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TOP242 Datasheet(PDF) 9 Page - Power Integrations, Inc. |
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TOP242 Datasheet(HTML) 9 Page - Power Integrations, Inc. |
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9 / 48 page  TOP242-249 9 August 8, 2000 E 7/01 DC MAX at higher line voltages helps prevent transformer saturation due to large load transients in forward converter applications. DC MAX of 38% at the OV threshold was chosen to ensure that the power capability of the TOPSwitch-GX is not restricted by this feature under normal operation. Remote ON/OFF and Synchronization TOPSwitch-GX can be turned on or off by controlling the current into the LINE-SENSE pin or out from the EXTERNAL CURRENT LIMIT pin (Y or R package) and into or out from the MULTI-FUNCTION pin (P or G package) (see Figure 11). In addition, the LINE-SENSE pin has a 1 V threshold comparator connected at its input. This voltage threshold can also be used to perform remote ON/OFF control. This allows easy implementation of remote ON/OFF control of TOPSwitch-GX in several different ways. A transistor or an optocoupler output connected between the EXTERNAL CURRENT LIMIT or LINE-SENSE pins (Y or R package) or the MULTI-FUNCTION pin (P or G package) and the SOURCE pin implements this function with “active-on” (Figure 22, 29 and 36) while a transistor or an optocoupler output connected between the LINE-SENSE pin (Y or R package) or the MULTI-FUNCTION (P or G package) pin and the CONTROL pin implements the function with “active-off” (Figure 23 and 37). When a signal is received at the LINE-SENSE pin or the EXTERNAL CURRENT LIMIT pin (Y or R package) or the MULTI-FUNCTION pin (P or G package) to disable the output through any of the pin functions such as OV, UV and remote ON/OFF, TOPSwitch-GX always completes its current switching cycle, as illustrated in Figure 10, before the output is forced off. The internal oscillator is stopped slightly before 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. This approach allows the use of this pin to synchronize TOPSwitch-GX to any external signal with a frequency lower than its internal switching frequency. As seen above, the remote ON/OFF feature allows the TOPSwitch-GX to be turned on and off instantly, on a cycle-by- cycle basis, with very little delay. However, remote ON/OFF can also be used as a standby or power switch to turn off the TOPSwitch-GX and keep it in a very low power consumption state for indefinitely long periods. If the TOPSwitch-GX is held in remote off state for long enough time to allow the CONTROL pin to dishcharge to the internal supply under-voltage threshold of 4.8 V (approximately 32 ms for a 47 µF CONTROL pin capacitance), the CONTROL pin goes into the hysteretic mode of regulation. 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 runs entirely off the high voltage DC input, but with very low power consumption (160 mW typical at 230 VAC with M or X pins open). When the TOPSwitch-GX 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 125 ms for a 47 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 such as inkjet and laser printers. Soft-Start Two on-chip soft-start functions are activated at start-up with a duration of 10 ms (typical). Maximum duty cycle starts from 0% and linearly increases to the default maximum of 78% at the end of the 10 ms duration and the current limit starts from about 85% and linearly increases to 100% at the end of the 10ms duration. In addition to start-up, soft-start is also activated at each restart attempt during auto-restart and when restarting after being in hysteretic regulation of CONTROL pin voltage (V C), due to remote off or thermal shutdown conditions. This effectively minimizes current and voltage stresses on the output MOSFET, the clamp circuit and the output rectifier during start- up. This feature also helps minimize output overshoot and prevents saturation of the transformer during start-up. Shutdown/Auto-Restart To minimize TOPSwitch-GX power dissipation under fault conditions, the shutdown/auto-restart circuit turns the power supply on and off at an auto-restart duty cycle of typically 4% if an out of regulation condition persists. Loss of regulation interrupts the external current into the CONTROL pin. V C regulation changes from shunt mode to the hysteretic auto- restart mode as described in CONTROL pin operation section. When the fault condition is removed, the power supply output becomes regulated, V C regulation returns to shunt mode, and normal operation of the power supply resumes. Hysteretic Over-Temperature Protection Temperature protection is provided by a precision analog circuit that turns the output MOSFET off when the junction temperature exceeds the thermal shutdown temperature (140 °C typical). When the junction temperature cools to below the hysteretic temperature, normal operation resumes providing automatic recovery. A large hysteresis of 70 °C (typical) is provided to prevent overheating of the PC board due to a continuous fault condition. V C is regulated in hysteretic mode and a 4.8 V to 5.8 V (typical) sawtooth waveform is present on the CONTROL pin while in thermal shutdown. Bandgap Reference All critical TOPSwitch-GX internal voltages are derived from a temperature-compensated bandgap reference. This reference is |
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