LTM8032 datasheet(22/30 Pages) LINER

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LTM8003

8003fc

For more information www.linear.com/LTM8003

APPLICATIONS INFORMATION

diodes inside the LTM8003 can pull large currents from

the output through the VIN pin. Figure 4 shows a circuit

that runs only when the input voltage is present and that

protects against a shorted or reversed input.

LTM8003

VIN

8003 F04

RUN

Figure4. The Input Diode Prevents a Shorted Input from

Discharging a Backup Battery Tied to the Output. It Also

Protects the Circuit from a Reversed Input. The LTM8003 Runs

Only When the Input Is Present

PCB Layout

Most of the headaches associated with PCB layout have

been alleviated or even eliminated by the high level of

integration of the LTM8003. The LTM8003 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 5

for a suggested layout. Ensure that the grounding and

heat sinking are acceptable.

A few rules to keep in mind are:

1. Place CFF, RFB and RT 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 LTM8003.

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

VOUT and GND connection of the LTM8003.

4. Place the CIN and COUT capacitors such that their

ground current flow directly adjacent to or underneath

the LTM8003.

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 LTM8003.

6. 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 5. The LTM8003 can benefit from

theheat-sinkingaffordedbyviasthatconnecttointernal

GND planes at these locations, due to their proximity

to internal power handling components. The optimum

SYNC

GND

GND/ THERMAL VIAS

RUN

BIAS

VOUT

VIN

COUT

CIN

TR/SS

8003 F05

Figure5. Layout Showing Suggested External Components, GND Plane and Thermal Vias

LTM8032 Datasheet(PDF) 22 Page - Linear Technology

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