MB39A123 Datasheet, PDF (32/44 Pages) Fujitsu Component Limited. – 6 ch DC/DC Converter IC with Synchronous Rectification

MB39A123
• Operation waveform when CTL turning on and off
CTL
VR
VREF
UVLO1
UVLO2
ch.1 to ch.4
Output Drive
circuit control
ch.5, ch.6
Output Drive
circuit control
H ^∗2
L
1.23 V
0V
2V
0V
H
UVLO state
L
H
UVLO state
L
H
Fixed full off
L
H
Fixed full off
L
VTH1
VTH2
UVLO release
UVLO release
Possible operate
Possible operate
∗1
VRST1
VRST2
UVLO state
UVLO state
Fixed full off
Fixed full off
*1 : As shown in the sequence on the above figure, when turning off CTL while each CHCTL is turned on, intermission
state may be generated due to noise around the CTL threshold voltage. To prevent this, it is recommended
to turn off CTL with a slope of - 1 V/50 µs or higher so that the CTL voltage does not remain in the specified
threshold voltage range (0.5 V to 1.5 V) . If the above slope setting is difficult to achieve, it is recommended
to turn off CTL after turning off all CHCTLs.
Moreover, a voltage remains in the FB terminal, when VCC is turned off at the same time as CTL and CHCTL,
or when VCC is turned off at the same time as CTL while each CHCTL is still turned on. As this may lead to
an overshoot upon restart, it is recommended to turn off VIN and CTL after turning off all the CHCTLs to reduce
FB to 0V.
Likewise, it is recommended to turn off CHCTL with a slope of - 1 V/50 µs or higher.
*2 : When CTL and CHCTL are turned on at the same time, or when CTL is turned on while each CHCTL is turned
on, there exists a period (approx. 200 ns) when the error Amp output voltage (FB) is higher than the triangular
wave voltage (CT) upon the startup of VREF. As a result, when UVLO is released and then the Output Drive
circuit of each channel becomes operable, the output transistor is turned on, generating a voltage at the DC/
DC converter output.
The voltage to be generated (Vop) depends on L, Co and VIN. (See • Vo characteristics (Vop) when turning on CTL
at CHCTL ON.)
It should be noted that the above event does not occur when CTL is turned on while CHCTL is turned off.
Therefore, it is recommended to turn on each CHCTL after turning on CTL.
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