CIN

VIN

SW

GND

31

LM53602, LM53603

www.ti.com

SNVSAR0 – NOVEMBER 2016

Product Folder Links: LM53602 LM53603

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Copyright © 2016, Texas Instruments Incorporated

Layout Guidelines (continued)

Figure 46. Current Loops With Fast Transients

11.1.1 Ground and Thermal Plane Considerations

As mentioned in the Layout Guidelines, TI recommends using one of the middle layers as a solid ground plane.

A ground plane provides shielding for sensitive circuits and traces. It also provides a quiet reference potential for

the control circuitry. The AGND and PGND pins must be connected to the ground plane using vias right next to

the bypass capacitors. PGND pins are connected to the source of the internal low-side MOSFET switch. They

must be connected directly to the grounds of the input and output capacitors. The PGND net contains noise at

the switching frequency and may bounce due to load variations. The PGND trace, as well as PVIN and SW

traces, must be constrained to one side of the ground plane. The other side of the ground plane contains much

less noise and must be used for sensitive routes.

TI recommends providing adequate device heat sinking by using the exposed pad (EP) of the IC as the primary

thermal path. Use a minimum 4 × 4 array of 10-mil thermal vias to connect the EP to the system ground plane for

heat sinking. The vias must be evenly distributed under the exposed pad. Use as much copper as possible for

system ground plane on the top and bottom layers for the best heat dissipation. TI recommends using a four-

layer board with the copper thickness, starting from the top, as: 2 oz. / 1 oz. / 1 oz. / 2 oz. A four-layer board with

enough copper thickness and proper layout provides low current conduction impedance, proper shielding and

lower thermal resistance.

These resources provide additional important guidelines for thermal PCB design:

•

AN-2020 Thermal Design By Insight, Not Hindsight (SNVA419)

•

AN-1520 A Guide to Board Layout for Best Thermal Resistance for Exposed Pad Packages (SNVA183)

•

Semiconductor and IC Package Thermal Metrics (SPRA953)

•

Thermal Design made Simple with LM43603 and LM43602 (SNVA719)

•

PowerPAD™ Thermally Enhanced Package (SLMA002)

•

PowerPAD Made Easy (SLMA004)

•

Using New Thermal Metrics (SBVA025)