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TOP264-271 Datasheet(PDF) 8 Page - Power Integrations, Inc. |
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TOP264-271 Datasheet(HTML) 8 Page - Power Integrations, Inc. |
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8 / 40 page  Rev. E 08/12 8 TOP264-271 www.powerint.com If the power supply is operating under heavy load or low input line conditions when an open-loop occurs, the output voltage may not rise significantly. Under these conditions, a latching shutdown will not occur until load or line conditions change. Nevertheless, the operation provides the desired protection by preventing significant rise in the output voltage when the line or load conditions do change. Primary-side OVP protection with the TOP264-271 in a typical application will prevent a nominal 12 V output from rising above approximately 20 V under open- loop conditions. If greater accuracy is required, a secondary sensed OVP circuit is recommended. Line Feed-Forward with DC MAX Reduction The same resistor used for UV and OV also implements line voltage feed-forward, which minimizes output line ripple and reduces power supply output sensitivity to line transients. Note that for the same CONTROL pin current, higher line voltage results in smaller operating duty cycle. As an added feature, the maximum duty cycle DC MAX is also reduced from 78% (typical) at a voltage slightly lower than the UV threshold to 36% (typical) at the OV threshold. DC MAX of 36% at high-line was chosen to ensure that the power capability of the TOP264-271 is not restricted by this feature under normal operation. TOP264-271 provides a better fit to the ideal feed-forward by using two reduction slopes: -1% per mA for all bus voltage less than 195 V (typical for 4 M W line impedance) and -0.25% per mA for all bus voltage more than 195 V. Remote-ON/OFF TOP264-271 can be turned on or off by controlling the current into the VOLTAGE-MONITOR pin or out from the EXTERNAL CURRENT LIMIT pin. In addition, the VOLTAGE-MONITOR pin has a 1 V threshold comparator connected at its input. This voltage threshold can also be used to perform remote-ON/OFF control. When a signal is received at the VOLTAGE-MONITOR pin or the EXTERNAL CURRENT LIMIT pin to disable the output through any of the pin functions such as OV, UV and remote-ON/OFF, TOP264-271 always completes its current switching cycle before the output is forced off. As seen above, the remote-ON/OFF feature can also be used as a standby or power switch to turn off the TOP264-271 and keep it in a very low power consumption state for indefinitely long periods. If the TOP264-271 is held in remote-off state for long enough time to allow the CONTROL pin to discharge to the internal supply undervoltage threshold of 4.8 V (approximately 32 ms for a 47 mF CONTROL pin capacitance), the CONTROL pin goes into the hysteretic mode of regulation. In this mode, the CONTROL pin goes through alternate charge and discharge cycles between 4.8 V and 5.8 V (see CONTROL pin operation section above) and runs entirely off the high-voltage DC input, but with very low power consumption (<100 mW typical at 230 VAC with X pin open). When the TOP264-271 is remotely Voltage Monitor and External Current Limit Pin Table* Figure Number 13 14 15 16 17 18 19 20 21 22 23 24 Three Terminal Operation 3 Line Undervoltage (UV) 3 3 3 3 3 Line Overvoltage (OV) 3 3 3 3 3 Line Feed-Forward (DC MAX) 3 3 3 3 Output Overvoltage Protection (OVP) 3 Overload Power Limiting (OPP) 3 External Current Limit 3 3 3 3 3 3 Remote-ON/OFF 3 3 3 Device Reset 3 3 3 Fast AC Reset 3 AC Brown-Out 3 *This table is only a partial list of many VOLTAGE MONITOR and EXTERNAL CURRENT LIMIT Pin Configurations that are possible. Table 2. VOLTAGE MONITOR (V) Pin and EXTERNAL CURRENT LIMIT (X) Pin Configuration Options. |
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