MQFL-270-09S Datasheet, PDF (12/17 Pages) SynQor Worldwide Headquarters – HIGH RELIABILITY DC-DC CONVERTER

Technical Specification
MQFL-270-09S
Output: _{9.0 V}
Current: _{13 A}
INPUT OVER-VOLTAGE SHUTDOWN: The MQFL converter
also has an over-voltage feature that ensures the converter will
be off if the input voltage is too high. It also has a hysteresis and
time delay to ensure proper operation.
CURRENT LIMIT: The converter will reduce its output voltage in
response to an overload condition. If the output voltage drops to
below approximately 50% of the nominal setpoint for longer than
1 second, the auto-restart feature will engage. The auto-restart
feature will stop the converter from delivering load current, in
order to protect the converter and the load from thermal damage.
After four seconds have elapsed, the converter will automatically
restart.
In a system with multiple converters configured for load sharing
using the SHARE pin, if the auto-restart feature engages,
the converters will synchronize their restart using signals
communicated on the SHARE pin.
BACK-DRIVE CURRENT LIMIT: Converters that use MOSFETs as
synchronous rectifiers are capable of drawing a negative current
from the load if the load is a source of short- or long-term energy.
This negative current is referred to as a “back-drive current”.
Conditions where back-drive current might occur include paralleled
converters that do not employ current sharing, or where the current
share feature does not adequately ensure sharing during the
startup or shutdown transitions. It can also occur when converters
having different output voltages are connected together through
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 page) 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 on the
figures page. 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 Figure 5. 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 adhe-
sive 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-270-09S
Phone [phone]
www.synqor.com
Doc.# 005-0005057 Rev. A
05/29/09
Page 12