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VIPER25HD Datasheet(PDF) 33 Page - STMicroelectronics |
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VIPER25HD Datasheet(HTML) 33 Page - STMicroelectronics |
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33 / 40 page 
VIPER25 Operation description Doc ID 15585 Rev 4 33/40 Fixed the VINon and the VINoff levels, with reference to Figure 38, the following relationships can be established for the calculation of the resistors RH and RL: Equation 12 Equation 13 For a proper operation of this function, VIN on must be less than the peak voltage at minimum mains and VIN off less than the minimum voltage on the input bulk capacitor at minimum mains and maximum load. The BR pin is a high impedance input connected to high value resistors, thus it is prone to pick up noise, which might alter the OFF threshold when the converter operates or gives origin to undesired switch-off of the device during ESD tests. It is possible to bypass the pin to ground with a small film capacitor (e.g. 1-10 nF) to prevent any malfunctioning of this kind. If the brown-out function is not used the BR pin has to be connected to GND, ensuring that the voltage is lower than the minimum of VDIS threshold (50 mV, see Table 8). In order to Figure 38. Brown-out protection: BR external setting and timing diagram - + Disable C BR V DIS - + V in_OK V BRth R H I BRhyst R L V IN_DC VDD + V OUT V IN V INon V INoff V DRAIN_START V BR V in_OK I BR V BRth I BRhyst V DD V DDon V DDoff V DS V DD(RESTART) BRhyst BRth BRth INoff BRhyst INoff INon BRhyst BRhyst L I V V V V V V I V R × − − − + − = BRhyst BRhyst L L BRhyst BRhyst INoff INon H I V R R I V V V R + × − − = |
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