PAQ Datasheet, PDF (13/16 Pages) Murata Manufacturing Co., Ltd. – Up to 150W 29.8V Nom Output Quarter-Brick Isolated DC-DC Converter with 2:1 Wide Input Range

PAQ Series
Up to 150W 29.8V Nom Output Quarter-Brick Isolated
DC-DC Converter with 2:1 Wide Input Range
Floating Outputs
Since these are isolated DC/DC converters, their outputs are “floating” with
respect to their input. The essential feature of such isolation is ideal ZERO
CURRENT FLOW between input and output. Real-world converters however do
exhibit tiny leakage currents between input and output (see Specifications).
These leakages consist of both an AC stray capacitance coupling component
and a DC leakage resistance. When using the isolation feature, do not allow
the isolation voltage to exceed specifications. Otherwise the converter may
be damaged. Designers will normally use the negative output (-Output) as
the ground return of the load circuit. You can however use the positive output
(+Output) as the ground return to effectively reverse the output polarity.
Minimum Output Loading Requirements
These converters employ a synchronous rectifier design topology. All models
regulate within specification and are stable under no load to full load conditions.
Operation under no load might however slightly increase output ripple and noise.
Thermal Shutdown
To protect against thermal over-stress, these converters include thermal shut-
down circuitry. If environmental conditions cause the temperature of the DC/
DC’s to rise above the Operating Temperature Range up to the shutdown tem-
perature, an on-board electronic temperature sensor will power down the unit.
When the temperature decreases below the turn-on threshold, the converter
will automatically restart. There is a small amount of hysteresis to prevent
rapid on/off cycling. CAUTION: If you operate too close to the thermal limits, the
converter may shut down suddenly without warning. Be sure to thoroughly test
your application to avoid unplanned thermal shutdown.
Temperature Derating Curves
The graphs in this data sheet illustrate typical operation under a variety of condi-
tions. The Derating curves show the maximum continuous ambient air temperature
and decreasing maximum output current which is acceptable under increasing
forced airflow measured in Linear Feet per Minute (“LFM”). Note that these are
AVERAGE measurements. The converter will accept brief increases in temperature
and/or current or reduced airflow as long as the average is not exceeded.
Note that the temperatures are of the ambient airflow, not the converter itself
which is obviously running at higher temperature than the outside air. Also note
that “natural convection” is defined as very low flow rates which are not using
fan-forced airflow. Depending on the application, “natural convection” is usu-
ally about 30-65 LFM but is not equal to still air (0 LFM).
Murata Power Solutions makes Characterization measurements in a closed
cycle wind tunnel with calibrated airflow. Both thermocouples and an infrared
camera system are used to observe thermal performance. Sometimes it is
possible to estimate the effective airflow if you thoroughly understand the
enclosure geometry, entry/exit orifice areas and the fan flowrate specifications.
CAUTION: If these Derating guidelines are exceeded, the converter may have
an unplanned Over Temperature shut down. Also, these graphs are all collected
near Sea Level altitude. Be sure to reduce the derating for higher altitude.
Output Overvoltage Protection (OVP)
This converter monitors its output voltage for an over-voltage condition using
an on-board electronic comparator. If the output exceeds OVP limits, the sens-
ing circuit will power down the unit, and the output voltage will decrease. After
a time-out period, the PWM will automatically attempt to restart, causing the
output voltage to ramp up to its rated value. It is not necessary to power down
and reset the converter for this automatic OVP-recovery restart.
If the fault condition persists and the output voltage climbs to excessive levels,
the OVP circuitry will initiate another shutdown cycle. This on/off cycling is
referred to as “hiccup” mode.
Current Limiting (Power limit with current mode control)
As power demand increases on the output and enters the specified “limit
inception range” limiting circuitry activates in the DC-DC converter to limit/
restrict the maximum current or total power available. Once the current
reaches a certain range the output voltage will start to decrease while the
output current continues to increase, thereby maintaining constant power, until
a minimum voltage set is reached and the converter enters a “hiccup” (on off
cycling) mode of operation until the load is reduced below the threshold level,
whereupon it will return to a normal mode of operation. Current limit inception
is defined as the point where the output voltage has decreased by a pre-speci-
fied percentage (usually a 2% decrease from nominal).
Short Circuit Condition (Current mode control)
The short circuit condition is an extension of the “Current Limiting” condition.
When the monitored peak current signal reaches a certain range, the PWM
controller’s outputs are shut off thereby turning the converter “off.” This is
followed by an extended time out period. This period can vary depending on
other conditions such as the input voltage level. Following this time out period,
the PWM controller will attempt to re-start the converter by initiating a “normal
start cycle” which includes softstart. If the “fault condition” persists, another
“hiccup” cycle is initiated. This “cycle” can and will continue indefinitely until
such time as the “fault condition” is removed, at which time the converter will
resume “normal operation.” Operating in the “hiccup” mode during a fault
condition is advantageous in that average input and output power levels are
held low preventing excessive internal increases in temperature.
Trimming Output Voltage
PAQ converters have a trim capability that enables users to adjust the output
voltage from +10% to –20% (refer to the trim equations). Adjustments to the
output voltage can be accomplished with a single fixed resistor as shown in
Figures 4 and 5. A single fixed resistor can increase or decrease the output
voltage depending on its connection. Resistors should be located close to
the converter and have TCR’s less than 100ppm/°C to minimize sensitivity
to changes in temperature. If the trim function is not used, leave the trim pin
open.
Standard PAQ’s have a “positive trim” where a single resistor connected from
the Trim pin to the +Sense will increase the output voltage. A resistor con-
nected from the Trim Pin to the –Sense will decrease the output voltage.
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MDC_PAQ Series.A02 Page 13 of 16