LT1584/LT1585/LT1587
U
W U U
APPLICATIONS INFORMATION
This is the lowest resistance path for heat flow. Proper
mounting ensures the best thermal flow from this area of
the package to the heat sink. Linear Technology strongly
recommends thermal compound at the case-to-heat sink
interface. Use a thermally conductive spacer if the case of
the device must be electrically isolated and include its
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.
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:
For example, using an LT1585CT-3.3 (TO-220, commer-
cial) and assuming:
TJ = 70°C + 9W (4°C/W + 1°C/W + 3°C/W) = 142°C
142°C < 150°C = TJMAX (Power Transistor Commercial
Range)
VIN(Max Continuous) = 5.25V (5V + 5%), VOUT = 3.3V,
IOUT = 4.6A
In both cases the junction temperature is below the maxi-
mum rating for the respective sections, ensuring reliable
operation.
TA = 70°C, θHEAT SINK = 4°C/W
θCASE-TO-HEAT SINK = 1°C/W (with Thermal Compound)
U
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
≥ 4.75V
IN
OUT
IN
3A
C2
C1
C3 TO C6
+
+
+
LT1587-3.45
C7 TO C15
0.1µF
C16 TO C24
0.01µF
22µF
10µF
47µF
10V
10V
10V
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
3.50V
4.6A
4.75V TO
5.25V
IN
OUT
LT1585CT
VOUT
50mV/DIV
C1 TO C3
220µF
+
R1
110Ω
0.1%
C5 TO C10
100µF
C11 TO C20
1µF
+
10V
ADJ
16V
10V
AVX TPS
3 EACH
IOUT
2A/DIV
AVX Y5V 0805
24 EACH
AVX TPS
4 EACH
C4
330nF
16V
R2
197Ω
0.1%
1584/5/7 TA04
LT1584 • TA05
AVX CORP. (803) 448-9411
100µs/DIV
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.
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
Linear [ Linear ]
