P

D

+ VIN*VOUT @ IOUT

TPS799L54, TPS799L57

www.ti.com

SBVS191B – APRIL 2012 – REVISED AUGUST 2014

10 Layout

10.1 Layout Guidelines

10.1.1 Board Layout Recommendations to Improve PSRR and Noise Performance

To improve ac performance (such as PSRR, output noise, and transient response), design the board with

separate ground planes for VIN and VOUT, with each ground plane connected only at the GND pin of the device.

In addition, connect the bypass capacitor directly to the GND pin of the device.

10.1.2 Thermal Information

10.1.2.1 Thermal Protection

Thermal protection disables the output when the junction temperature rises to approximately 165°C, allowing the

device to cool. When the junction temperature cools to approximately 145°C the output circuitry is again enabled.

Depending on power dissipation, thermal resistance, and ambient temperature, the thermal protection circuit may

cycle on and off. This cycling limits the dissipation of the regulator, protecting it from damage resulting from

overheating.

Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate

heatsink. For reliable operation, limit junction temperature to 125°C maximum. To estimate the margin of safety

in a complete design (including heatsink), increase the ambient temperature until the thermal protection is

triggered; use worst-case loads and signal conditions. For good reliability, thermal protection triggers at least

35°C above the maximum expected ambient condition of a particular application. This configuration produces a

worst-case junction temperature of 125°C at the highest expected ambient temperature and worst-case load.

The internal protection circuitry of the TPS799Lxx is designed to protect against overload conditions. This

circuitry is not intended to replace proper heatsinking. Continuously running the device into thermal shutdown

degrades device reliability.

10.1.2.2 Power Dissipation

The ability to remove heat from the die is different for each package type, presenting different considerations in

the PCB layout. The PCB area around the device that is free of other components moves the head from the

device to the ambient air. Performance data for JEDEC low- and high-K boards are given in the Thermal

Information table near the front of this data sheet. Using heavier copper increases the effectiveness in removing

heat from the device. The addition of plated through-holes to heat-dissipating layers also improves heatsink

effectiveness.

Power dissipation depends on input voltage and load conditions. Power dissipation is equal to the product of the

output current times the voltage drop across the output pass element, as shown in Equation 2:

(2)

10.1.2.3 Package Mounting

Solder pad footprint recommendations for the TPS799Lxx are available from the Texas Instruments' web site at

www.ti.com.

Copyright © 2012–2014, Texas Instruments Incorporated

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Product Folder Links: TPS799L54 TPS799L57