LSN2-T/30-D12 Series

DOSA-SIP, 30A POL DC/DC Converters

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MDC_LSN2-T/30-D12 Series.B15 Page 5 of 17

Figure 3. Measuring Output Ripple/Noise (PARD)

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.

Input Fusing

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

inputs of power conversion components. The LSN2-T/30-D12 Series are not

internally fused. Therefore, if input fusing is mandatory, either a normal-blow

or a slow-blow fuse with a value no greater than twice the maximum input cur-

rent calculated at low line with the converter’s minimum efficiency should be

installed within the ungrounded input path to the converter.

Safety Considerations

LSN2-T/30-D12 SIPs are non-isolated DC/DC converters. In general, all DC/DC’s

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

tion requirements, in compliance with relevant safety-agency specifications

(usually UL/IEC/EN60950-1).

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

LSN2-T/30-D12 SIP Series DC/DCs 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

ing input voltage crosses the lower limit of the specified input voltage range

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.

Remote Sense

LSN2-T/30-D12 Series offer an output sense function. The sense function

enables point-of-use regulation for overcoming moderate IR drops in conduc-

tors 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 conse-

quently 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 techniques should be used.

recommend installation of a 1000pF capacitor close to the converter.

The sense function is capable of compensating for voltage drops between

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 functions

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

beyond the LSN2-T/30-D12’s specified rating. Therefore:

≤ rated output power

The internal 10.5

W 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

must be tied to +Output at the DC/DC converter pins.

Remote On/Off Control

Normally this input is controlled by the user’s external transistor or relay. With

simple external circuits, it may also be selected by logic outputs. Please note

however that the actual control threshold levels vary somewhat with the PWM

supply and therefore are best suited to “open collector” or “open drain” type

logic. The On/Off control takes effect only when appropriate input power has

been applied and stabilized (approximately 7msec).

For negative polarity, the default operation leaves this pin open (unconnected)

or LOW. The output will then always be on (enabled) whenever appropriate input

power is applied.

Dynamic control of the On/Off must be capable of sinking or sourcing the

control current (approximately 1mA max.) and not overdrive the input greater

activating the On/Off control. Be aware that a delay of several milliseconds

occurs (see specifications) between activation of the control and the resulting

change in the output.

C1

C1 = 1µF CERAMIC

C2 = 10µF TANTALUM

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

C2

COPPER STRIP

COPPER STRIP

SCOPE

+OUTPUT

COMMON

+SENSE