US1261CM Ver la hoja de datos (PDF) - Unisem

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componentes Descripción

Fabricante

US1261CM

DUAL 6A AND 1A LOW DROPOUT POSITIVE FIXED OUTPUT REGULATOR

Unisem 

US1261

select a heat sink that results in lower temperature rise Layout Consideration

than the one calculated in previous step. The following

heat sinks from AAVID and Thermaloy meet this crite- The US1261 like all other high speed linear regulators need

ria.

to be properly laid out to insure stable operation. The most

Air Flow (LFM)

important component is the output capacitor, which

Thermalloy

AAVID

0

100

200

300 400 needs to be placed close to the output pin and con-

7021B 7020B 6021PB 7173D 7141D nected to this pin using a plane connection with a

593101B 551002B 534202B 577102B 576802B low inductance path.

Note : For further information regarding the above com-

panies and their latest product offering and application

support contact your local representative or the num-

bers listed below:

Thermalloy

AAVID

PH# (214) 243-4321

PH# (603) 528-3400

Example # 2 :

Assuming the following specifications :

VIN = 3.3V

VOUT 2 = 1.5 V

VOUT 1 = 2.5 V

IOUT 2 MAX = 1.5A

IOUT 1 MAX = 0.2 A

TA = 35° C

The steps for selecting a proper heat sink to keep the

junction temperature below 135°C is given as :

1) Calculate the maximum power dissipation using :

( ) ( ) PD = IOUT1 × VIN − VOUT1 + IOUT2 × VIN − VOUT2

PD = 0.2 × (3.3 − 2.5) + 1.5 × (3.3 − 1.5) = 2.86 W

2) Assuming a TO-263 surface mount package, the junc-

tion to ambient thermal resistance of the package is:

θJA = 30° C / W for 1" square pad area

3) The maximum junction temperature of the device is cal-

culated using the equation below :

TJ = TA + PD × θJA

TJ = 35 + 2.86 × 30 = 121 ° C

Since this is lower than our selected 135°C maximum junc-

tion temperature (150°C is the thermal shutdown of the

device), TO-263 package is a suitable package for our ap-

plication.

Rev. 1.7

3/22/99

3-5

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