MB39A108 Datasheet, PDF (4/4 Pages) Fujitsu Component Limited. – 5-Channel DC/DC Converter IC with Synchronous Rectification

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MB39A108
capable of driving an external Pch MOS FET (channel 1 main
side, channels 2 and 3) and Nch MOS FET (channel 1
synchronous rectification side, channels 4 and 5).
s Channel Control Function
The ON/OFF status for each channel is set via the voltage
setup at the CTL terminals or the CTL1 to CTL5 terminals.
Table 1 shows the ON/OFF setup conditions for each
channel.
s Protection Circuit Functions
Timer Latch Short-circuit Protection Circuit Block (SCP)
The short-circuit detection comparator (SCP Comp.)
constantly compares the output level of the error amplifier and
the reference voltage in each channel.
When the DC/DC converter load condition is stable in all
channels, the CSCP terminal and output from the short-circuit
detection comparator both stay at th_Ê e L_Ê¡level. When the
load condition changes rapidly due to a load short-circuit, etc.
and the output voltage drops, the output from the short-
circuit detection comparator climbs to th_Ê e H_Ê¡level. At this
point, charging commences in the short-circuit protection
capacitor Cscp externally attached to the CSCP terminal.
When the capacitor Cscp charge reaches the threshold voltage
(VTH˺0.70V), it sets the latch and turns OFF the external FET
(sets the dead time to 100ˋ). The latch input then closes and
the CSCP terminal is maintained at the_Ê L_Ê¡level. The latch
on the timer latch short-circuit protection circuit can be
canceled by cutting off the power supply (VCC) or turning
the CTL terminal to the_Ê L_Ê¡level.
Undervoltage Lockout Circuit Block (UVLO)
The transient state at normal power start-up and momentary
drops in the power supply voltage may lead to malfunctions in
a control IC, and in worse cases system deterioration or
destruction. To prevent these types of malfunction, the
undervoltage lockout circuit block detects the internal reference
voltage level by monitoring the power supply voltage, turns
OFF the output FET, and sets the dead time to 100% while
simultaneously maintaining the CSCP terminal at the_Ê L_Ê¡level.
The system restores itself once the power supply voltage exceeds
the threshold voltage of the undervoltage lockout circuit.
s Soft-start Function
Soft-start Block (CS)
Possible inrush current at power start-up can be prevented by
connection of a capacitor to the CS terminal of each channel.
Performing soft-start detection in the error amplifier enables
soft-start operation at a fixed timing independent from the
DC/DC converter output load.
✱
Figure 2 Pin Assignments
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52 FIND Vol.21 No.3 2003