The most effective combination of external I/O capacitors will be a function

of your line voltage and source impedance, as well as your particular load and

layout conditions. Our Applications Engineers can recommend potential solu-

tions and discuss the possibility of our modifying a given device’s internal filter-

ing to meet your specific requirements. Contact our Applications Engineering

Group for additional details.

Input Fusing

Most applications and or safety agencies require the installation of fuses at

the inputs of power conversion components. LSM D5 Series DC/DC convert-

ers are not internally fused. Therefore, if input fusing is mandatory, either a

normal-blow or a fast-blow fuse with a value no greater than 15 Amps should

be installed within the ungrounded input path to the converter.

As a rule of thumb however, we recommend to use a normal-blow or slow-

blow fuse with a typical value of about twice the maximum input current,

calculated at low line with the converters minimum efficiency.

Safety Considerations

LSM D5 SMT's are non-isolated DC/DC converters. In general, all DC/DC's

must be installed, including considerations for I/O voltages and spacing/

separation requirements, in compliance with relevant safety-agency speci-

fications (usually UL/IEC/EN60950).

In particular, for a non-isolated converter's output voltage to meet SELV

(safety extra low voltage) requirements, its input must be SELV compliant.

If the output needs to be ELV (extra low voltage), the input must be ELV.

Input Overvoltage and Reverse-Polarity Protection

LSM D5 SMT Series DC/DC's do not incorporate either input overvoltage

or input reverse-polarity protection. Input voltages in excess of the specified

absolute maximum ratings and input polarity reversals of longer than "instan-

taneous" duration can cause permanent damage to these devices.

Start-Up Time

ramping input voltage crosses the lower limit of the specified input voltage

range (4.5 Volts) and the fully loaded output voltage enters and remains within

its specified accuracy band. Actual measured times will vary with input source

impedance, external input capacitance, and the slew rate and final value of

the input voltage as it appears to the converter.

On/Off Control with the nominal input voltage already applied to the converter.

The specification defines the interval between the time at which the converter

is turned on and the fully loaded output voltage enters and remains within its

specified accuracy band. See Typical Performance Curves.

Figure 3. Measuring Output Ripple/Noise (PARD)

Remote Sense

LSM D5 SMT Series DC/DC converters offer an output sense function on

pin 6. The sense function enables point-of-use regulation for overcoming

moderate IR drops in conductors and/or cabling. Since these are non-isolated

devices whose inputs and outputs usually share the same ground plane,

sense is provided only for the +Output.

The remote sense line is part of the feedback control loop regulating the

DC/DC converter’s output. The sense line carries very little current and

consequently requires a minimal cross-sectional-area conductor. As such, it

is not a low-impedance point and must be treated with care in layout and

cabling. Sense lines should be run adjacent to signals (preferably ground),

and in cable and/or discrete-wiring applications, twisted-pair or similar tech-

niques should be used. To prevent high frequency voltage differences between

the converter.

The sense function is capable of compensating for voltage drops between the

Power derating (output current limiting) is based upon maximum output cur-

rent and voltage at the converter's output pins. Use of trim and sense func-

tions can cause the output voltage to increase, thereby increasing output

power beyond the LSM's specified rating. Therefore:

≤ rated output power

The internal 10.5

Ω resistor between +Sense and +Output (see Figure 1)

serves to protect the sense function by limiting the output current flowing

through the sense line if the main output is disconnected. It also prevents

output voltage runaway if the sense connection is disconnected.

Note: If the sense function is not used for remote regulation, +Sense

(pin 6) must be tied to +Output (pin 4) at the DC/DC converter pins.

Output ripple/noise (also referred to as periodic and random deviations

or PARD) may be reduced below specified limits with the installation of

additional external output capacitors. Output capacitors function as true filter

elements and should be selected for bulk capacitance, low ESR, and appro-

priate frequency response. Any scope measurements of PARD should be

made directly at the DC/DC output pins with scope probe ground less than

0.5" in length.

C1

C1 = NA

C2 = 22μF TANTALUM

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

C2

6

4

COPPER STRIP

3

COPPER STRIP

SCOPE

+OUTPUT

COMMON

+SENSE

All external capacitors should have appropriate voltage ratings and be located

as close to the converters as possible. Temperature variations for all relevant

parameters should be taken into consideration.

LSM-10A D5 Models

www.murata-ps.com

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