MPDTH_50 Series.A08 Page 6 of 6

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MPDTH***50 Series

Adjustable Non-isolated 6-Amp

POLA DC/DC Converters

Murata Power Solutions, Inc. makes no representation that the use of its products in the circuits described herein, or the use of other

technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained herein do not imply

the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifications are subject to change without

notice.

© 2009 Murata Power Solutions, Inc.

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04/06/09

APPLICATION NOTES

Tracking Input

When enabled, the tracking function allows the output to follow an external

analog signal presented at the Tracking input. This pin becomes active

approximately 50 mS after the input voltage has been applied and the con-

verter reaches regulation. External track inputs must be referred to Ground.

Several converters may be Tracked in parallel to generate outputs which rise

and fall together.

The Tracking input range is zero Volts up to the nominal set-point output

voltage. If the Tracking input rises above the Vout nominal voltage, Vout will

remain at the set point after the power up ramp. If Track is unused, it should

be connected to +Vin.

Please note that because of the Under Voltage input lockout feature (UVLO),

the output cannot follow Track In during power up.

Over-Current Output Protection

If excess current is drawn from the converter, the output will shut down

and then periodically attempt to restart with narrow full power cycles. If the

excess load is reduced to within the rated maximum load, the converter

will immediately restart and operate normally. If the load is still too great,

another power-down cycle will begin. This is called “hiccup” operation. It

significantly reduces the output power to avoid damage. The converter will

quickly and automatically recover once the load is reduced.

Pre-Bias Operation

The MPDTHxx050 series of converters use synchronous rectification in

their output circuits. Normally, synchronous rectification may cause excess

current being sunk back in to the converter if there is higher external output

voltage present. If such prebias voltage is present on the output at the time

of startup, the converter will operate in a manner which avoids excessive

reverse current being sourced back into the output. This pre-bias protection

will continue until the converter achieves normal regulation at its set-point

output voltage.

In order to achieve successful pre-bias voltage protection, several conditions

must be met:

[1] The pre-bias voltage must be lower than the expected final set-point

output voltage. If the pre-bias voltage remains higher than the set-point

and is capable of back-driving excess current, possible output damage may

occur. If the pre-bias voltage has high impedance or has very limited current

capability, normal startup will proceed.

[2] Tracking operation must not be used during pre-bias startup. The Track-

ing input should be either open or connected to Vin so that normal soft start

will proceed. After successful startup of approximately 50 mSec, Tracking

may be resumed.

[3] Carefully examine any output circuits with large external output capaci-

tors and low-ESR. If there is no bleeder circuit or other method to reduce the

stored voltage AND the cap voltage is higher than the expected set-point,

operation may fail or the output may be damaged. Smaller capacitors with

lower energy storage should not interfere with startup. See the recom-

mended Connection Diagram. Use only as much output capacitance as

needed.

Also be careful immediately turning the converter back on after the Inhibit

control turns the converter off. Any energy stored in larger output capacitors

may cause the problems described above.