LT1584/LT1585/LT1587
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.
For example, using an LT1585CT-3.3 (TO-220, commer-
cial) and assuming:
V
IN
(Max Continuous) = 5.25V (5V + 5%), V
OUT
= 3.3V,
I
OUT
= 4.6A
T
A
= 70°C,
θ
HEAT SINK
= 4°C/W
θ
CASE-TO-HEAT SINK
= 1°C/W (with Thermal Compound)
Power dissipation under these conditions is equal to:
P
D
= (V
IN
– V
OUT
)(I
OUT
) = (5.25 – 3.3)(4.6) = 9W
Junction temperature will be equal to:
T
J
= T
A
+ P
D
(θ
HEAT SINK
+
θ
CASE-TO-HEAT SINK
+
θ
JC
)
For the Control Section:
T
J
= 70°C + 9W (4°C/W + 1°C/W + 0.7°C/W) = 121.3°C
121.3°C < 125°C = T
JMAX
(Control Section Commercial
range)
For the Power Transistor:
T
J
= 70°C + 9W (4°C/W + 1°C/W + 3°C/W) = 142°C
142°C < 150°C = T
JMAX
(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 486
TM
DX4
TM
Overdrive Microprocessor
PLACE AT MICROPROCESSOR SOCKET V
CC
PINS
V
IN
≥
4.75V
IN
OUT
+
C1
10µF
10V
LT1587-3.45
GND
Minimum Parts Count LT1585 Adjustable Circuit
for the Intel Pentium VRE Processor
THERMALLOY
7020B-MT
4.75V TO
5.25V
IN
C1 TO C3
220µF
10V
AVX TPS
3 EACH
OUT
LT1585CT
ADJ
R1
110Ω
0.1%
R2
197Ω
0.1%
PLACE IN MICROPROCESSOR
SOCKET CAVITY
3.50V
4.6A
V
OUT
50mV/DIV
+
+
C4
330nF
16V
AVX X7R 0805
C5 TO C10
100µF
10V
AVX TPS
4 EACH
AVX CORP. (803) 448-9411
THERMALLOY INC. (214) 243-4321
DO NOT SUBSTITUTE COMPONENTS.
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.
U
W
U
U U
+
C2
22µF
10V
+
C3 TO C6
47µF
10V
C7 TO C15
0.1µF
3.45V
3A
C16 TO C24
0.01µF
LT1584 • TA03
ESR OF THE 47µF IS <0.1Ω
LT1585 Transient Response
for 3.8A Load Current Step*
C11 TO C20
1µF
16V
AVX Y5V 0805
24 EACH
1584/5/7 TA04
I
OUT
2A/DIV
100µs/DIV
LT1584 • TA05
* TRANSIENT RESPONSE MEASURED WITH AN INTEL
POWER VALIDATOR. V
OUT
IS MEASURED AT THE
POWER VALIDATOR
11
LINER [ LINEAR TECHNOLOGY ]
