MB3888 Fuji Electric, MB3888 Datasheet - Page 17

• Manufacturer Part Number: MB3888
• Description: DC/DC Converter IC for Charging Li-ion Battery
• Manufacturer: Fuji Electric

(1) Setting constant voltage mode soft-start
METHOD OF SETTING THE SOFT
For preventing rush current upon activation of IC, the IC allows soft-start using the capacitor (C
the CS terminal (pin 20) .
When CTL terminal (pin 3) is placed under “H” level and IC is activated (V
turned off and the external soft-start capacitor (C
Error Amp output (FB2 terminal (pin 6) ) is determined by comparison between the lower voltage of the two
non-inverted input terminals ( INE2 terminal (pin 8) and CS terminal voltage) and inverted input terminal voltage
( INE2 terminal (pin 7) voltage) . Within the soft-start period (CS terminal voltage
by comparison between INE2 terminal voltage and CS terminal voltage, and DC/DC converter output voltage
goes up proportionately with the increase of CS terminal voltage caused by charging on the soft-start capacitor.
Soft-start time is obtained from the following formula :
Soft-start time : ts (time to output 100
t
S
(s) : = 0.42
( INE2)
4.9 V
4.2 V
0 V
Soft-start time : ts
C
S
C
S
( F) , at INE2
4.2 V
INE2
INE2
FB2
CS
20
6
7
8
VREF
4.2 V
10 A
)
-
START TIME
Soft-start circuit
Q2
S
) connected to the CS terminal is charged at 10 A.
CS terminal voltage
Comparison with Error Amp block INE2
voltage.
10 A
Amp2
Error
CC
UVLO threshold voltage) , Q2 is
UVLO
INE2) , FB2 is determined
MB3888
S
) connected to
17