DC/DC Converter Application Note
Internal or External Output Transistors
Ricoh’s DC/DC converters are equipped with internal or external output transistors. The device equipped with an internal output transistor and the LX pin is classified as DC/DC converter. The device equipped with an external output transistor and the EXT pin is classified as DC/DC controller. The device equipped with both internal and external output transistors is listed along with the DC/DC converters.
A power MOSFET should be used with the external output transistor type. To achieve high efficiency under heavy load, a MOSFET with a low ON resistance should be used. To achieve high efficiency under light load, a MOSFET with a small gate capacity should be used. As for MOSFETs, the maximum drain current should be higher than the maximum inductor current.