R1224N Datasheet, PDF (12/42 Pages) RICOH electronics devices division – PWM/VFM step-down DC/DC Converter

R1224N
External Components
1. Inductor
Select an inductor that peak current does not exceed ILmax. If larger current than allowable current flows,
magnetic saturation occurs and make transform efficiency worse.
When the load current is definite, the smaller value of L, the larger the ripple current.
Provided that the allowable current is large in that case and DC current is small, therefore, for large output
current, efficiency is better than using an inductor with a large value of L and vice versa.
2. Diode
Use a diode with low VF (Schottky type is recommended.) and high switching speed.
Reverse voltage rating should be more than VIN and current rating should be equal or more than ILmax.
3. Capacitors
As for CIN, use a capacitor with low ESR (Equivalent Series Resistance) and a capacity of at least 10µF for
stable operation.
COUT can reduce ripple of Output Voltage, therefore 47µF or more value of tantalum type capacitor is
recommended.
4. Lx Transistor
Pch Power MOSFET is required for this IC.
Its breakdown voltage between gate and source should be a few V higher than Input Voltage.
In the case of Input Voltage is low, to turn on MOSFET completely, to use a MOSFET with low threshold
voltage is effective.
If a large load current is necessary for your application and important, choose a MOSFET with low ON
resistance for good efficiency.
If a small load current is mainly necessary for your application, choose a MOSFET with low gate capacity for
good efficiency.
Maximum continuous drain current of MOSFET should be larger than peak current, ILmax.
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