LTM8027EVPBF datasheet(15/20 Pages) LINER

15 / 20 page

LTM8027

8027f

APPLICATIONS INFORMATION

PCB Layout

Most of the headaches associated with PCB layout have

been alleviated or even eliminated by the high level of

integration of the LTM8027. The LTM8027 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 speciﬁed

operation with a haphazard or poor layout. See Figure 3

for a suggested layout.

Ensure that the grounding and heatsinking are acceptable.

A few rules to keep in mind are:

1. Place the RADJ and RT resistors as close as possible to

their respective pins.

2. Place the CIN capacitor as close as possible to the VIN

and GND connection of the LTM8027.

3. Place the COUT capacitor as close as possible to the

VOUT and GND connection of the LTM8027.

4. Place the CIN and COUT capacitors such that their

ground current ﬂow directly adjacent to or underneath

the LTM8027.

5. 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 LTM8027.

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

Figure 3. The LTM8027 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.

Thermal Considerations

The LTM8027 output current may need to be derated if it is

required to operate in a high ambient temperature or deliver

a large amount of continuous power. The amount of current

derating is dependent upon the input voltage, output power

and ambient temperature. The temperature rise curves

given in the Typical Performance Characteristics section

can be used as a guide. These curves were generated by a

LTM8027 mounted to a 58cm2 4-layer FR4 printed circuit

board. Boards of other sizes and layer count can exhibit

different thermal behavior, so it is incumbent upon the user

to verify proper operation over the intended system’s line,

load and environmental operating conditions.

VOUT

VIN

GND

8027 F03

GND

RADJ

RUN

SYNC

AUX

BIAS1

BIAS2

CIN

COUT

Figure 3. Suggested Layout

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