Technical Note

9/13

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2010.09 - Rev.A

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BD8646FV

△

3 Selection of inductor (L)

Please select the value of the inductor according to the following expressions.

f

V

I

V

)

V

(V

L

IN

L

OUT

OUT

IN











⊿

[H]

(⊿ IL: Output ripple current , f: Switching frequency)

※

Please have and select an enough margin so that the

current peak should not exceed the ratings current value

of the inductor.

Fig.18 Current of output ripple

4 Selection of input capacitor (Cin)

Please use a low ESR input capacitor which can be used with high voltage and ripple current to prevent a big transition

voltage.

※

Please put on the input capacitor near side by VIN-PGND.

5 Selection of diode

Please have and set the margin enough to the current rating of the diode for the maximum load current.

Moreover, please similarly have and set the margin enough to a ratings reverse-voltage for the maximum input voltage.

C1

R1

FB

FC

Fig.19 Phase amends part external circuit chart

6 OFFLATCH time setting method

If it continues abnormal state, BD8646FV output become low voltage and state is fixed.

In this case, the OFFLATCH time can be set by connecting capacitor between PSET and GND. Please select the value of

OFFLATCH time according to the following expression. Please set OFFLATCH time in 200usec～5msec.

[sec]・・・(11)

To release the off latch state, EN or VIN terminal voltage should be changed to low level once time.