TPS2070DAP datasheet(22/29 Pages) TI

22 / 29 page

TPS2070, TPS2071

FOUR-PORT USB HUB POWER CONTROLLERS

SLVS287A – SEPTEMBER 2000 – REVISED FEBRUARY 2001

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

power dissipation and junction temperature

The major source of power dissipation for the TPS2070 and TPS2071 comes from the internal voltage regulator

and the N-channel MOSFETs. Checking the power dissipation and junction temperature is always a good

design practice. Begin by determining the rDS(on) of the N-channel MOSFET according to the input voltage and

operating temperature. As an initial estimate, use the highest operating ambient temperature of interest and

read rDS(on) from the graphs shown under the typical characteristics section of this data sheet. Using this value,

the power dissipation per switch can be calculated by:

D + rDS(on)

Multiply this number by four to get the total power dissipation coming from the N-channel MOSFETs.

The power dissipation for the internal voltage regulator is calculated using:

D + V

I(BP)

–V

O(min)

O(OUT)

The total power dissipation for the device becomes:

D(total) + P

D(voltage regulator) )

D(switch)

Finally, calculate the junction temperature:

J + PD

RqJA ) TA

Where:

TA = ambient temperature °C

RθJA = Thermal resistance °C/W, equal to inverting of derating factor found on the power dissipation

table in this data sheet.

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.

TPS2070DAP датащи(PDF) 22 Page - Texas Instruments