TPS2047, TPS2057

TRIPLE CURRENT-LIMITED POWER-DISTRIBUTION SWITCHES

SLVS194 – APRIL 1999

17

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

GND1

IN1

EN1

EN2

OC1

OC2

OUT1

OUT2

TPS2047

GND1

IN1

EN1

EN2

OC1

OC2

OUT1

OUT2

TPS2047

Rpullup

V+

Rfilter

Rpullup

Cfilter

To USB

Controller

V+

OC3

NC

OUT3

NC

GND2

IN2

EN3

NC

GND2

IN2

EN3

NC

OC3

NC

OUT3

NC

Figure 30. Typical Circuit for OC Pin and RC Filter for Damping Inrush OC Responses

power dissipation and junction temperature

The low on-resistance on the n-channel MOSFET allows small surface-mount packages, such as SOIC, to pass

large currents. The thermal resistances of these packages are high compared to those of power packages; it

is good design practice to check power dissipation and junction temperature. The first step is to find rDS(on) at

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

temperature of interest and read rDS(on) from Figure 21. Next, calculate the power dissipation using:

P

D +

r

DS(on)

I2

Finally, calculate the junction temperature:

T

J +

P

D

RqJA ) TA

Where:

TA = Ambient Temperature °C

RθJA = Thermal resistance SOIC = 172°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.