lt3663 Linear Technology Corporation, lt3663 Datasheet - Page 9

• Manufacturer Part Number: lt3663
• Description: 1.2a, 1.5mhz Step-down Switching Regulator With Output Current Limit
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
PCB Layout
Proper operation and minimum EMI, requires careful
printed circuit board layout. Figure 5 shows the recom-
mended component placement with trace, ground plane
and via locations. Note that large, switched currents fl ow
in the LT3663’s V
and the input capacitor (C1). Keep the loop formed by
these components as small as possible and tied to sys-
tem ground in only one place. Locate these components,
along with the inductor and output capacitor, on the same
side of the circuit board, and keep their connections on
that layer. Place a local, unbroken ground plane below
these components, and tie this ground plane to system
ground at one location, ideally at the ground terminal of
the output capacitor C1. Make the SW and BOOST nodes
as small as possible. Include vias near the exposed GND
pad of the LT3663 to help remove heat from the LT3663
to the ground plane.
High Temperature Considerations
The die temperature of the LT3663 must not exceed the
maximum rating of 125°C. This is generally not a concern
IN
and SW pins, the catch diode (D2)
V
RUN
IN
R1
R2
Figure 5. LT3663 PCB Layout
C1
4
1
2
3
R
ILIM
LT3663
GND
unless the ambient temperature is above 85°C. For higher
temperatures, take care in the layout of the circuit to ensure
good heat sinking of the LT3663. De-rate the maximum
load current as the ambient temperature approaches
125°C. Calculate the die temperature by multiplying the
LT3663 power dissipation by the thermal resistance from
junction to ambient. Estimate the power dissipation within
the LT3663 by calculating the total power loss from an
effi ciency measurement and subtracting the catch diode
loss. Thermal resistance depends on the layout of the
circuit board, but 64°C/W is typical for the (2mm × 3mm)
DFN (DCB) package.
Other Linear Technology Publications
Application Notes 19, 35 and 44 contain more detailed
descriptions and design information for Buck regulators
and other switching regulators. The LT1376 data sheet
has a more extensive discussion of output ripple, loop
compensation and stability testing. Design Note 100
shows how to generate a bipolar output supply using a
Buck regulator.
C2
8
7
6
5
D1
C3
V
OUT
3663 F05
L
LT3663
3663fa
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