Datasheet TOP242, TOP243, TOP244, TOP245, TOP246, TOP247, TOP248, TOP249, TOP250 (Power Integrations) - 6

TOP242-250
66 kHz can be chosen by connecting this pin to CONTROL pin voltage has had a chance to discharge to the lower pin instead. Leaving this pin open is not recommended. threshold voltage of approximately 4.8 V (internal supply undervoltage lockout threshold). When the externally fed
CONTROL (C) Pin Operation
current charges the CONTROL pin to the shunt regulator The CONTROL pin is a low impedance node that is capable voltage of 5.8 V, current in excess of the consumption of of receiving a combined supply and feedback current. During the chip is shunted to SOURCE through resistor R as normal operation, a shunt regulator is used to separate E shown in Figure 2. This current flowing through R controls the feedback signal from the supply current. CONTROL E the duty cycle of the power MOSFET to provide closed pin voltage V is the supply voltage for the control circuitry C loop regulation. The shunt regulator has a finite low output including the MOSFET gate driver. An external bypass impedance Z that sets the gain of the error amplifier when capacitor closely connected between the CONTROL and C used in a primary feedback configuration. The dynamic SOURCE pins is required to supply the instantaneous gate impedance Z of the CONTROL pin together with the drive current. The total amount of capacitance connected C external CONTROL pin capacitance sets the dominant pole to this pin also sets the auto-restart timing as well as for the control loop. control loop compensation. When a fault condition such as an open loop or shorted When rectified DC high voltage is applied to the DRAIN pin output prevents the flow of an external current into during start-up, the MOSFET is initially off, and the CONTROL the CONTROL pin, the capacitor on the CONTROL pin capacitor is charged through a switched high voltage pin discharges towards 4.8 V. At 4.8 V, auto-restart is current source connected internally between the DRAIN activated which turns the output MOSFET off and puts and CONTROL pins. When the CONTROL pin voltage the control circuitry in a low current standby mode. The V reaches approximately 5.8 V, the control circuitry is high-voltage current source turns on and charges the C activated and the soft-start begins. The soft-start circuit external capacitance again. A hysteretic internal supply gradually increases the duty cycle of the MOSFET from undervoltage comparator keeps V within a window C zero to the maximum value over approximately 10 ms. If no of typically 4.8 V to 5.8 V by turning the high-voltage external feedback/supply current is fed into the CONTROL current source on and off as shown in Figure 8. The pin by the end of the soft-start, the high voltage current auto-restart circuit has a divide-by-eight counter which source is turned off and the CONTROL pin will start prevents the output MOSFET from turning on again until discharging in response to the supply current drawn by the eight discharge/charge cycles have elapsed. This is control circuitry. If the power supply is designed properly, accomplished by enabling the output MOSFET only when and no fault condition such as open loop or shorted the divide-by-eight counter reaches full count (S7). The output exists, the feedback loop will close, providing counter effectively limits TOPSwitch-GX power dissipation external CONTROL pin current, before the CONTROL by reducing the auto-restart duty cycle to typically 4%. ~ ~ ~ ~
VUV V
~ ~ ~ ~ ~ ~
LINE 0 V S7 S0 S1 S2 S6 S7 S0 S1 S2 S6 S7 S0 S1 S2 S6 S7 S7 5.8 V V
~ ~ ~ ~ ~ ~
4.8 V C 0 V
~ ~ ~ ~
VDRAIN
~ ~
0 V VOUT 0 V
~ ~ ~ ~ ~ ~ 1 2 3 2 4
Note: S0 through S7 are the output states of the auto-restart counter
PI-2545-082299 Figure 8. Typical Waveforms for (1) Power Up (2) Normal Operation (3) Auto-Restart (4) Power Down.
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