P

D

I

OUT

TPS79901-Q1, TPS79912-Q1, TPS79915-Q1

TPS79918-Q1, TPS79925-Q1, TPS79927-Q1, TPS79933-Q1

www.ti.com

SBVS097E

– MARCH 2008 – REVISED JANUARY 2012

Minimum Load

The TPS799xx is stable and well behaved with no output load. To meet the specified accuracy, a minimum load

of 500

μA is required. Below 500 μA at junction temperatures near 125°C, the output can drift up enough to

cause the output pulldown to turn on. The output pulldown limits voltage drift to 5% typically, but ground current

could increase by approximately 50

μA. In typical applications, the junction cannot reach high temperatures at

light loads since there is no appreciable dissipated power. The specified ground current would then be valid at no

load in most applications.

THERMAL INFORMATION

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 due to

overheating.

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

heatsink. For reliable operation, junction temperature should be limited 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 should

trigger at least 35

°C above the maximum expected ambient condition of your 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 TPS799xx has been designed to protect against overload conditions. It

was not intended to replace proper heatsinking. Continuously running the TPS799xx into thermal shutdown

degrades device reliability.

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. Using heavier copper increases the effectiveness in removing heat from the device. The

addition of plated through holes to heat-dissipating layers also improves the 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)

Package Mounting

Solder pad footprint recommendations for the TPS799xx are available from the Texas Instruments' web site at

www.ti.com.

Copyright

© 2008–2012, Texas Instruments Incorporated

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Product Folder Link(s): TPS79901-Q1 TPS79912-Q1 TPS79915-Q1 TPS79918-Q1 TPS79925-Q1 TPS79927-Q1

TPS79933-Q1