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OKX-T

OKX T/10 & T/16-D12 Series / Adjustable DOSA 10/16-Amp SIP DC/DC Converters

Murata Power Solutions 

OKX T/10 & T/16-D12 Series

Adjustable DOSA 10/16-Amp SIP DC/DC Converters

Minimum Output Loading Requirements

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 prevent many over temperature problems and damage, these converters

include thermal shutdown circuitry. If environmental conditions cause the

temperature of the DC/DC’s to rise above the Operating Temperature Range

up to the shutdown temperature, 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

temperature hysteresis to prevent rapid on/off cycling. The temperature sensor

is typically located adjacent to the switching controller, approximately in the

center of the unit. See the Performance and Functional Specifications.

CAUTION: If you operate too close to the thermal limits, the converter may

shut down suddenly without warning. Be sure to thoroughly test your applica-

tion to avoid unplanned thermal shutdown.

Temperature Derating Curves

The graphs in this data sheet illustrate typical operation under a variety of

conditions. 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 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 flow rates which are not

using fan-forced airflow. Depending on the application, “natural convection” is

usually 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. We use both thermocouples and an

infrared camera system to observe thermal performance.

CAUTION: If you routinely or accidentally exceed these Derating guidelines,

the converter may have an unplanned Over Temperature shut down. Also, these

graphs are all collected at slightly above Sea Level altitude. Be sure to reduce

the derating for higher density altitude.

Output Fusing

The converter is extensively protected against current, voltage and temperature

extremes. However your output application circuit may need additional protec-

tion. In the extremely unlikely event of output circuit failure, excessive voltage

could be applied to your circuit. Consider using an appropriate fuse in series

with the output.

Output Current Limiting

As soon as the output current increases to approximately 125% to 150% of

its maximum rated value, the DC/DC converter will enter a current-limiting

mode. The output voltage will decrease proportionally with increases in output

current, thereby maintaining a somewhat constant power output. This is also

commonly referred to as power limiting.

Current limiting inception is defined as the point at which full power falls

below the rated tolerance. See the Performance/Functional Specifications.

Note particularly that the output current may briefly rise above its rated value

in normal operation as long as the average output power is not exceeded. This

enhances reliability and continued operation of your application. If the output

current is too high, the converter will enter the short circuit condition.

Output Short Circuit Condition

When a converter is in current-limit mode, the output voltage will drop as the

output current demand increases. If the output voltage drops too low (approxi-

mately 98% of nominal output voltage for most models), the PWM controller

will shut down. Following a time-out period, the PWM will restart, causing the

output voltage to begin ramping up to its appropriate value. If the short-circuit

condition persists, another shutdown cycle will initiate. This rapid on/off cycling

is called “hiccup mode”. The hiccup cycling reduces the average output cur-

rent, thereby preventing excessive internal temperatures and/or component

damage. A short circuit can be tolerated indefinitely.

Remote Sense Input

The Sense input is normally connected at the load for the respective Sense

polarity (+Sense to the +Vout load). Sense inputs compensate for voltage drops

along the output wiring such as moderate IR drops and the current carrying

capacity of PC board etch. This output drop (the difference between Sense and

Vout when measured at the converter) should not exceed 0.5V. Use heavier

connections if this drop is excessive. Sense inputs also improve the stability of

the converter and load system by optimizing the control loop phase margin.

If the Sense function is not used for remote regulation, the user should con-

nect the Sense to their respective Vout at the converter pins.

Sense lines on the PCB should run adjacent to DC signals, preferably

Ground. Any long, distributed wiring and/or significant inductance introduced

into the Sense control loop can adversely affect overall system stability. If in

doubt, test your applications by observing the converter’s output transient

response during step loads. There should not be any appreciable ringing or

oscillation.

You may also adjust the output trim slightly to compensate for voltage loss

in any external filter elements. Do not exceed maximum power ratings. Exces-

sive voltage differences between Vout and Sense together with trim adjustment

of the output can cause the overvoltage protection circuit to activate and shut

down the output.

Power derating of the converter is based on the combination of maximum

output current and the highest output voltage at the ouput pins. Therefore the

designer must insure:

(Vout at pins) x (Iout) ≤ (Max. rated output power)

www.murata-ps.com/support

MDC_OKX2_T10T16.B06 Page 15 of 16

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