DC1307A Datasheet, PDF (15/22 Pages) Linear Technology – Complete Switch Mode Power Supply

Applications Information
LTM8027
V_OUT
AUX
BIAS1
SS
RUN
BIAS2
R_ADJ
C_OUT C_OUT
GND
C_IN
V_IN
R_T
GND
SYNC
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Figure 3. Suggested Layout
Ensure that the grounding and heat sinking are acceptable.
A few rules to keep in mind are:
1. Place the R_ADJ and R_T resistors as close as possible to
their respective pins.
2. Place the C_IN capacitor as close as possible to the V_IN
and GND connection of the LTM8027.
3. Place the C_OUT capacitor as close as possible to the
V_OUT and GND connection of the LTM8027.
4. Place the C_IN and C_OUT capacitors such that their
ground current flow directly adjacent to or underneath
the LTM8027.
5. Connect all of the GND connections to as large a copper
pour or plane area as possible on the top layer. Avoid
breaking the ground connection between the external
components and the LTM8027.
Use vias to connect the GND copper area to the board’s
internal ground planes. Liberally distribute these GND vias
to provide both a good ground connection and thermal
path to the internal planes of the printed circuit board. Pay
attention to the location and density of the thermal vias in
Figure 3. The LTM8027 can benefit from the heat sinking
afforded by vias that connect to internal GND planes at
these locations, due to their proximity to internal power
handling components. The optimum number of thermal
vias depends upon the printed circuit board design. For
example, a board might use very small via holes. It should
employ more thermal vias than a board that uses larger
holes.
Thermal Considerations
The LTM8027 output current may need to be derated if it
is required to operate in a high ambient temperature or
deliver a large amount of continuous power. The amount
of current derating is dependent upon the input voltage,
output power and ambient temperature. The temperature
rise curves given in the Typical Performance Character-
istics section can be used as a guide. These curves were
generated by a LTM8027 mounted to a 58cm² 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.
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