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HM1483B データシート(PDF) 6 Page - Shenzhen Huazhimei Semiconductor Co., Ltd |
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HM1483B データシート(HTML) 6 Page - Shenzhen Huazhimei Semiconductor Co., Ltd |
6 / 9 page - 6- Application Information The operates by a constant frequency, current mode architecture. The output voltage is set by an external divider returned to the FB pin. An error amplifier compares the divided output voltage with a reference voltage of 1.21V and ad- justs the peak inductor current accordingly. During normal operation, the internal P-channel MOSFET is turned on each cycle when the oscilla- tor sets the RS latch, and turned off when the cur- rent comparator, resets the RS latch. While the P- channel MOSFET is off, the N-channel MOSFET is turned on until either the inductor current starts to reverse, as indicated by the current reversal com- parator or the beginning of the next clock cycle. Thermal Protection The total power dissipation in is limited by a thermal protection circuit. When the device temperature rises to approximately 145℃, this cir- cuit turns off the output, allowing the IC to cool. The thermal protection circuit can protect the de- vice from being damaged by overheating in the event of fault conditions. Continuously running the into thermal shutdown degrades device reliability. Current Limit Current limit detection occurs during the off-time by monitoring the current through the low-side switch using an external resistor, RLIM. The current limit value is defined by RLIM. If during the off-time the current in the low-side switch exceeds the user defined current limit value, the next on-time cycle is immediately terminated. Current sensing is achieved by comparing the voltage across the low side FET with the voltage across the current limit set resistor RLIM. For example, the current limit value is 2.1A by the RLIM =50k. The current limit value rises when the set resistor RLIM rises. The maximum output current is set by RLIM: RLIM (kΩ) = 23• IMAX (A). Oscillator Frequency The oscillator frequency is set by a sin- gle external resistor connected between the RT pin and the GND pin. The resistor should be located very close to the device and connected directly to the pins of the IC (RT and GND). An internal ampli- fier holds the RT pin at a fixed voltage typically 0.6V. The oscillator frequency rises when the re- sistor RT falls. To determine the timing resistance for a given switching frequency, use the equation below: RT(kΩ)= [6500/fOSC(kHz)] 2 Setting Output Voltage The output voltage is set with a resistor divider from the output node to the FB pin. It is recom- mended to use divider resistors with 1% tolerance or better. To improve efficiency at very light loads consider using larger value resistors. If the values are too high the regulator is more susceptible to noise and voltage errors from the FB input current are noticeable. For most applications, a resistor in the 10kΩ to 1MΩ range is suggested for R3. R2 is then given by: R2 = R3 • [(VOUT / VREF) – 1] where VREF is 1.21V. Output Cable Resistance Compensation To compensate for resistive voltage drop across the charger's output cable, the inte- grates a simple, user-programmable cable voltage drop compensation using the impedance at the FB pin. Choose the proper feedback resistance values for cable compensation refer to the curve in Figure 1. The delta VOUT voltage rises when the feed- back resistance R3 value rises. The delta VOUT voltage rises when the feedback resistance R3 value rises, use the equation below: ΔVOUT(V) = R3(kΩ) • IOUT(A)/1100 Figure 1. Delta Output Voltage vs. Load Current |
同様の部品番号 - HM1483B |
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同様の説明 - HM1483B |
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