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TOP221Y Datasheet(PDF) 5 Page - Power Integrations, Inc. |
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TOP221Y Datasheet(HTML) 5 Page - Power Integrations, Inc. |
5 / 20 page C 12/97 TOP221-227 5 PI-2030-042397 VIN VOUT 0 IOUT 0 1 2 1 3 1 DRAIN 0 VIN VC 0 ••• ••• 12 12 81 0 IC ••• ••• 12 8 81 2 8 1 VC(reset) the output MOSFET off until the start of the next clock cycle. The current limit comparator threshold voltage is temperature compensated to minimize variation of the effective peak current limit due to temperature related changes in output MOSFET R DS(ON). The leading edge blanking circuit inhibits the current limit comparator for a short time after the output MOSFET is turned on. The leading edge blanking time has been set so that current spikes caused by primary-side capacitances and secondary-side rectifier reverse recovery time will not cause premature termination of the switching pulse. The current limit can be lower for a short period after the leading edge blanking time as shown in Figure 12. This is due to dynamic characteristics of the MOSFET. To avoid triggering the current limit in normal operation, the drain current waveform should stay within the envelope shown. Shutdown/Auto-restart To minimize TOPSwitch power dissipation, the shutdown/ auto-restart circuit turns the power supply on and off at an auto- restart duty cycle of typically 5% 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. Overtemperature 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 (typically 135 °C). Activating the power-up reset circuit by removing and restoring input power or momentarily pulling the CONTROL pin below the power-up reset threshold resets the latch and allows TOPSwitch to resume normal power supply operation. V C is regulated in hysteretic mode and a 4.7 V to 5.7 V (typical) sawtooth waveform is present on the CONTROL pin when the power supply is latched off. High-voltage Bias Current Source This current source biases TOPSwitch from the DRAIN pin and charges the CONTROL pin external capacitance (C T) during start-up or hysteretic operation. Hysteretic operation occurs during auto-restart and overtemperature latched shutdown. 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 (I CD1 and ICD2). This current source is turned off during normal operation when the output MOSFET is switching. Figure 6. Typical Waveforms for (1) Normal Operation, (2) Auto-restart, and (3) Power Down Reset. |
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