different ways. A transistor or an optocoupler output connected between the EXTERNAL CURRENT LIMIT pin and the SOURCE pin implements this function with “active- on” (Figures 17, 19 and 21) while a transistor or an optocoupler output connected between the LINE-SENSE pin and the CONTROL pin implements the function with “active-off” (Figures 18, 20 and 22). When a signal is received at the LINE-SENSE pin or the EXTERNAL CURRENT LIMIT pin to disable the output through any of the pin functions such as OV, UV and remote ON/OFF, DPA-Switch always completes its current switching cycle before the output is forced off. The internal oscillator is stopped at the end of the current cycle and stays there as long as the disable signal exists. When the signal at the above pins changes state from disable to enable, the internal oscillator starts the next switching cycle. The remote ON/OFF feature can be used as a standby or power switch to turn off the DPA-Switch and keep it in a very low power consumption state for indefinitely long periods. If the DPA-Switch is held in remote-off state for longer than 10 µs Figure 6. Synchronization Timing Diagram. PI-2762-070501 Oscillator (SAW) D MAX 2 V 0 V V L t ON f SYNC ≥ 128 kHz; t OFF ≤ 7.7 µs; 120 ns ≤ tON ≤ 2250 ns for fOSC = 400 kHz ≤ 3080 ns for fOSC = 300 kHz t OFF ON OFF SYNC Time |
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Similar Description - DPA424R-TL |
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