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TOP233G Datasheet(PDF) 4 Page - Power Integrations, Inc. |
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TOP233G Datasheet(HTML) 4 Page - Power Integrations, Inc. |
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4 / 36 page  TOP232-234 4 B 7/01 TOPSwitch-FX Family Functional Description Figure 4. Relationship of Duty Cycle to CONTROL Pin Current. PI-2504-072799 I C (mA) I M = 140 µA I M = 190 µA I M < I M(DC) 1.9 1.5 5.5 5.9 Slope = PWM Gain I CD1 I B Auto-restart 78 1.5 47 Like TOPSwitch, TOPSwitch-FX is an integrated switched mode power supply chip that converts a current at the control input to a duty cycle at the open drain output of a high voltage power MOSFET. During normal operation the duty cycle of the power MOSFET decreases linearly with increasing CONTROL pin current as shown in Figure 4. In addition to the three terminal TOPSwitch features, such as the high voltage start-up, the cycle-by-cycle current limiting, loop compensation circuitry, auto-restart, thermal shutdown, etc., the TOPSwitch-FX incorporates many additional functions that reduce system cost, increase power supply performance and design flexibility. A patented high voltage CMOS technology allows both the high voltage power MOSFET and all the low voltage control circuitry to be cost effectively integrated onto a single monolithic chip. Two terminals, FREQUENCY (available only in Y package) and MULTI-FUNCTION, have been added to implement some of the new functions. These terminals can be connected to the SOURCE pin to operate the TOPSwitch-FX in a TOPSwitch- like three terminal mode. However, even in this three terminal mode, the TOPSwitch-FX offers many new transparent features that do not require any external components: 1. A fully integrated 10 ms soft-start reduces peak currents and voltages during start-up and practically eliminates output overshoot in most applications. 2. DC MAX of 78% allows smaller input storage capacitor, lower input voltage requirement and/or higher power capability. 3. Cycle skipping at minimum pulse width achieves regulation and very low power consumption at no load. 4. Higher switching frequency of 132 kHz reduces the transformer size with no noticeable impact on EMI or on high line efficiency. 5. Frequency jittering reduces EMI. 6. Hysteretic over-temperature shutdown ensures automatic recovery from thermal fault. Large hysteresis prevents circuit board overheating. 7. Packages with omitted pins and lead forming provide large DRAIN creepage distance. 8. Tighter absolute tolerances and smaller temperature vari- ations on switching frequency, current limit and PWM gain. The MULTI-FUNCTION pin is usually used for line sensing by connecting a resistor from this pin to the rectified DC high voltage bus to implement line over-voltage (OV)/under-voltage (UV) and line feed forward with DC MAX reduction. In this mode, the value of the resistor determines the OV/UV thresholds and the DC MAX is reduced linearly starting from a line voltage above the under-voltage threshold. In high efficiency applications, this pin can be used in the external current limit mode instead, to reduce the current limit externally (to a value close to the operating peak current), by connecting the pin to SOURCE through a resistor. The same pin can also be used as a remote ON/OFF and a synchronization input in both modes. The FREQUENCY pin in the TO-220 package sets the switching frequency to the default value of 132 kHz when connected to SOURCE pin. A half frequency option can be chosen by connecting this pin to CONTROL pin instead. Leaving this pin open is not recommended. CONTROL (C) Pin Operation The CONTROL pin is a low impedance node that is capable of receiving a combined supply and feedback current. During normal operation, a shunt regulator is used to separate the feedback signal from the supply current. CONTROL pin voltage V C is the supply voltage for the control circuitry including the MOSFET gate driver. An external bypass capacitor closely connected between the CONTROL and SOURCE pins is required to supply the instantaneous gate drive current. The total amount of capacitance connected to this pin also sets the auto-restart timing as well as control loop compensation. When rectified DC high voltage is applied to the DRAIN pin during start-up, the MOSFET is initially off, and the CONTROL pin capacitor is charged through a switched high voltage current source connected internally between the DRAIN and CONTROL pins. When the CONTROL pin voltage V C reaches approximately 5.8 V, the control circuitry is activated and the soft-start begins. The soft-start circuit gradually increases the duty cycle of the MOSFET from zero to the maximum value over approximately 10 ms. If no external feedback/supply current is fed into the CONTROL pin by the end of the soft-start, the high voltage current source is turned off and the CONTROL pin will start discharging in response to the supply current drawn by the control circuitry. If the power supply is designed properly, and no fault condition such as open loop or shorted output exists, the feedback loop will close, providing external |
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