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LT1584CT

7A, 4.6A, 3A Low Dropout Fast Response Positive Regulators Adjustable and Fixed

Linear Technology 

LT1584/LT1585/LT1587

APPLICATIONS INFORMATION

contribution to the total thermal resistance. Please consult

“Mounting Considerations for Power Semiconductors”

1990 Linear Applications Handbook, Volume I, Pages

RR3-1 to RR3-20. The output connects to the case of all

devices in the LT1584/LT1585/LT1587 series.

For example, using an LT1585CT-3.3 (TO-220, commer-

cial) and assuming:

VIN(Max Continuous) = 5.25V (5V + 5%), VOUT = 3.3V,

IOUT = 4.6A

TA = 70°C, θHEAT SINK = 4°C/W

θCASE-TO-HEAT SINK = 1°C/W (with Thermal Compound)

Power dissipation under these conditions is equal to:

PD = (VIN – VOUT)(IOUT) = (5.25 – 3.3)(4.6) = 9W

Junction temperature will be equal to:

TJ = TA + PD(θHEAT SINK + θCASE-TO-HEAT SINK + θJC)

For the Control Section:

TJ = 70°C + 9W (4°C/W + 1°C/W + 0.7°C/W) = 121.3°C

121.3°C < 125°C = TJMAX (Control Section Commercial

range)

For the Power Transistor:

TJ = 70°C + 9W (4°C/W + 1°C/W + 3°C/W) = 142°C

142°C < 150°C = TJMAX (Power Transistor Commercial

Range)

In both cases the junction temperature is below the maxi-

mum rating for the respective sections, ensuring reliable

operation.

TYPICAL APPLICATIONS N

Recommended LT1587-3.45 Circuit for the Intel 486TM DX4TM Overdrive Microprocessor

VIN ≥ 4.75V

+

IN

OUT

C1 LT1587-3.45 +

10µF

10V

GND

C2

22µF

10V

PLACE AT MICROPROCESSOR SOCKET VCC PINS

+ C3 TO C6

47µF

10V

C7 TO C15

0.1µF

3.45V

3A

C16 TO C24

0.01µF

ESR OF THE 47µF IS <0.1Ω

LT1584 • TA03

Minimum Parts Count LT1585 Adjustable Circuit

for the Intel Pentium VRE Processor

THERMALLOY

7020B-MT

4.75V TO

5.25V

C1 TO C3

+

220µF

IN

OUT

LT1585CT

10V

AVX TPS

ADJ

3 EACH

C4

330nF

16V

AVX X7R 0805

R1

110Ω

0.1%

R2

197Ω

0.1%

PLACE IN MICROPROCESSOR

SOCKET CAVITY

+ C5 TO C10

100µF

10V

AVX TPS

6 EACH

3.50V

4.6A

C11 TO C20

1µF

16V

AVX Y5V 0805

10 EACH

1584/5/7 TA04

AVX CORP. (803) 448-9411

THERMALLOY INC. (214) 243-4321

DO NOT SUBSTITUTE COMPONENTS.

486 and DX4 are trademarks of Intel Corporation.

LT1585 Transient Response

for 3.8A Load Current Step*

VOUT

50mV/DIV

IOUT

2A/DIV

100µs/DIV

LT1584 • TA05

*TRANSIENT RESPONSE MEASURED WITH AN INTEL

POWER VALIDATOR. VOUT IS MEASURED AT THE

POWER VALIDATOR

158457a

13

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