Technical Note

8/13

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2010.09 - Rev.A

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BD8646FV

VENH

0V

0V

0V

(=50µsec)

①

②

③

EN terminal

SS terminal

Output setting voltage

●

External parts setting method

1 Output voltage setting method

The output voltage can be arbitrarily set by external resistance.

VREF

R2

R2)

(R1

Vo





Please select the constant of R1 and R2 by this expression.

Please select the current that flows to R1 and R2 to become much smaller than output current.

FB

R1

R2

Vo

VREF=0.8V

Fig.16 Output voltage setting circuit

2 Soft start time setting method

BD8646FV can soft start without overshoot because of a charge current to the soft start capacitance (CSS).

The soft start time can be set by connecting soft start capacity (CSS).

When the EN terminal voltage is set VIN_EN or more, the charge to the capacity between SS/DELAY and GND terminal is

begun. The output voltage becomes soft start in proportion to a SS/DELAY terminal voltage rising. When the SS/DELAY

terminal voltage exceeds VSSTH, the output voltage is fixed in a setting value.

Please set soft start time (tss) in 1msec-52.5msec.

Fig.17 Soft start

Min.

Typ.

Max.

35µsec

50µsec

75µsec

①

②

③

)

A

μ

4

(

I

C

)

V

(V

)

A

μ

4

(

I

C

)

V

6

.

0

(

V

)

s

μ

50

(

TW

T

SS

SS

OST

SSTH

SS

SS

OST

EN

VO



















