MB3885 Fujitsu Microelectronics, Inc., MB3885 Datasheet - Page 17

• Manufacturer Part Number: MB3885
• Description: 1-channel Dc/dc Converter Ic With Synchronous Rectifier
• Manufacturer: Fujitsu Microelectronics, Inc.

SOFT-START TIME SETTING
The soft-start function prevents rush current events when the IC power is turned on, by connecting soft-start
capacitors (Cs) to the CS terminal (pin 6) .
When the IC is activated (Vcc
externally connected soft-start capacitors (Cs) at 10 A.
Because the error Amp. output (FB) is determined by the ratio of the lower of the two non-inverted input terminals
(1.25 V, CS terminal voltage) to the inverted input terminal voltage ( INE) , the soft-start interval (when CS
terminal voltage
Thus the DC/DC converter output voltage is in proportion to the rise in the CS terminal voltage as the soft-start
capacitor connected to the CS terminal charges. The soft-start time is determined by the following formula.
Soft-start time (time to output 100 )
ts (s) : = 0.125
1.25 V
2.3 V
0 V
Cs ( F)
1.25 V) FB is determined by the ratio of the INE terminal voltage and CS terminal voltage.
Soft start time ts
UVLO threshold voltage) , Q2 is off and the CS terminals begin charging the
CS terminal voltage
Error. amp block comparison voltage
to
INE voltage
MB3885
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