LTM8061 datasheet(16/20 Pages) LINER

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LTM8061

8061f

Figure 8. Layout Showing Suggested External

Components, Power Planes and Thermal Vias

APPLICATIONS INFORMATION

PCB Layout

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 CIN capacitor as close as possible to the VIN

and GND connection of the LTM8061.

2. If used, place the CBAT capacitor as close as possible

to the BAT and GND connection of the LTM8061.

3. Place the CINandCBAT(ifused)capacitorssuchthattheir

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 VIN pin

CSS

CBAT

VIN

VINC/CLP

VINA

GND

THERMAL VIAS

BAT

CIN

(OPTIONAL)

RUN

CLP SENSE

RESISTOR

8061 F08

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