LSN-10A D12 Models
Output Reverse Conduction
Single Output, Non-Isolated, 12V
IN
, 1-5V
OUT,
10A, DC/DC's in SIP Packages
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.
All but the last two DUT's were vertical-mount models, and the direction of air
flow was parallel to the unit in the direction from pin 11 to pin 1.
As you may deduce from the derating curves and observe in the efficiency
curves on the following pages, LSN D12 SIP's maintain virtually constant
efficiency from half to full load, and consequently deliver very impressive
temperature performance even if operating at full load.
Lastly, when LSN D12 SIP's are installed in system boards, they are obvi-
ously 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
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 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. See page 9
for thermal comparison of two horizontally mounted units.
Many DC/DC's 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 "freewheeling" or
"catch" FET biasing itself on and effectively becoming a short circuit.
LSN D12 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 D12 SIP's under known ambient-temperature and air-flow
conditions. Similarly, the curves indicate how much air flow is required to
reliably 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 I
2
R losses. The derating curves were
developed using thermocouples to monitor the inductor temperature and
Typical Performance Curves for LSN D12 SIP Series
LSN-1/10-D12
Efficiency vs. Line Voltage and Load Current
89
87
Output Current (Amps)
12
LSN-1/10-D12
Output Current vs. Ambient Temperature
(Vertical mount, air flow direction from pin 11 to pin 1)
10
Natural Convection
8
85
Efficiency (%)
83
100 lfm
6
V
IN
= 10.8V
81
200 lfm
4
V
IN
= 12V
79
2
V
IN
= 13.2V
77
75
1
2
3
4
5
6
7
8
9
10
Load Current (Amps)
0
–40
0
60
70
80
90
100
110
Ambient Temperature ( C)
www.murata-ps.com
Technical enquiries
email: sales@murata-ps.com, tel:
+1 508 339 3000
MDC_LSN10A-D12.B01
Page 6 of 12
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