For best performance, we recommend installing a low-ESR capacitor

immediately adjacent to the converter’s input terminals. The capacitor

should be a ceramic type such as the Murata GRM32 series or a polymer

type. Initial suggested capacitor values are 10 to 22 μF, rated at twice the

expected maximum input voltage. Make sure that the input terminals do

not go below the undervoltage shutdown voltage at all times. More input

bulk capacitance may be added in parallel (either electrolytic or tantalum)

if needed.

Recommended Output Filtering

The converter will achieve its rated output ripple and noise with no

additional external capacitor. However, the user may install more exter-

nal output capacitance to reduce the ripple even further or for improved

dynamic response. Again, use low-ESR ceramic (Murata GRM32 series)

or polymer capacitors. Initial values of 10 to 47 μF may be tried, either

single or multiple capacitors in parallel. Mount these close to the converter.

Measure the output ripple under your load conditions.

Use only as much capacitance as required to achieve your ripple and

noise objectives. Excessive capacitance can make step load recovery

sluggish or possibly introduce instability. Do not exceed the maximum rated

output capacitance listed in the specifications.

Input Ripple Current and Output Noise

All models in this converter series are tested and specified for input

reflected ripple current and output noise using designated external input/

output components, circuits and layout as shown in the figures below. The

Cbus and Lbus components simulate a typical DC voltage bus. Please note

that the values of Cin, Lbus and Cbus will vary according to the specific

converter model.

In figure 5, the two copper strips simulate real-world printed circuit

impedances between the power supply and its load. In order to minimize

circuit errors and standardize tests between units, scope measurements

should be made using BNC connectors or the probe ground should not

exceed one half inch and soldered directly to the test circuit.

+INPUT

-INPUT

CURRENT

PROBE

TO

OSCILLOSCOPE

+

–

+

–

Figure 4: Measuring Input Ripple Current

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.

Temperature Derating Curves

The graphs in the next section 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 accept-

able 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 very low flow rates (below about 25 LFM) are similar to

“natural convection”, that is, not using fan-forced airflow.

Murata Power Solutions makes Characterization measurements in a

closed cycle wind tunnel with calibrated airflow. We use both thermocou-

ples and an infrared camera system to observe thermal performance.

CAUTION: These graphs are all collected at slightly above Sea Level

altitude. Be sure to reduce the derating for higher density altitude.

C1

C1 = 1μF CERAMIC

C2 = 10μF CERAMIC

LOAD 2-3 INCHES (51-76mm) FROM MODULE

C2

COPPER STRIP

COPPER STRIP

SCOPE

+OUTPUT

-OUTPUT

Figure 5: Measuring Output Ripple and Noise (PARD)

OKL-T/1-W12 Series

Programmable Output 1-Amp iLGA SMT PoLs

www.murata-ps.com

email: sales@murata-ps.com

04 Mar 2011

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