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HM1480 데이터시트(HTML) 7 Page - Shenzhen Huazhimei Semiconductor Co., Ltd

부품명 HM1480
상세내용  Input range synchronous buck controller
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제조사  HMSEMI [Shenzhen Huazhimei Semiconductor Co., Ltd]
홈페이지  http://www.hmsemi.com/
Logo HMSEMI - Shenzhen Huazhimei Semiconductor Co., Ltd

HM1480 데이터시트(HTML) 7 Page - Shenzhen Huazhimei Semiconductor Co., Ltd

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7
Setting Output Voltage
The output voltage is set with a resistor divider from the output node to the FB pin. It is recommended 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 10k? to 1M?
range is suggested for R4. R3 is then given by:
R3 = R4 ? [(VOUT / VREF) ? 1]
where VREF is 1.21V.
Inductor Selection
For most applications, the value of the inductor will fall in the range of 4.7?H to 47?H. Its value is chosen
based on the desired ripple current. Large value inductors lower ripple current and small value inductors
result in higher ripple currents. Higher VIN or VOUT also increases the ripple current as shown in equation.
A reasonable starting point for setting ripple current is ?IL = 800mA (40% of 2A).
The DC current rating of the inductor should be at least equal to the maximum load current plus half the
ripple current to prevent core saturation. Thus, a 2.8A rated inductor should be enough for most
applications (2A + 800mA). For better efficiency, choose a low DC-resistance inductor.
Different core materials and shapes will change the size/current and price/current relationship of an
inductor. Toroid or shielded pot cores in ferrite or perm alloy materials are small and don?t radiate much
energy, but generally cost more than powdered iron core inductors with similar electrical characteristics.
The choice of which style inductor to use often depends more on the price vs. size requirements and
any radiated field/EMI requirements than on what the
HM1480 requires to operate.
Output and Input Capacitor Selection
In continuous mode, the source current of the top MOSFET is a square wave of duty cycle VOUT/VIN. To
prevent large voltage transients, a low ESR input capacitor sized for the maximum RMS current must be
used. The maximum RMS capacitor current is given by:
This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst-case condition is
commonly used for design because even significant deviations do not offer much relief. Note that the
capacitor manufacturer?s ripple current ratings are often based on 2000 hours of life. This makes it
advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than
required. Always consult the manufacturer if there is any question.


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