MB3883 Datasheet, PDF (22/39 Pages) Fujitsu Component Limited. – 6-ch DC/DC Converter IC With Synchronous Rectification for voltage step-up and step-down

MB3883
2. Soft Start Settings
• CH6 soft start time
The soft start operation is determined by the capacitor (C+IN6) connected to the C+IN6 terminal (pin 5). The
soft start time depends on the input voltage and load current.
CH6 soft start time
( ) ^{ts (s) = − C+IN6 (F) × 37.5 (kΩ) × 62.5 (kΩ) ln 1 − VC+IN6 (V)}
100 (kΩ)
1.26 (V)
VC+IN6
C+IN6
5
C+IN6
(1.26 V)
(VB : 2 V)
−
(37.5 kΩ)
+
(62.5 kΩ)
Error
Amp.6
CH6 soft start equivalent circuit
Example: The soft start time until CH6 output voltage reaches 95% of the set voltage is determined as follows:
ts (s) =: 0.07 × C+IN6 (µF)
• CH1 to CH5 soft start time
CH1 to CH5 soft start time
ts (s) =: 1.25 × CS (µF)
Note : The short-circuit detection function remains working during soft start operation on channels 1 through 5.
s SETTING THE TRIANGULAR OSCILLATOR FREQUENCY
The triangular oscillator frequency is determined by the timing capacitor (CT) connected to the CT terminal (pin
26), and the timing resistor (RT) connected to the RT terminal (pin 25).
Triangular oscillator frequency
fOSC (kHz) =:
900000
CT (pF) •RT (kΩ)
22