LT1584/LT1585/LT1587
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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.
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 example, using an LT1585CT-3.3 (TO-220, commer-
cial) and assuming:
For the Power Transistor:
VIN(Max Continuous) = 5.25V (5V + 5%), VOUT = 3.3V,
IOUT = 4.6A
TJ = 70°C + 9W (4°C/W + 1°C/W + 3°C/W) = 142°C
142°C < 150°C = TJMAX (Power Transistor Commercial
Range)
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
In both cases the junction temperature is below the maxi-
mum rating for the respective sections, ensuring reliable
operation.
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TYPICAL APPLICATIONS N
Recommended LT1587-3.45 Circuit for the Intel 486TM DX4TM Overdrive Microprocessor
PLACE AT MICROPROCESSOR SOCKET V PINS
CC
3.45V
V
IN
≥ 4.75V
IN
OUT
3A
C2
22µF
10V
C1
10µF
10V
C3 TO C6
47µF
10V
+
+
+
LT1587-3.45
C7 TO C15
0.1µF
C16 TO C24
0.01µF
GND
LT1584 • TA03
ESR OF THE 47µF IS <0.1Ω
Minimum Parts Count LT1585 Adjustable Circuit
for the Intel Pentium VRE Processor
LT1585 Transient Response
for 3.8A Load Current Step*
THERMALLOY
PLACE IN MICROPROCESSOR
7020B-MT
SOCKET CAVITY
VOUT
50mV/DIV
3.50V
4.6A
4.75V TO
5.25V
IN
OUT
LT1585CT
C1 TO C3
220µF
+
R1
110Ω
0.1%
C5 TO C10
100µF
C11 TO C20
1µF
+
10V
ADJ
IOUT
2A/DIV
16V
10V
AVX TPS
3 EACH
AVX Y5V 0805
10 EACH
AVX TPS
6 EACH
C4
330nF
16V
R2
197Ω
0.1%
1584/5/7 TA04
LT1584 • TA05
100µs/DIV
AVX CORP. (803) 448-9411
AVX X7R 0805
THERMALLOY INC. (214) 243-4321
DO NOT SUBSTITUTE COMPONENTS.
*TRANSIENT RESPONSE MEASURED WITH AN INTEL
POWER VALIDATOR. VOUT IS MEASURED AT THE
POWER VALIDATOR
486 and DX4 are trademarks of Intel Corporation.
158457a
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Linear [ Linear ]
