PAQ Series

Up to 150W 29.8V Nom Output Quarter-Brick Isolated

DC-DC Converter with 2:1 Wide Input Range

MDC_PAQ Series.A02 Page 13 of 16

www.murata-ps.com/support

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.