LSN10A-D5 Datasheet, PDF (7/15 Pages) Murata Manufacturing Co., Ltd. – Non-Isolated, 5VIN, 1-3.8VOUT 10 Amp DC/DC In SIP Package

Single Output LSN-10A Models
Non-Isolated, 5VIN, 1-3.8VOUT
10 Amp DC/DC In SIP Package
A trimpot can be used to determine the value of a single fixed resistor
which can then be connected, as shown in Figure 4, between the Trim pin and
+Output to trim down the output voltage, or between the Trim pin and Common
to trim up the output voltage. Fixed resistors should have absolute TCR’s less
than 100ppm/°C to ensure stability.
+INPUT
COMMON
+OUTPUT
TRIM
COMMON
Trim
Down
LOAD
Trim Up
Note: Install either a fixed trim-up resistor or a fixed trim-down resistor
depending upon desired output voltage.
Figure 4. Trim Connections Using Fixed Resistors
The equations below can be used as starting points for selecting specific trim-
resistor values. Recall, untrimmed devices are guaranteed to be p1% accurate.
Adjustment beyond the specified ±10% adjustment range is not recom-
mended.
Model
LSN-1/10-D5
LSN-1.2/10-D5
LSN-1.5/10-D5
LSN-1.8/10-D5
LSN-2/10-D5
LSN-2.5/10-D5
LSN-3.3/10-D5
LSN-3.8/10-D5
Trim Equations
1.62(VO – 0.8)
RT_DOWN (k7) =
1 – VO
–1
1.296
RTUP (k7) = _{VO – 1} – 1
2.49(VO – 0.8)
RT_DOWN (k7) =
1.2 – VO
– 2.37
1.992
RTUP (k7) = _{VO – 1.2} – 2.37
2.37(VO – 0.8)
RT_DOWN (k7) =
VO _NOM – VO
– 4.99
1.896
RTUP (k7) = _{VO – VO NOM} – 4.99
7.5(VO – 0.8)
RT_DOWN (k7) = _{VO NOM – VO}
– 4.99
6
RTUP (k7) =
– 4.99
VO – VO _NOM
7.5(VO – 0.8)
RT_DOWN (k7) =
3.8 – VO
– 13
RTUP (k7) =
6
VO – 3.8
– 13
Note: Resistor values are in k7. Accuracy of adjustment is subject to
tolerances of resistors and factory-adjusted, initial output accuracy.
VO = desired output voltage. VONOM = nominal output voltage.
Output Reverse Conduction
Many DC/DC converters using synchronous rectification suffer from Output
Reverse Conduction. If those devices have a voltage applied across their output
before a voltage is applied to their input (this typically occurs when another
power supply starts before them in a power-sequenced application), they will
either fail to start or self destruct. In both cases, the cause is the "freewheel-
ing" or "catch" FET biasing itself on and effectively becoming a short circuit.
LSN D5 SIP DC/DC converters are not damaged from Output Reverse
Conduction. They employ proprietary gate drive circuitry which makes them
immune to applied voltages during the startup sequence. If you are using
an external power source paralleled with the LSN, be aware that during the
start up phase, some low impedance condition or transient current may be
absorbed briefly into the LSN output terminals before voltage regulation is fully
established. You should insure that paralleled external power sources are not
disrupted by this condition during LSN start up.
Thermal Considerations and Thermal Protection
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 D5 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 required output current at known temperatures.
The highest temperatures in LSN D5 SIP's occur at their output inductor,
whose heat is generated primarily by I²R losses. The above curves were devel-
oped 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.
In all cases below, the DUT's were vertical-mount models, and the direction
of air flow was parallel to the unit in the direction from pin 1 to pin 11.
As you may deduce from the above curves and can observe in the efficiency
curves on the next page, LSN D5 SIP's are more efficient at lower current
levels. Also, I²R losses in the output inductor are significantly less at lower
currents. Consequently, LSN D5 SIP's deliver very impressive temperature
performance if operating at less than full load.
Lastly, when LSN D5 SIP's are installed in system boards, they are obviously
subject to numerous factors and tolerances not taken into account above.
If you are attempting to extract the most current out of these units under
demanding 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 D5 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 con-
ditions may vary, however our tests indicate this configuration delivers a 16°C
to 22°C improvement in ambient operating temperatures.
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