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NCP5355PDR2 Datasheet(PDF) 7 Page - ON Semiconductor |
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NCP5355PDR2 Datasheet(HTML) 7 Page - ON Semiconductor |
7 / 12 page NCP5355 http://onsemi.com 7 APPLICATIONS INFORMATION Enable Pin The Enable pin allows logic level On/Off control of the NCP5355. A Logic Level Low (< 0.8 V) disables the part by forcing both TG and BG low. Bringing both gates low prevents the output voltage from ringing below ground at turn−off. A Logic Level High (> 2.0 V) enables the part by allowing CO to control TG and BG. If the Enable function is not being used, the Enable pin should be left unconnected. This will Enable the part by default, as the Enable pin will be internally pulled high by a 2.0 mA current. The maximum high voltage level is 5.0 V. Voltages greater than this may damage the part. Undervoltage Lockout Gates TG and BG are both held low until Vs reaches the UVLO Start Threshold of 8.0 V during startup. Vs exceeding the UVLO threshold allows CO to take control of both gates. If Vs falls below the UVLO Stop Threshold of 7.0 V, both gates are then forced low until Vs again exceeds the Start Threshold. Supply Capacitor Selection A 1.0 mF ceramic capacitor (CVS in Figure 4) should be located close to the Vs supply pins to provide peak current and to reduce noise. A small 1.0 W to 5.0 W resistor (RVS in Figure 4) may also be added in series with CVS to provide additional filtering in noisy environments. Bootstrap Capacitor Selection The size of the Top MOSFET bootstrap capacitor (CBST in Figure 4 ) is determined from the following equation: CBST w QTtopFETs DVBST where QTtopFETs is the sum of the Top MOSFETs total gate charge, DVBST is the maximum change in voltage across the bootstrap capacitor and is typically designed for a drop of less than a 1.0 V. For example, a circuit using one Top MOSFET with a typical QTtopFETs of 60 nC (at 12 V Vgs) and 1.0 V of droop would give a minimum value for CBST of 60 nF. Internal or External Bootstrap Diode For convenience, a bootstrap diode is internally provided by the NCP5355. This internal diode reduces system cost and parts count. However, this diode will have higher losses than a standard small signal switching or Schottky diode. By using an external Schottky diode (DBST in Figure 4) a small improvement in efficiency can be achieved as illustrated by the graph in Figure 5. While the difference in efficiency is relatively small, this difference represents heat loss in the driver and on average driver temperature may be reduced by about 10 °C if using an external diode. If an external diode is used, it should be a Schottky or switching diode. (For example: ON Semiconductor Part Number BAT54HT1 or BAS16HT1.) Adaptive Nonoverlap The NCP5355 includes adaptive nonoverlap protection to prevent top and bottom MOSFET cross conduction. When CO goes low signaling TG to turn off the top MOSFET, BG does not go high until the switch node (DRN pin) has fallen below 5.0 V and a fixed amount of delay (tpdhBG) has elapsed. This ensures that the top MOSFET is off before the bottom MOSFET is turned on. |
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Similar Description - NCP5355PDR2 |
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