MQFL-28V-2R5S Datasheet, PDF (14/19 Pages) SynQor Worldwide Headquarters – HIGH RELIABILITY DC-DC CONVERTER

Technical Specification
MQFL-28V-2R5S
Output: 2.5V
Current: 40A
either explicit or parasitic diodes that, while normally off, become
conductive during startup or shutdown. Finally, some loads, such
as motors, can return energy to their power rail. Even a load
capacitor is a source of back-drive energy for some period of time
during a shutdown transient.
To avoid any problems that might arise due to back-drive current,
the MQFL converters limit the negative current that the converter
can draw from its output terminals. The threshold for this back-drive
current limit is placed sufficiently below zero so that the converter
may operate properly down to zero load, but its absolute value
(see the Electrical Characteristics) is small compared to the
converter’s rated output current.
THERMAL CONSIDERATIONS: The suggested Power Derating
Curves for this converter as a function of the case temperature and
the maximum desired power MOSFET junction temperature are on
the figure pages. All other components within the converter are
cooler than its hottest MOSFET, which at full power is no more
than 20ºC higher than the case temperature directly below this
MOSFET.
The Mil-HDBK-1547A component derating guideline calls for a
maximum component temperature of 105ºC. The power derating
figure therefore has one power derating curve that ensures this
limit is maintained. It has been SynQor’s extensive experience
that reliable long-term converter operation can be achieved
with a maximum component temperature of 125ºC. In extreme
cases, a maximum temperature of 145ºC is permissible, but not
recommended for long-term operation where high reliability is
required. Derating curves for these higher temperature limits are
also included in the power derating figure. The maximum case
temperature at which the converter should be operated is 135ºC.
When the converter is mounted on a metal plate, the plate will
help to make the converter’s case bottom a uniform temperature.
How well it does so depends on the thickness of the plate and
on the thermal conductance of the interface layer (e.g. thermal
grease, thermal pad, etc.) between the case and the plate. Unless
this is done very well, it is important not to mistake the plate’s
temperature for the maximum case temperature. It is easy for
them to be as much as 5-10ºC different at full power and at high
temperatures. It is suggested that a thermocouple be attached
directly to the converter’s case through a small hole in the plate
when investigating how hot the converter is getting. Care must
also be made to ensure that there is not a large thermal resistance
between the thermocouple and the case due to whatever adhesive
might be used to hold the thermocouple in place.
INPUT SYSTEM INSTABILITY: This condition can occur
because any DC/DC converter appears incrementally as a
negative resistance load. A detailed application note titled
“Input System Instability” is available on the SynQor website
which provides an understanding of why this instability arises,
and shows the preferred solution for correcting it.
Product # MQFL-28V-2R5S
Phone [phone]
www.synqor.com
Doc.# 005-005-0005185 Rev. 1 04/21/09
Page 14