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Capacitor at VAUX

Layout Considerations

THERMAL INFORMATION

P

D(MAX)

+

T

J(MAX)

* T

A

R

q

JA

+ 125°C * 85°C

48.7

°C W

+ 820 mW

(6)

TPS61200

TPS61201

TPS61202

SLVS577B – MARCH 2007 – REVISED FEBRUARY 2008

Between the VAUX pin and GND a capacitor must be connected. This capacitor is used to maintain and filter the

control supply voltage. It is charged during startup and before the main output VOUT is turned on. To ensure

stable operation, using at least 0.1

µF is recommended. At output voltages below 2.5 V, the capacitance should

be in the range of 1

µF. Since this capacitor is also used as a snubber capacitor for the main switch, using a

ceramic capacitor with low ESR is important.

As for all switching power supplies, the layout is an important step in the design, especially at high peak currents

and high switching frequencies. If the layout is not carefully done, the regulator could show stability problems as

well as EMI problems. Therefore, use wide and short traces for the main current path and for the power ground

tracks. The input and output capacitor, as well as the inductor should be placed as close as possible to the IC.

Use a common ground node for power ground and a different one for control ground to minimize the effects of

ground noise. Connect these ground nodes at any place close to one of the ground pins of the IC.

The feedback divider should be placed as close as possible to the control ground pin of the IC. To lay out the

control ground, it is recommended to use short traces as well, separated from the power ground traces. This

avoids ground shift problems, which can occur due to superimposition of power ground current and control

ground current.

Implementation of integrated circuits in low-profile and fine-pitch surface-mount packages typically requires

special attention to power dissipation. Many system-dependent issues such as thermal coupling, airflow, added

heat sinks and convection surfaces, and the presence of other heat-generating components affect the

power-dissipation limits of a given component.

Three basic approaches for enhancing thermal performance are listed below.

• Improving the power dissipation capability of the PCB design

• Improving the thermal coupling of the component to the PCB

• Introducing airflow in the system

resistance of the 10-pin QFN 3

dissipation is about 820 mW. More power can be dissipated if the maximum ambient temperature of the

application is lower.

Copyright © 2007–2008, Texas Instruments Incorporated

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