LTM4620A_15 Datasheet, PDF (24/40 Pages) Linear Technology – Dual 13A or Single 26A DC/DC Module Regulator

LTM4620A
APPLICATIONS INFORMATION
The LTM4620A module has been designed to effectively
remove heat from both the top and bottom of the pack-
age. The bottom substrate material has very low thermal
resistance to the printed circuit board and the exposed
top metal is thermally connected to the power devices
and the power inductors. An external heat sink can be
applied to the top of the device for excellent heat sinking
with airflow. Basically all power dissipating devices are
mounted directly to the substrate and the top exposed
metal. This provides two low thermal resistance paths to
remove heat.
Figure 10 shows a temperature plot of the LTM4620A
with BGA heat sink and 200LFM airflow with ~5.3W of
internal dissipation.
Figure 11 shows a temperature plot of the LTM4620A with
no heat sink and 200LFM airflow with ~6.5W of internal
dissipation.
These plots equate to a paralleled 1.2V at 26A design, and
a 5V at 25A design operating from a 12V input.
Safety Considerations
The LTM4620A modules do not provide isolation from V_IN
to V_OUT. There is no internal fuse. If required, a slow blow
fuse with a rating twice the maximum input current needs
to be provided to protect each unit from catastrophic failure.
The fuse or circuit breaker should be selected to limit the
current to the regulator during overvoltage in case of an
internal top MOSFET fault. If the internal top MOSFET fails,
then turning it off will not resolve the overvoltage, thus
the internal bottom MOSFET will turn on indefinitely trying
to protect the load. Under this fault condition, the input
voltage will source very large currents to ground through
the failed internal top MOSFET and enabled internal bot-
tom MOSFET. This can cause excessive heat and board
damage depending on how much power the input voltage
can deliver to this system. A fuse or circuit breaker can
be used as a secondary fault protector in this situation.
Figure 10. LTM4620A 12V to 1.2V at 26A with 200LFM Air Flow
Figure 11. LTM4620A 12V to 5V at 25A with 200LFM Air Flow
24
For more information www.linear.com/LTM4620A
4620afb