LTM4600(RevA) Ver la hoja de datos (PDF) - Linear Technology
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LTM4600 Datasheet PDF : 24 Pages
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LTM4600
APPLICATIO S I FOR ATIO
In the application where the light load efficiency is im-
portant, tying the FCB pin above 0.6V threshold enables
discontinuous operation where the bottom MOSFET turns
off when inductor current reverses. Therefore, the conduc-
tion loss is minimized and light load efficient is improved.
The penalty is that the controller may skip cycle and the
output voltage ripple increases at light load.
Paralleling Operation with Load Sharing
Two or more LTM4600 modules can be paralleled to provide
higher than 10A output current. Figure 7 shows the neces-
sary interconnection between two paralleled modules. The
OPTI-LOOP™ current mode control ensures good current
sharing among modules to balance the thermal stress.
The new feedback equation for two or more LTM4600s
in parallel is:
VOUT
=
0.6V
•
100k
N
+
RSET
RSET
where N is the number of LTM4600s in parallel.
VIN
VIN
VOUT
VOUT
LTM4600
(20AMAX)
PGND COMP VOSET SGND
RSET
Thermal Considerations and Output Current Derating
The power loss curves in Figures 8 and 13 can be used
in coordination with the load current derating curves in
Figures 9 to 12, and Figures 14 to 15 for calculating an
approximate θJA for the module with various heatsink-
ing methods. Thermal models are derived from several
temperature measurements at the bench, and thermal
modeling analysis. Application Note 103 provides a detailed
explanation of the analysis for the thermal models, and the
derating curves. Tables 3 and 4 provide a summary of the
equivalent θJA for the noted conditions. These equivalent
θJA parameters are correlated to the measure values, and
improved with air-flow. The case temperature is maintained
at 100°C or below for the derating curves. This allows for
4W maximum power dissipation in the total module with
top and bottom heatsinking, and 2W power dissipation
through the top of the module with an approximate θJC
between 6°C/W to 9°C/W. This equates to a total of 124°C
at the junction of the device.
Safety Considerations
The LTM4600 modules do not provide isolation from VIN to
VOUT. There is no internal fuse. If required, a slow blow fuse
with a rating twice the maximum input current should be
provided to protect each unit from catastrophic failure.
COMP VOSET SGND
VIN
LTM4600 VOUT
PGND
4600 F07
Figure 7. Parallel Two µModules with Load Sharing
OPTI-LOOP is a trademark of Linear Technology Corporation.
4600fa
14
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