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TOP242F Datasheet(PDF) 11 Page - Power Integrations, Inc. |
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TOP242F Datasheet(HTML) 11 Page - Power Integrations, Inc. |
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11 / 52 page  TOP242-250 11 G 1/02 FREQUENCY (F) Pin Operation The FREQUENCY pin is a digital input pin available in the Y, R or F package only. Shorting the FREQUENCY pin to SOURCE pin selects the nominal switching frequency of 132 kHz (Figure 13) which is suited for most applications. For other cases that may benefit from lower switching frequency such as noise sensitive video applications, a 66 kHz switching frequency (half frequency) can be selected by shorting the FREQUENCY pin to the CONTROL pin (Figure 14). In addition, an example circuit shown in Figure 15 may be used to lower the switching frequency from 132 kHz in normal operation to 66 kHz in standby mode for very low standby power consumption. LINE-SENSE (L) Pin Operation (Y, R and F Packages) When current is fed into the LINE-SENSE pin, it works as a voltage source of approximately 2.6 V up to a maximum current of +400 µA (typical). At +400 µA, this pin turns into a constant current sink. Refer to Figure 12a. In addition, a comparator with a threshold of 1 V is connected at the pin and is used to detect when the pin is shorted to the SOURCE pin. There are a total of four functions available through the use of the LINE-SENSE pin: OV, UV, line feed forward with DC MAX reduction, and remote ON/OFF. Connecting the LINE-SENSE pin to the SOURCE pin disables all four functions. The LINE- SENSE pin is typically used for line sensing by connecting a resistor from this pin to the rectified DC high voltage bus to imple- ment OV, UV and DC MAX reduction with line voltage. In this mode, the value of the resistor determines the line OV/UV thresh- olds, and the DC MAX is reduced linearly with rectified DC high voltage starting from just above the UV threshold. The pin can also be used as a remote on/off and a synchronization input. Refer to Table 2 for possible combinations of the functions with Using Feature Pins ✔ ✔✔ ✔ ✔ ✔ ✔✔ ✔ ✔ ✔ ✔✔ ✔ ✔ ✔ ✔✔ ✔ ✔ ✔✔ ✔✔ ✔ ✔ ✔✔ ✔ 16 17 18 19 20 21 22 23 24 25 26 27 28 29 Table 2. Typical LINE-SENSE and EXTERNAL CURRENT LIMIT Pin Configurations. *This table is only a partial list of many LINE-SENSE and EXTERNAL CURRENT LIMIT pin configurations that are possible. Figure Number Three Terminal Operation Under-Voltage Overvoltage Line Feed Forward (DC MAX) Overload Power Limiting External Current Limit Remote ON/OFF example circuits shown in Figure 16 through Figure 40. A description of specific functions in terms of the LINE-SENSE pin I/V characteristic is shown in Figure 11 (right hand side). The horizontal axis represents LINE-SENSE pin current with positive polarity indicating currents flowing into the pin. The meaning of the vertical axes varies with functions. For those that control the on/off states of the output such as UV, OV and remote ON/OFF, the vertical axis represents the enable/ disable states of the output. UV triggers at I UV (+50 µA typical with 30 µA hysteresis) and OV triggers at I OV (+225 µA typical with 8 µA hysteresis). Between the UV and OV thresh- olds, the output is enabled. For line feed forward with DC MAX reduction, the vertical axis represents the magnitude of the DC MAX. Line feed forward with DCMAX reduction lowers maximum duty cycle from 78% at I L(DC) (+60 µA typical) to 38% at I OV (+225 µA). EXTERNAL CURRENT LIMIT (X) Pin Operation (Y, R and F Packages) When current is drawn out of the EXTERNAL CURRENT LIMIT pin, it works as a voltage source of approximately 1.3 V up to a maximum current of –240 µA (typical). At –240 µA, it turns into a constant current source (refer to Figure 12a). There are two functions available through the use of the EXTERNAL CURRENT LIMIT pin: external current limit and remote ON/OFF. Connecting the EXTERNAL CURRENT LIMIT pin and SOURCE pin disables the two functions. In high efficiency applications this pin can be used to reduce the current limit externally to a value close to the operating peak current, by connecting the pin to the SOURCE pin through a resistor. The pin can also be used as a remote on/off. Table 2 shows several possible combinations using this pin. See LINE-SENSE AND EXTERNAL CURRENT LIMIT PIN TABLE* |
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