MB3800_06 Datasheet, PDF (12/20 Pages) Fujitsu Component Limited. – Switching Regulator Controller (Low Voltage)

MB3800
3. Other Functions
(1) Soft start and short circuit detection
Soft start operation is set by connecting capacitor CPE to the SCP pin (pin 2). Soft start prevents a current spike on
start-up.
On completion of soft start operation, the SCP pin (pin 2) stays low and enters the short circuit detection wait state.
When an output short circuit occurs, the error amplifier output is fixed at VOM+ and capacitor CPE starts charging.
After charging to approximately 0.8 V, the OUT pin (pin 5) is set low and the SCP pin (pin 2) stays low.
Once the protection circuit operates, the circuit can be restored by resetting the power supply. (See “■ HOW TO
SET THE TIME CONSTANT FOR SOFT START AND SHORT CIRCUIT DETECTION”.)
(2) Circuit to prevent malfunction at low input voltage
Transients when powering on or instantaneous glitches in the supply voltage can lead to malfunction of the control
IC and cause system damage or failure. The circuit to prevent malfunction at low input voltage detects a low input
voltage by comparing the supply voltage to the internal reference voltage. On detection, the circuit fixes the OUT
pin (pin 5) to low.
The system recovers when the supply voltage rises back above the threshold voltage of the malfunction prevention
circuit.
■ APPLICATION EXAMPLE
18 kΩ
22 µH
ÐIN
1
FB
8
V in
+
(3 V)
33 µF
SCP ₂
V CC ₃
BR/CTL
4
0.1 µF
MB3800
7 ^OSC
6 ^GND
OUT
5
2 kΩ
390 Ω
270 pF
0.1 µF
3 kΩ
Vo
(5 V)
+
10 µF
CTL
12