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TOP248G- Datasheet(PDF) 10 Page - Power Integrations, Inc. |
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TOP248G- Datasheet(HTML) 10 Page - Power Integrations, Inc. |
10 / 52 page TOP242-250 M 12/04 10 Table 2. Typical LINE-SENSE and EXTERNAL CURRENT LIMIT Pin Configurations. Bandgap Reference All critical TOPSwitch-GX internal voltages are derived from a temperature-compensated bandgap reference. This reference is also used to generate a temperature-compensated current reference, which is trimmed to accurately set the switching frequency, MOSFET gate drive current, current limit, and the lineOV/UVthresholds. TOPSwitch-GXhasimprovedcircuitry to maintain all of the above critical parameters within very tight absolute and temperature tolerances. High-Voltage Bias Current Source This current source biases TOPSwitch-GX from the DRAIN pin and charges the CONTROL pin external capacitance during start-up or hysteretic operation. Hysteretic operation occurs during auto-restart, remote OFF and over-temperature shutdown. In this mode of operation, 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. The effect of the current source switching will be seen on the DRAIN voltage waveform as small disturbances and is normal. Using Feature Pins 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 implement OV, UV and DC MAX reduction with line voltage. In this mode, the value of the resistor determines the line OV/UV thresholds, and the DC MAX is reduced linearly with rectified DC high voltage starting from just above the UVthreshold. The pin can also be used as a remote ON/OFF and a synchronization input. RefertoTable2forpossiblecombinationsofthefunctions with 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 thresholds, the output is enabled. For line feed-forward with LINE-SENSE AND EXTERNAL CURRENT LIMIT PIN TABLE* Figure Number 16 17 18 19 20 21 22 23 24 25 26 27 28 29 Three Terminal Operation ✓ Under-Voltage ✓ ✓ ✓ ✓ ✓ Overvoltage ✓ ✓ ✓ ✓ ✓ Line Feed-Forward (DC MAX) ✓ ✓ ✓ ✓ Overload Power Limiting ✓ External Current Limit ✓ ✓ ✓ ✓ ✓ ✓ Remote ON/OFF ✓ ✓ ✓ ✓ ✓ ✓ ✓ *This table is only a partial list of many LINE-SENSE and EXTERNAL CURRENT LIMIT pin configurations that are possible. |
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