LX1662/62A, LX1663/63A

PRODUCT DA T ABOOK 1996/1997

15

Copyright © 1999

Rev. 1.1 11/99

Pentium is a registered trademark of Intel Corporation.

Cyrix is a registered trademark and 6x86, Gx86 and M2 are trademarks of Cyrix Corporation. K6 is a trademark of AMD.

Power PC is a trademark of International Business Machines Corporation. Alpha is a trademark of Digital Equipment Corporation.

USING THE LX1662/63 DEVICES

LAYOUT GUIDELINES - THERMAL DESIGN

A great deal of time and effort were spent optimizing the thermal

design of the demo boards. Any user who intends to implement

an embedded motherboard would be well advised to carefully

read and follow these guidelines. If the FET switches have been

carefully selected, external heatsinking is generally not required.

However, this means that copper trace on the PC board must now

be used. This is a potential trouble spot; as much copper area as

possible must be dedicated to heatsinking the FET switches, and

the diode as well if a non-synchronous solution is used.

In our VRM module, heatsink area was taken from internal

ground and V

with VIAS to the power device tabs. The TO-220 and TO-263

cases are well suited for this application, and are the preferred

packages. Remember to remove any conformal coating from all

exposed PC traces which are involved in heatsinking.

General Notes

As always, be sure to provide local capacitive decoupling close to

the chip. Be sure use ground plane construction for all high-

frequency work. Use low ESR capacitors where justified, but be

alert for damping and ringing problems. High-frequency designs

demand careful routing and layout, and may require several

iterations to achieve desired performance levels.

Power Traces

To reduce power losses due to ohmic resistance, careful consid-

eration should be given to the layout of traces that carry high

currents. The main paths to consider are:

I Input power from 5V supply to drain of top MOSFET.

I Trace between top MOSFET and lower MOSFET or Schottky

diode.

I Trace between lower MOSFET or Schottky diode and

ground.

I Trace between source of top MOSFET and inductor, sense

resistor and load.

FIGURE 13 — Power Traces

Output

Input

5V or 12V

LX166x

All of these traces should be made as wide and thick as

possible, in order to minimize resistance and hence power losses.

It is also recommended that, whenever possible, the ground, input

and output power signals should be on separate planes (PCB

layers). See Figure 13 – bold traces are power traces.

C

Ensure that this 1µF capacitor is placed as close to the IC as

possible to minimize the effects of noise on the device.

Layout Assistance

Please contact Linfinity’s Applications Engineers for assistance

with any layout or component selection issues. A Gerber file

with layout for the most popular devices is available upon re-

quest.

Evaluation boards are also available upon request. Please

check Linfinity's web site for further application notes.

PRODUCTION DATA - Information contained in this document is proprietary to LinFinity, and is current as of publication date. This document

may not be modified in any way without the express written consent of LinFinity. Product processing does not necessarily include testing of

all parameters. Linfinity reserves the right to change the configuration and performance of the product and to discontinue product at any time.

RELA TED DEVICES

LX1664/1665 - Dual Output PWM for µProcessor Applications

LX1668 - Triple Output PWM for µProcessor Applications

LX1553 - PWM for 5V - 3.3V Conversion