R1221N Datasheet, PDF (10/21 Pages) RICOH electronics devices division – Step-down DC/DC Converter with Voltage Detector

3. Capacitor
As for CIN, use a capacitor with low ESR(Equivalent Series Resistance) and a capacity of at least 10mF for stable
operation.
COUT can reduce ripple of Output Voltage, therefore 47mF to 100mF tantalum type is recommended.
4. Lx Transistor
Pch Power MOS FET is required for this IC.
Its breakdown voltage between gate and source should be a few volt higher than Input Voltage.
In the case of Input Voltage is low, to turn on MOS FET completely, select a MOS FET with low threshold voltage.
If a large load current is necessary for your application and important, choose a MOS FET with low ON resistance
for good efficiency.
If a small load current is mainly necessary for your application, choose a MOS FET with low gate capacity for good
efficiency.
Maximum continuous drain current of MOS FET should be larger than peak current, ILmax.
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Rev. 1.11
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