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NCP1423DMR2G Datasheet(PDF) 11 Page - ON Semiconductor |
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NCP1423DMR2G Datasheet(HTML) 11 Page - ON Semiconductor |
11 / 14 page NCP1423, SCV1423 http://onsemi.com 11 IC is enabled again, and the internal circuit typically consumes 9 mA of current from the OUT pin during normal operation. Low−Battery Detection A comparator with 15 mV hysteresis is applied to perform the low−battery detection function. When Pin 9 (LBI) is at a voltage (defined by a resistor divider from the battery voltage) lower than the internal reference voltage of 0.5 V, the comparator output turns on a 50 W low side switch. It pulls down the voltage at Pin 10 (LBO) which requires a hundred to a thousand k W of external pull−high resistance. If the Pin 9 voltage is higher than 0.5 V+15 mV, the comparator output turns off the 50 W low side switch. When this occurs, Pin 10 becomes high impedance and its voltage is pulled high again. Auto Discharge Auto discharge function is using for ensure the output voltage status after the power down occur. This function is using for communication with a digital signal. When auto discharge function is enabled, the ADEN is set high; the output capacitor will be discharged after the device is shutdown. The capacitors connected to the output are discharged by an integrated switch of 100 W. The residual voltage on VOUT will be less than 0.4 V after auto discharge. APPLICATIONS INFORMATION Output Voltage Setting A typical application circuit is shown in Figure 1, The output voltage of the converter is determined by the external feedback network comprised of R1 and R2 and the relationship is given by: VOUT + 0.5 V 1 ) R1 R2 where R1 and R2 are the upper and lower feedback resistors, respectively. Low Battery Detect Level Setting The Low Battery Detect Voltage of the converter is determined by the external divider network comprised of R3 and R4 and the relationship is given by: VLBI + 0.5 V 1 ) R3 R4 where R3 and R4 are the upper and lower divider resistors respectively. Inductor Selection The NCP1423 is tested to produce optimum performance with a 5.6 mH inductor at VIN = 1.3 V, VOUT = 3.3 V, supplying an output current up to 200 mA. For other input / output requirements, inductance in the range 3 mH to 10 mH can be used according to end application specifications. Selecting an inductor is a compromise between output current capability, inductor saturation limit and tolerable output voltage ripple. Low inductance values can supply higher output current but also increase the ripple at output and decrease efficiency. On the other hand, high inductance values can improve output ripple and efficiency; however, it also limited the output current capability at the same time. Another parameter of the inductor is its DC resistance. This resistance can introduce unwanted power loss and reduce overall efficiency. The basic rule is to select an inductor with lowest DC resistance within the board space limitation of the end application. Capacitors Selection In all switching mode boost converter applications, both the input and output terminals see impulsive voltage / current waveforms. The currents flowing into and out of the capacitors multiply with the Equivalent Series Resistance (ESR) of the capacitor to produce ripple voltage at the terminals. During the Syn−Rect switch−off cycle, the charges stored in the output capacitor are used to sustain the output load current. Load current at this period and the ESR combined and reflect as ripple at the output terminals. For all cases, the lower the capacitor ESR, the lower the ripple voltage at output. As a general guideline, low ESR capacitors should be used. PCB Layout Recommendations Good PCB layout plays an important role in switching mode power conversion. Careful PCB layout can help to minimize ground bounce, EMI noise, and unwanted feedback that can affect the performance of the converter. Hints suggested below can be used as a guideline in most situations. Grounding A star−ground connection should be used to connect the output power return ground, the input power return ground, and the device power ground together at one point. All high−current paths must be as short as possible and thick enough to allow current to flow through and produce insignificant voltage drop along the path. The feedback signal path must be separated from the main current path and sense directly at the anode of the output capacitor. Components Placement Power components (i.e. input capacitor, inductor and output capacitor) must be placed as close together as possible. All connecting traces must be short, direct and thick. High current flowing and switching paths must be kept away from the feedback (FB, Pin 3) terminal to avoid unwanted injection of noise into the feedback path. |
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Similar Description - NCP1423DMR2G |
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