MB39A114 Datasheet, PDF (20/54 Pages) Fuji Electric – DC/DC Converter IC for Charging Li-ion Battery

MB39A114
s SETTING THE SOFT START TIME
(1) Setting constant voltage mode soft start
To prevent rush currents when the IC is turned on, you can set a soft-start by connecting soft-start capacitors
(CS ) to the CS terminal (pin 22).
When CTL terminal (pin 14) is “H” levels and IC is activated (VCC ≥ UVLO threshold voltage), Q2 becomes off
and the external soft-start capacitors (CS) connected to CS terminal are charged at 10 µA.
The error amplifier output (FB3 terminal (pin 15) ) is determined by comparison between the lower voltage of
the two non-inverted input terminal voltage (internal reference voltage 4.2 V (Typ) , CS terminal voltages) and
the inverted input terminal voltage (−INE3 terminal (pin 16) voltage). The FB3 is decided for the soft-start period
(CS terminal voltage < 4.2 V) by the comparison between −INE3 terminal voltage and CS terminal voltage. The
DC/DC converter output voltage rises in proportion to the CS terminal voltage as the soft-start capacitor externally
connected to the CS terminal is charged. The soft-start time is obtained from the following formula :
Soft start time : ts (time until output voltage 100%)
ts (s) =: 0.42 × CS (µF)
=: 4.9 V
=: 4.2 V
CS terminal voltage
Internal reference voltage
in Error Amp block
=: 0 V
Soft-start time : ts
VREF
FB3 ¹⁵
−INE3 16
CS
22
CS
10 µA
10 µA
Error
Amp3
−
+
+
4.2 V
Q2
Soft start circuit
UVLO
20