IRU1260CM Ver la hoja de datos (PDF) - International Rectifier

Número de pieza

componentes Descripción

Fabricante

IRU1260CM

DUAL 6A AND 1A LOW DROPOUT POSITIVE ADJUSTABLE REGULATOR

International Rectifier 

IRU1260

Stability

The IRU1260 requires the use of an output capacitor as

part of the frequency compensation in order to make the

regulator stable. Typical designs for the microprocessor

applications use standard electrolytic capacitors with

typical ESR in the range of 50 to 100mΩ and the output

capacitance of 500 to 1000µF. Fortunately as the ca-

pacitance increases, the ESR decreases resulting in a

fixed RC time constant. The IRU1260 takes advantage

of this phenomena in making the overall regulator loop

stable. For most applications a minimum of 100µF alu-

minum electrolytic capacitor with the maximum ESR of

0.3Ω such as Sanyo, MVGX series, Panasonic FA se-

ries as well as the Nichicon PL series insures both sta-

bility and good transient response. The IRU1260 also

requires a 1µF ceramic capacitor connected from Vin to

Vctrl and a 10Ω, 0.1W resistor in series with Vctrl pin in

order to further insure stability.

Thermal Design

The IRU1260 incorporates an internal thermal shutdown

that protects the device when the junction temperature

exceeds the maximum allowable junction temperature.

Although this device can operate with junction tempera-

tures in the range of 150$C, it is recommended that the

selected heat sink be chosen such that during maxi-

mum continuous load operation the junction tempera-

ture is kept below this number. Two examples are given

which shows the steps in selecting the proper regulator

heat sink for driving the Pentium II processor GTL+ ter-

mination resistors and the Clock IC using the IRU1260

in TO-220 or TO-263 packages.

Example # 1:

2) Select a package from the data sheet and record its

junction to case (or Tab) thermal resistance.

Selecting TO-220 package gives us:

θJC = 2.7$C/W

3) Assuming that the heat sink is black anodized, cal-

culate the maximum heat sink temperature allowed:

Assume , θSA = 0.05$C/W (heat-sink-to-case thermal

resistance for black anodized)

TS = TJ - PD × (θJC + θCS)

TS = 135 - 10 × (2.7 + 0.05) = 107.4$C

4) With the maximum heat sink temperature calculated

in the previous step, the heat-sink-to-air thermal re-

sistance θSA is calculated as follows:

∆T = TS - TA = 107.4 - 35 = 72.4$C

θSA =

∆T

PD

=

72.4

10

= 7.24$C/W

5) Next, a heat sink with lower θSA than the one calcu-

lated in step 4 must be selected. One way to do this

is to simply look at the graphs of the “Heat Sink Temp

Rise Above the Ambient” vs. the “Power Dissipation”

and select a heat sink that results in lower tempera-

ture rise than the one calculated in previous step.

The following heat sinks from AAVID and Thermalloy

meet this criteria.

Thermalloy

AAVID

Air Flow (LFM)

0

100

200

300

400

7021B 7020B 6021PB 7173D 7141D

593101B 551002B 534202B 577102B 576802B

Assuming the following specifications:

VIN = 3.3V

VOUT2 = 1.5V

VOUT1 = 2.5V

IOUT2(MAX) = 5.4A

IOUT1(MAX) = 0.4A

TA = 35$C

The steps for selecting a proper heat sink to keep the

junction temperature below 135$C is given as:

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...........PH# (214) 243-4321

AAVID.................PH# (603) 528-3400

1) Calculate the maximum power dissipation using:

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

PD = 0.4 × (3.3 - 2.5) + 5.4 × (3.3 - 1.5) = 10W

Rev. 1.9

07/03/01

5

Share Link: