FREQ datasheet(29/56 Pages) FUJITSU

29 / 56 page

MB39A214A

Limitation : development tool vendor use only

FUJITSU SEMICONDUCTOR CONFIDENTIAL

DS405-00007-1v0-E

Setting switching frequency

The switching frequency is set at the FREQ pin. As for the setting process, see the switching frequency

control function table.

Setting over current limitation

The over current limitation value can be set by adjusting the over current limitation setting resistor value

connected to the ILIM pin.

Calculate the resistor value by the following formula.

ΔIL

RLIM = 10

RON_Sync

(ILIM −

)

RLIM

: Over current limitation value setting resistor [Ω]

ILIM

: Over current limitation value [A]

ΔIL

: Ripple current peak-to-peak value of inductor [A]

RON_Sync

: ON resistance of low-side FET [Ω]

ILIM

RLIM

IOUT

ILIM

If the rate of inductor saturation current is small, the inductor value decreases and the ripple current of

inductor increase when the over-current flows. At that time there is a possibility that the limited output

current increases or is not limited, because the bottom of inductor current is detected. It is necessary to use

the inductor that has enough large rate of inductor saturation current to prevent the overlap current.

Inductor current

Over current

limitation value

Time

ΔIL

FREQ Datasheet(PDF) 29 Page - fujitsu semiconductor