ltm8027 Linear Technology Corporation, ltm8027 Datasheet - Page 15

• Manufacturer Part Number: ltm8027
• Description: 60v, 4a Dc/dc ?module Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
PCB Layout
Most of the headaches associated with PCB layout have
been alleviated or even eliminated by the high level of
integration of the LTM8027. The LTM8027 is neverthe-
less a switching power supply, and care must be taken to
minimize EMI and ensure proper operation. Even with the
high level of integration, you may fail to achieve specifi ed
operation with a haphazard or poor layout. See Figure 3
for a suggested layout.
Ensure that the grounding and heatsinking are acceptable.
A few rules to keep in mind are:
1. Place the R
2. Place the C
3. Place the C
4. Place the C
5. Connect all of the GND connections to as large a copper
their respective pins.
and GND connection of the LTM8027.
V
ground current fl ow directly adjacent to or underneath
the LTM8027.
pour or plane area as possible on the top layer. Avoid
breaking the ground connection between the external
components and the LTM8027.
OUT
and GND connection of the LTM8027.
ADJ
IN
OUT
IN
capacitor as close as possible to the V
and R
and C
capacitor as close as possible to the
T
OUT
resistors as close as possible to
capacitors such that their
RUN
SS
R
GND
ADJ
BIAS1
BIAS2
AUX
R
T
SYNC
Figure 3. Suggested Layout
IN
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 benefi t 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 Characteristics section
can be used as a guide. These curves were generated by a
LTM8027 mounted to a 58cm
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.
C
C
OUT
IN
C
OUT
V
GND
8027 F03
V
OUT
IN
2
4-layer FR4 printed circuit
LTM8027
15
8027f