Datasheet
LTM8040
14
8040fa
APPLICATION INFORMATION
Figure 6. Suggested Layout
LEDA
LED
STRING
GND
VIAS TO GND PLANE
SHDN
LPWR BIAS
ADJ
RT
PWM
V
IN
C
IN
8040 F06
Layout Hints
Most of the headaches associated with PCB layout have
been alleviated or even eliminated by the high level of
integration of the LTM8040. The LTM8040 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 6
for a suggested layout. Ensure that the grounding and heat
sinking are acceptable. A few rules to keep in mind are:
1. Place the C
IN
capacitor as close as possible to the V
IN
and GND connection of the LTM8040.
2. Connect all of the GND connections to as large a cop-
per pour or plane area as possible on the top layer.
Avoid breaking the ground connection between the
external components and the LTM8040.
3. Use vias to connect the GND copper area to the board’s
internal ground plane. Liberally distribute these GND
vias to provide both a good ground connection and
thermal path to the internal planes of the printed circuit
board.
4. If the application requires BIAS to be connected to the
input voltage potential, tie BIAS to V
IN
, but be careful
not to break up the ground plane.