MB39A114 Datasheet, PDF (21/54 Pages) Fuji Electric – DC/DC Converter IC for Charging Li-ion Battery

MB39A114
(2) Setting constant current 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 activated (VREF ≥ UVLO threshold voltage), Q2 becomes off
and the external soft-start capacitors (CS) connected to CS terminal are charged at 10 µA.
The error amplifier1 output (FB12 terminal (pin 7) ) is determined by comparison between the lower voltage of
the two non-inverted input terminal voltage (+INE1 terminal (pin 9) voltage, CS terminal voltages) and the inverted
input terminal voltage (−INE1 terminal (pin 8) voltage). The FB12 is decided for the soft-start period (CS terminal
voltage < +INE1) by the comparison between −INE1 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 error amplifier2 output (FB12 terminal (pin 7) ) is determined by comparison between the lower voltage of
the two non-inverted input terminal voltage (+INE2 terminal (pin 3) voltage, CS terminal voltages) and the inverted
input terminal voltage (−INE2 terminal (pin 4) voltage). The FB12 is decided for the soft-start period (CS terminal
voltage < +INE2) by the comparison between −INE2 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) =: +INE1 (+INE2) /10 µA × CS (µF)
=: 4.9 V
+INE1
(+INE2)
=: 0 V
Soft-start time : ts
CS terminal voltage
Comparison voltage with Error Amp1block
−INE1 voltage
(comparison voltage with Error Amp2 block
−INE2 voltage)
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