MB3888 Datasheet, PDF (15/30 Pages) Fujitsu Component Limited. – DC/DC Converter IC for Charging Li-ion Battery

MB3888
The PWM comparator circuit compares the triangular wave generated by the triangular wave oscillator to the
error amplifier output voltage or DTC terminal voltage, and turns on the external output transistor during the
interval in which the triangular wave voltage is lower than the error amplifier output voltage.
(7) Output block (OUT)
The output circuit uses a totem-pole configuration capable of driving an external P-channel MOS FET.
The output “L” level sets the output amplitude to 6 V (Typ) using the voltage generated by the bias voltage block
(VH) .
This results in increasing conversion efficiency and suppressing the withstand voltage of the connected external
transistor in a wide range of input voltages.
(8) Control block (CTL)
Setting the CTL terminal (pin 3) at “L” level places the IC in the standby mode. (The supply current is 10 µA at
maximum in the standby mode.) Setting the CTL terminal at “H” level generates an internal reference voltage,
placing the system under outputting status.
CTL function table
CTL
Power
OUTD
L
OFF (Standby)
Hi-Z
H
ON (Active)
L
(9) Bias voltage block (VH)
The bias voltage circuit outputs VCC −6 V (Typ) as the minimum potential of the output circuit. In the standby
mode, this circuit outputs the potential equal to VCC.
2. Protection Functions
Under voltage lockout protection circuit (UVLO)
The transient state or a momentary decrease in supply voltage or internal reference voltage (VREF) , which
occurs when the power supply (VCC) is turned on, may cause malfunctions in the control IC, resulting in
breakdown or degradation of the system.
To prevent such malfunction, the under voltage lockout protection circuit detects a supply voltage or internal
reference voltage drop and fixes the OUT terminal (pin 18) to the “H” level. The system restores voltage supply
when the supply voltage or internal reference voltage reaches the threshold voltage of the under voltage lockout
protection circuit.
Protection function (UVLO) operation table
When UVLO is operating (VCC or VREF voltage is lower than UVLO threshold voltage) .
OUTD
OUT
CS
Hi-Z
H
L
3. Soft-Start Function
Soft-start block (SOFT)
Connecting a capacitor to the CS terminal (pin 20) prevents surge currents when the IC is turned on. Using an
error amplifier for soft-start detection makes the soft-start time constant, being independent of the output load
of the DC/DC converter.
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