ltm8062 Linear Technology Corporation, ltm8062 Datasheet - Page 16

• Manufacturer Part Number: ltm8062
• Description: Ltm8062 32vin, 2a ?module Power Tracking Battery Charger Features
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
LTM8062
to add an electrolytic bulk capacitor to the V
capacitor’s relatively high equivalent series resistance
damps the circuit and eliminates the voltage overshoot.
The extra capacitor improves low frequency ripple filter-
ing and can slightly improve the efficiency of the circuit,
though it is physically large.
Thermal Considerations
The thermal performance of the LTM8062 is given in the
Typical Performance Characteristics section. These curves
were generated by the LTM8062 mounted to a 58cm
4-layer FR4 printed circuit board. Boards of other sizes
and layer count can exhibit different thermal behavior, so
it is incumbent upon the user to verify proper operation
over the intended system’s line, load and environmental
operating conditions.
For increased accuracy and fidelity to the actual application,
many designers use FEA to predict thermal performance.
To that end, the Pin Configuration section of the data sheet
typically gives four thermal coefficients:
1. θ
2. θ
3. θ
4. θ
While the meaning of each of these coefficients may seem
to be intuitive, JEDEC has defined each to avoid confusion
and inconsistency. These definitions are given in JESD
51-12, and are quoted or paraphrased below:
1. θ
2. θ
16
tom of the product case.
product case.
circuit board.
thermal resistance measured in a one cubic foot sealed
enclosure. This environment is sometimes referred to as
“still air” although natural convection causes the air to
move. This value is determined with the part mounted to
a JESD 51-9 defined test board, which does not reflect
an actual application or viable operating condition.
with all of the component power dissipation flowing
through the bottom of the package. In the typical
μModule, the bulk of the heat flows out the bottom
JA
JCbottom
JCtop
JB
JA
JCbottom
: Thermal resistance from junction to ambient.
: Thermal resistance from junction to the printed
is the natural convection junction-to-ambient air
: Thermal resistance from junction to top of the
: Thermal resistance from junction to the bot-
is the junction-to-board thermal resistance
IN
net. This
2
3. θ
4. θ
The most appropriate way to use the coefficients is when
running a detailed thermal analysis, such as FEA, which
considers all of the thermal resistances simultaneously.
None of them can be individually used to accurately pre-
dict the thermal performance of the product, so it would
be inappropriate to attempt to use any one coefficient to
correlate to the junction temperature versus load graphs
given in the LTM8033 data sheet.
A graphical representation of these thermal resistances
is given in Figure 8.
The blue resistances are contained within the μModule,
and the green are outside.
The die temperature of the LTM8062 must be lower than
the maximum rating of 125°C, so care should be taken in
the layout of the circuit to ensure good heat sinking of the
LTM8062. The bulk of the heat flow out of the LTM8062
is through the bottom of the module and the LGA pads
into the printed circuit board. Consequently a poor printed
circuit board design can cause excessive heating, result-
ing in impaired performance or reliability. Please refer to
the PCB Layout section for printed circuit board design
suggestions.
of the package, but there is always heat flow out into
the ambient environment. As a result, this thermal re-
sistance value may be useful for comparing packages
but the test conditions don’t generally match the user’s
application.
power dissipation flowing through the top of the pack-
age. As the electrical connections of the typical μModule
are on the bottom of the package, it is rare for an ap-
plication to operate such that most of the heat flows
from the junction to the top of the part. As in the case
of θ
packages but the test conditions don’t generally match
the user’s application.
almost all of the heat flows through the bottom of the
μModule and into the board, and is really the sum of the
θ
part through the solder joints and through a portion of
the board. The board temperature is measured a speci-
fied distance from the package, using a two sided, two
layer board. This board is described in JESD 51-9.
JCtop
JB
JCbottom
is the junction-to-board thermal resistance where
JCbottom
is determined with nearly all of the component
and the thermal resistance of the bottom of the
, this value may be useful for comparing
8062f