BD8649EFV Datasheet, PDF (8/14 Pages) Rohm – Flexible Step-down Switching Regulator with Built-in Power MOSFET

BD8649EFV
●External parts setting method
1 Output voltage setting method
The output voltage can be arbitrarily set by external resistance.
Vo

(R1 R2)
R2
VREF
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.
Vo
R1
FB
R2
Technical Note
VREF=0.8V
Fig.16 Output voltage setting circuit
2 Soft start time setting method
BD8649EFV 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.
TVO

TW EN( 
50μs) 
VOST( 0.6V)  CSS
ISS( 4μA)

(VSSTH  VOST)  CSS
ISS( 4μA)
①
②
③
EN terminal
SS terminal
VENH
0V
①
TWEN
(=50µsec)
VSSTH(=1.4V[typ])
0V
VOST(=0.6V[typ])
②
TW_ENSPEC
Min.
Typ.
Max.
35µsec 50µsec 75µsec
Output setting voltage _0V
③
TVO
Fig.17 Soft start
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8/13
2010.09 - Rev.A