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DPA424 Datasheet(PDF) 9 Page - Power Integrations, Inc. |
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DPA424 Datasheet(HTML) 9 Page - Power Integrations, Inc. |
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9 / 36 page  Rev. S 12/07 9 DPA422-426 www.powerint.com LINE-SENSE (L) Pin Operation 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 +240 μA (typical). At +240 μA, this pin turns into a constant current sink. Refer to Figure 8. 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 five functions available through the use of the LINE-SENSE pin: OV, UV, line feed-forward with DC MAX reduction, remote ON/OFF and synchronization. Shorting the LINE-SENSE pin to the SOURCE pin disables all five functions. The LINE-SENSE pin is typically used for line sensing by connecting a resistor from this pin to the positive input DC voltage bus to implement OV, UV and line feed-forward with DC MAX reduction over line voltage. In this mode, the value of the resistor determines the line OV/UV thresholds, and the DC MAX is reduced linearly with input DC high voltage starting from just above the UV threshold. This pin can also be used as the input pin for remote ON/OFF and synchronization. An external transistor placed between the LINE-SENSE pin and the CONTROL pin realizes remote ON/OFF via UV or OV threshold. Synchronization is available by connecting an open drain external MOSFET between the LINE-SENSE pin and the SOURCE pin to generate synchronization pulse. Each time the MOSFET turns on, the falling edge of the LINE-SENSE pin voltage initiates a new switching cycle. The lowest synchronization frequency guaranteed by DPA-Switch is 128 kHz. Refer to Table 2 for possible combinations of the functions with example circuits shown in Figure 11 through Figure 24. A description of specific functions in terms of the LINE-SENSE pin I/V characteristic is shown in Figure 7 (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 4 μA hysteresis) and OV triggers at I OV (+135 μA typical with 4 μA hysteresis). Between the UV and OV thresholds, 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 75% at I L(DC) (+55 μA typical) to 33% at I OV (+135 μA). EXTERNAL CURRENT LIMIT (X) Pin Operation 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 -230 μA (typical). At -230 μA, it turns into a constant current source (refer to Figure 8). There are two functions available through the use of the EXTERNAL CURRENT LIMIT pin: external current limit and remote ON/OFF. Shorting the EXTERNAL CURRENT LIMIT pin and SOURCE pin disables both 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 control input. Table 2 shows several different ways of using this pin. See Figure 7 for a description of the functions where the horizontal axis (left hand side) represents the EXTERNAL CURRENT LIMIT pin current. The meaning of the vertical axes varies with function. For those that control the on/off states of the output such as remote ON/OFF, the vertical axis represents the enable/ disable states of the output. For external current limit, the vertical axis represents the magnitude of the I LIMIT. Please see graphs in the Typical Performance Characteristics section for the current limit programming range and the selection of the appropriate resistor value. |
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