MB3759 Datasheet, PDF (15/27 Pages) Fujitsu Component Limited. – Switching Regulator Controller (Switchable between push-pull and single-end functions)

3. Soft Start
A soft start function can be incorporated by using the dead-time control element.
MB3759
VREF
R1
VD =
R2
R1+R2
VR
Cd
DT
R2
Rd
VREF
DT
Setting the dead-time
Incorporating soft start
When the power is turned on, Cd is not yet charged and the DT input is pulled to the VREF pin causing the output
transistor to turn off. Next, the input voltage to the DT pin drops in accordance with the Cd, Rd constant causing
the output pulse width to increase steadily, providing stable control circuit operation.
If you wish to use both dead-time and softstart, combine these in an OR configuration.
Cd
R1
Rd
R2
VREF
DT
4. Output Current Limiting (Fallback system using a detection resistor inserted on the output side)
(1) Typical example
VREF
R3
VIO
+
−
R4
RS ^IO
VO
R1
D _R5
R2
GND
VO
VO1
0
IO
0
IL3 IL2
IL1
15