LSN-T10-D12J Datasheet, PDF (5/12 Pages) Murata Manufacturing Co., Ltd. – Single Adjustable Output, Non-isolated, 12Vin, 10A, SIP, DC/DC Converters

LSN-T/10-D12
Single Adjustable Output, Non-isolated, 12Vin, 10A, SIP, DC/DC Converters
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 techniques
should be used. To prevent high frequency voltage differences between VOUT
and Sense, we recommend installation of a 1000pF capacitor close to the
converter.
The sense function is capable of compensating for voltage drops between the
+Output and +Sense pins that do not exceed 10% of VOUT.
[VOUT(+) – Common] – [Sense(+) – Common] ≤ 10%VOUT
Power derating (output current limiting) is based upon maximum output
current 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 LSN's specified rating. Therefore:
(VOUT at pins) x (IOUT) ≤ rated output power
The internal 10Ω 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: Connect the +Sense pin (pin 3) to +Output (pin 4) at the DC/DC con-
verter pins, if the sense function is not used for remote regulation.
On/Off Control
The On/Off Control pin may be used for remote on/off operation. LSN-T/10-D12
SIP is designed so they are enabled when the control pin is left open (internal
pull-down to Common) and disabled when the control pin is pulled high, as
shown in Figure 2 and 2a.
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Figure 2. Driving the On/Off Control Pin with an Open-Collector Drive Circuit
Dynamic control of the on/off function is best accomplished with a mechani-
cal relay or open-collector/open-drain drive circuit. The drive circuit should
be able to sink appropriate current when activated and withstand appropriate
voltage when deactivated.The on/off control function, however, can be exter-
nally inverted so that the converter will be disabled while the input voltage is
ramping up and then "released" once the input has stabilized.
LSN D12 SIP Series DC/DC converters do not incorporate output overvoltage
protection. In the extremely rare situation in which the device’s feedback loop
is broken, the output voltage may run to excessively high levels (VOUT = VIN). If
it is absolutely imperative that you protect your load against any and all possi-
ble overvoltage situations, voltage limiting circuitry must be provided external
to the power converter.
Output Overcurrent Detection
Overloading the output of a power converter for an extended period of time
will invariably cause internal component temperatures to exceed their maxi-
mum ratings and eventually lead to component failure. High-current-carrying
components such as inductors, FET's and diodes are at the highest risk. LSN
D12 SIP Series DC/DC converters incorporate an output overcurrent detection
and shutdown function that serves to protect both the power converter and its
load.
If the output current exceeds it maximum rating by typically 70% or if the
output voltage drops to less than 98% of it's original value, the LSN D12's
internal overcurrent-detection circuitry immediately turns off the converter,
which then goes into a "hiccup" mode. While hiccupping, the converter will
continuously attempt to restart itself, go into overcurrent, and then shut down.
Under these conditions, the average output current will be approximately
400mA. Once the output short is removed, the converter will automatically
restart itself.
Thermal Performance
The typical output-current thermal-derating curves shown below enable
designers to determine how much current they can reliably derive from each
model of the LSN D12 SIP's under known ambient-temperature and air-flow
conditions. Similarly, the curves indicate how much air flow is required to reli-
ably deliver a specific output current at known temperatures.
The highest temperatures in LSN D12 SIP's occur at their output inductor,
whose heat is generated primarily by I²R losses. The derating curves were
developed using thermocouples to monitor the inductor temperature and
varying the load to keep that temperature below +110°C under the assorted
conditions of air flow and air temperature. Once the temperature exceeds
+115°C (approx.), the thermal protection will disable the converter. Automatic
restart occurs after the temperature has dropped below +110°C.
Lastly, when LSN D12 SIP's are installed in system boards, they are obviously
subject to numerous factors and tolerances not taken into account here. If you
are attempting to extract the most current out of these units under demand-
ing temperature conditions, we advise you to monitor the output-inductor
temperature to ensure it remains below +110°C at all times.
Thermal Performance for "H" Models
Enhanced thermal performance can be achieved when LSN D12 SIP's are
mounted horizontally ("H" models) and the output inductor (with its electrically
isolating, thermally conductive pad installed) is thermally coupled to a copper
plane/pad (at least 0.55 square inches in area) on the system board. Your
conditions may vary, however our tests indicate this configuration delivers a
16°C to 22°C improvement in ambient operating temperatures.
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