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TOP233G Datasheet(PDF) 8 Page - Power Analog Micoelectronics |
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TOP233G Datasheet(HTML) 8 Page - Power Analog Micoelectronics |
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8 / 36 page  TOP232-234 8 B 7/01 As seen above, the remote ON/OFF feature allows the TOPSwitch-FX 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-FX and keep it in a very low power consumption state for indefinitely long periods. If the TOPSwitch-FX 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 pin open). When the TOPSwitch-FX 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. See Figure 27 under application examples for more information. Soft-Start An on-chip soft-start function is activated at start-up with a duration of 10 ms (typical). Maximum duty cycle starts from zero and linearly increases to the default maximum of 78% at the end of the 10 ms 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-FX 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 described above. 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 (135 ˚C typical). When the junction temperature cools to below the hysteretic temperature, normal operation resumes. A large hysteresis of 70 ˚C (typical) is provided to prevent overheating of the PC board due to a repeating 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 when the power supply is turned off. Bandgap Reference All critical TOPSwitch-FX internal voltages are derived from a temperature-compensated bandgap reference. This reference is also used to generate a temperature-compensated current reference which is trimmed to accurately set the switching frequency, MOSFET gate drive current, current limit, and the line OV/UV thresholds. TOPSwitch-FX has improved circuitry to maintain all of the above critical parameters within very tight absolute and temperature tolerances. High-Voltage Bias Current Source This current source biases TOPSwitch-FX from the DRAIN pin and charges the CONTROL pin external capacitance during start-up or hysteretic operation. Hysteretic operation occurs during auto-restart, remote off and over-temperature shutdown. In this mode of operation, the current source is switched on and off with an effective duty cycle of approximately 35%. This duty cycle is determined by the ratio of CONTROL pin charge (I C) and discharge currents (ICD1 and ICD2). This current source is turned off during normal operation when the output MOSFET is switching. |
Similar Part No. - TOP233G |
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Similar Description - TOP233G |
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