MB39C308 Datasheet, PDF (54/60 Pages) Fujitsu Component Limited. – 6ch DC/DC Converter IC for LPIA Platform VR

MB39C308
7. Partial short circuits
Normally, in the event of a short circuit, such as the DC/DC output connecting to ground or low potential point,
output is stopped by the short circuit protection (SCP) function. Take care in the event of a partial short circuit,
because the output is not stopped by the short circuit protection (SCP) function. It is recommended that a fuse
be inserted into the input. If the short circuit conditions partially occur in several channels which contain the FET,
there is a possibility of smoke or fire.
[Partial short circuit : Refers to a short circuit condition where overcurrent flows but is not strong enough to
decrease the output voltage.]
8. Affects of insufficient power supply capacity on the SCP latch function
If the large current exceeding the current limit of input power supply flows through this device such as the case
of output short, power supply voltage may drop. On such occasion, if the power supply voltage drops below 5
V (Typ) before it detects SCP, DC/DC output is shutdown by the UVLO (Under Voltage Lock Out) function. After
the DC/DC output is shutdown, the input power supply recovers and SCP timer is reset, then the DC/DC converter
starts operating again. As the results, the DC/DC output does not stop at SCP latch function, and the following
four processes are repeated in the following order. In addition, it should be noted that under the above conditions,
some components of the DC/DC converter may be destroyed.
1. Power supply voltage drops as power supply current reaches its limit.
2. DC/DC output is shutdown by UVLO.
3. UVLO is released.
4. Output current and power supply current increase.
It is recommended that a fuse be inserted into the power line. If output wires are short-circuited in the multiple
channels which contain the FET, there is a possibility of smoke or fire.
Normal SCP operation
output short
Power supply voltage
DC/DC output voltage
UVLO
threshold
No SCP latch
output short
UVLO
DC/DC output current
Power supply current
time
counting
power supply
current limit
SCP latch
1 2 4 1...
3
hysteresis
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DS04-27261-6E