Datasheet
LTM8061
16
8061fa
For more information www.linear.com/LTM8601
Figure 8. Layout Showing Suggested External
Components, Power Planes and Thermal Vias
applicaTions inForMaTion
Most of the headaches associated with PCB layout have
been alleviated or even eliminated by the high level of
LTM8061 integration. The LTM8061 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 Figure 8
for a suggested layout. Ensure that the grounding and
heat sinking are acceptable.
1. Place the C
IN
capacitor as close as possible to the V
IN
and GND connection of the LTM8061.
2. If used, place the C
BAT
capacitor as close as possible
to the BAT and GND connection of the LTM8061.
3. Place the C
IN
and C
BAT
(if used) capacitors such that their
ground current flows directly adjacent or underneath
the LTM8061.
4. 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 LTM8061.
5. For good heat sinking, use vias to connect the GND cop
-
per 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 8. The LTM8061
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.
Hot-Plugging Safely
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LTM8061. However, these capacitors
can cause problems if the LTM8061 is plugged into a live
input supply (see Application Note 88 for a complete dis
-
cussion). The low loss ceramic capacitor combined with
stray inductance in series with the power source forms an
underdamped tank circuit, and the voltage at the V
IN
pin
of the LTM8061 can ring to more than twice the nominal
C
SS
C
BAT
BIAS
RNG/SS
NTC
TMR
V
IN
FAULT
CHRG
V
INC
/CLP
V
INA
GND
THERMAL VIAS
BAT
C
IN
(OPTIONAL)
(OPTIONAL)
RUN
CLP SENSE
RESISTOR
8061 F08