LTM8042EV-1PBF LINER [Linear Technology], LTM8042EV-1PBF Datasheet - Page 18

• Manufacturer Part Number: LTM8042EV-1PBF
• Description: ?Module Boost LED Driver and Current Source
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LTM8042/LTM8042-1
PCB Layout
Most of the headaches associated with PCB layout have
been alleviated or even eliminated by the high level of
integration of the LTM8042/LTM8042-1. The device is
nevertheless 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
specified operation with a haphazard or poor layout. See
Figures 2, 3 and 4 for suggested layouts of boost, buck
and buck-boost operating modes.
Ensure that the grounding and heat sinking are acceptable.
A few rules to keep in mind are:
1. Place the R
2. Place the C
3. Place the C
18
spective pins.
to the V
LTM8042-1.
BSTOUT/BKIN or BSTIN/BKLED
of the LTM8042/LTM8042-1.
IN
IN
OUT
and GND connections of the LTM8042/
T
and C
resistor as close as possible to its re-
capacitor as close as possible to the
VCC
capacitor as close as possible
THERMAL VIAS TO GROUND PLANE
GND
C
V
–
VCC
IN
and GND connection
Figure 2. Suggested Layout for Boost Operation
V
CC
BSTIN/BKLED
C
IN
–
GND
GND
C
4. Place the C
5. Connect all of the GND connections to as large a copper
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 Figures 2 through 4. The LTM8042/LTM8042-1
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.
OUT
TO LED STRING
ground current flows directly adjacent to or underneath
the LTM8042/LTM8042-1.
pour or plane area as possible on the top layer. Avoid
breaking the ground connection between the external
components and the LTM8042/LTM8042-1.
BSTOUT/BKIN
R
T
TG
IN
LED
LED
, C
+
+
VCC
80421 F02
TGEN
CTL
and C
OUT
capacitors such that their
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