MB3800 Datasheet, PDF (13/21 Pages) Fujitsu Component Limited. – Switching Regulator Controller (Low Voltage)

MB3800
10.3 Other Functions
10.3.1 Soft start and short circuit detection
Soft start operation is set by connecting capacitor C_PE 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 V_OM+ and capacitor C_PE 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”.)
10.3.2 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.
11. 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. Notes On Use
■ Take account of common impedance when designing the earth line on a printed wiring board.
■ Take measures against static electricity.
❐ For semiconductors, use antistatic or conductive containers.
❐ When storing or carrying a printed circuit board after chip mounting, put it in a conductive bag or container.
❐ The work table, tools and measuring instruments must be grounded.
❐ The worker must put on a grounding device containing 250 kΩ to 1 MΩ resistors in series.
■ Do not apply a negative voltage
❐ Applying a negative voltage of 0.3 V or less to an LSI may generate a parasitic transistor, resulting in
malfunction.
Document Number: 002-08716 Rev. *A
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