LTM4600HV
15
4600hvfe
For more information www.linear.com/LTM4600HV
explanation of the analysis for the thermal models, and the
derating curves. Tables 3 and 4 provide a summary of the
equivalent θ
JA
for the noted conditions. These equivalent
θ
JA
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 heat sinking, and 2W power dissipation
through the top of the module with an approximate θ
JC
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 LTM4600HV modules do not provide isolation from V
IN
to V
OUT
. 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.
Layout Checklist/Example
The high integration of the LTM4600HV makes the PCB
board layout very simple and easy. However, to optimize
its electrical and thermal performance, some layout con
-
siderations are still necessary.
• Use
large PCB copper areas for high current path, in-
cluding V
IN
, PGND and V
OUT
. It helps to minimize the
PCB conduction loss and thermal stress
• Place high frequency ceramic input and output capaci
-
tors next to the V
IN
, PGND and V
OUT
pins to minimize
high frequency noise
• Place a dedicated power ground layer underneath
the unit
• To minimize the via conduction loss and reduce module
thermal stress, use multiple vias for interconnection
between top layer and other power layers
• Do not put vias directly on pad unless they are capped.
• Use a separated SGND ground copper area for com
-
ponents connected to signal pins. Connect the SGND
to PGND underneath the unit
Figure 20 gives a good example of the recommended layout.
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 efficiency 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
Tw o or more LTM4600HV modules can be paralleled to
provide higher than 10A output current. Figure 7 shows
the necessary interconnection between two paralleled
modules. The OPTI
-LOOP™ current
mode control ensures
good current sharing among modules to balance the ther-
mal stress
. The new feedback equation for two or more
LTM4600HVs in parallel is:
V
OUT
= 0.6V •
N
+R
SET
R
SET
where N is the number of LTM4600HVs in parallel.
Figure 7. Parallel Tw o µModules with Load Sharing
V
IN
V
OUT
V
IN
V
OUT
(20A
MAX
)
4600hv F07
LTM4600HV
PGND SGNDCOMP
V
OSET
R
SET
V
IN
V
OUT
LTM4600HV
PGND
SGNDCOMP V
OSET
Thermal Considerations and Output Current Derating
The power loss curves in Figures 8 and 15 can be used
in coordination with the load current derating curves in
Figures 9 to 14, and Figures 16 to 19 for calculating an
approximate θ
JA
for the module with various heat sink-
ing methods. Thermal models are derived from several
temperature
measurements at the bench, and thermal
modeling analysis. Application Note 103 provides a detailed
applicaTions inForMaTion
