MB3832A
s METHODS OF SETTING THE SOFT START TIME
To prevent surge currents when the IC is turned on, you can set a soft start using the DTC terminal (pin 16).
When power is switched on, the current begins charging the capacitor (Cdt) connected the DTC terminal. The
soft start process operates by comparing the soft start setting voltage, which is proportional to the DTC terminal
voltage, with the triangular waveform, and varying the ON-duty of the OUT terminal (pin 19).
The soft start time until the ON duty reaches 50 % is determined by the following equation:
For figure c
Soft start time (time until output ON duty = 50%)
ts (s) = Cdt (F) × Rdt (Ω) × ln(1 − 1.6/2.5) =: 1.022 × Cdt (F) × Rdt (Ω)
For figure d
Soft start time (time until output ON duty = 50%)
ts (s) = −
Cdt (F) × R1 (Ω) × R2 (Ω)
R1 (Ω) + R2 (Ω)
× ln (1 −
1.6 (R1 (Ω) + R2 (Ω)) )
2.5R2 (Ω)
• Figure c Setting a soft start
1 VREF
Rdt
16 DTC
Cdt
• Figure d Setting the dead time and a soft start
1 VREF
R1
16 DTC
Cdt
R2
18