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DPA424 Datasheet(PDF) 7 Page - Power Integrations, Inc. |
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DPA424 Datasheet(HTML) 7 Page - Power Integrations, Inc. |
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7 / 36 page  Rev. S 12/07 7 DPA422-426 www.powerint.com Figure 6. Synchronization Timing Diagram. (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 (typical), the CONTROL pin goes into the hysteretic mode of operation. In this mode, the CONTROL pin goes through alternate charge and discharge cycles between 4.8 V and 5.8 V (see CONTROL Pin Operation section above) and the IC runs entirely off the high voltage DC input, but with very low power consumption (30 mW typical at 48 V with LINE-SENSE and EXTERNAL CURRENT LIMIT pins open). When the DPA-Switch is remotely turned on after entering this mode, it will initiate a normal start-up sequence with soft-start the next time the CONTROL pin reaches 5.8 V. In the worst case, the delay from remote on to start-up can be equal to the full discharge/charge cycle time of the CONTROL pin, which is approximately 36 ms for a 22 μF CONTROL pin capacitor. This reduced- consumption remote-off mode can eliminate expensive and unreliable in-line mechanical switches. It also allows for microprocessor-controlled turn-on and turn-off sequences that may be required in certain applications. Synchronization In addition to sensing incoming current for OV, UV and remote ON/OFF, the LINE-SENSE pin also monitors its pin voltage through a 1 V threshold comparator. A pin voltage below 1 V turns on DPA-Switch. When the voltage at LINE-SENSE pin rises beyond 1 V to disable the output, DPA-Switch completes its current switching cycle before the output is forced off (similar to remote ON/OFF operation). The internal oscillator is stopped at the end of the current cycle awaiting the LINE-SENSE pin voltage to go low to start the next cycle. This allows the use of the 1 V threshold to synchronize DPA-Switch to an external signal with a frequency lower than its internal switching frequency. A transistor or an optocoupler output connected between the LINE-SENSE pin and the SOURCE pin implements this function (see Figure 24). Please refer to Figure 6 for the timing waveforms of synchronization operation. 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 ≤ t ON ≤ 2250 ns for fOSC = 400 kHz ≤ 3080 ns for f OSC = 300 kHz t OFF ON OFF SYNC Time |
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