MB3800 Fujitsu Microelectronics, Inc., MB3800 Datasheet - Page 12

• Manufacturer Part Number: MB3800
• Description: Switching Regulator Controller (low Voltage)
• Manufacturer: Fujitsu Microelectronics, Inc.

12
MB3800
3. Other Functions
(1) Soft start and short circuit detection
Soft start operation is set by connecting capacitor C
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 V
After charging to approximately 0.8 V, the output 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 output
pin to low.
The system recovers when the supply voltage rises back above the threshold voltage of the malfunction prevention
circuit.
APPLICATION EXAMPLE
(3 V)
V in
33 F
2 k
0.1 F
CTL
BR/CTL
SCP
390
V
–IN
CC
1
2
3
4
MB3800
PE
to the SCP pin (pin 2). Soft start prevents a current spike on
18 k
8
7
6
5
FB
OSC
GND
OUT
270 pF
OM
+ and capacitor C
3 k
22 H
0.1 F
PE
starts charging.
10 F
V o
(5 V)