TPS2010, TPS2011, TPS2012, TPS2013

POWER-DISTRIBUTION

SLVS097A – DECEMBER 1994 – REVISED AUGUST 1995

16

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

power dissipation and junction temperature

The low on resistance of the N-channel MOSFET allows small surface-mount packages, such as SOIC or

TSSOP to pass large currents. The thermal resistances of these packages are high compared to that of power

packages; it is good design practice to check power dissipation and junction temperature. The first step is to

find ron at the input voltage and operating temperature. As an initial estimate, use the highest operating ambient

temperature of interest and read ron from Figure 23. Next calculate the power dissipation using:

P

D +

ron

I2

Finally, calculate the junction temperature:

T

J +

P

D

RqJA ) TA

Where:

TA = Ambient temperature

RθJA = Thermal resistance SOIC = 172°C/W, TSSOP = 179°C/W

Compare the calculated junction temperature with the initial estimate. If they do not agree within a few degrees,

repeat the calculation using the calculated value as the new estimate. Two or three iterations are generally

sufficient to get a reasonable answer.

thermal protection

Thermal protection is provided to prevent damage to the IC when heavy-overload or short-circuit faults are

present for extended periods of time. The faults force the TPS201x into its constant current mode, which causes

the voltage across the high-side switch to increase; under short-circuit conditions, the voltage across the switch

is equal to the input voltage. The increased dissipation causes the junction temperature to rise to dangerously

high levels. The protection circuit senses the junction temperature of the switch and shuts it off. The switch

remains off until the junction has dropped approximately 20

°C. The switch continues to cycle in this manner until

the load fault or input power is removed.

ESD protection

All TPS201x terminals incorporate ESD-protection circuitry designed to withstand a 6-kV human-body-model

discharge as defined in MIL-STD-883C. Additionally, the output is protected from discharges up to 12 kV.