BD9421F_15 Datasheet, PDF (18/31 Pages) Rohm – White LED Driver for large LCD Panels (DCDC Converter Type)

BD9421F
Datasheet
○Selection of switching MOSFET transistors
There will be no problem for switching MOSFET transistors having absolute maximum rating higher than rated current
of the inductor L and VF higher than “C_OUT breakdown voltage  Rectifier diode”. However, to achieve high-speed
switching, select transistors with small gate capacity (injected charge amount).
Note: Rated current larger than overcurrent protection setting current is recommended.
Note: Selecting transistors with low on resistance can obtain high efficiency.
○Selection of rectifier diodes
Select Schottky barrier diodes having current capability higher than the rated current of the inductor L and inverse
breakdown voltage higher that C_OUT breakdown voltage, particularly having low forward voltage VF.
○Selection of Load switch MOSFET and soft start function
In usual DC/DC converter, because there is no switching to a path leading from V_IN to V_OUT resulting in output voltage
is also occurring even if IC is in OFF state. Please insert PMOSFET between V_IN and inductor if you want voltage to 0V
until the IC starts to operate. In addition, FAIL pin can be used for driving load switch after confirmed the logic theory,
and the breakdown voltage of drain-source needed to be selected larger than V_IN.
Furthermore, if you would like to make soft start function to load switch, please insert a condenser between Gate
and Source.
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TSZ22111 • 15 • 001
18/27
TSZ02201-0F1F0C100310-1-2
25.Sep.2015 Rev.003