Datasheet

13
LT1584/LT1585/LT1587
158457a
APPLICATIONS INFORMATION
WUU
U
TYPICAL APPLICATIONS N
U
LT1587-3.45
GND
IN
PLACE AT MICROPROCESSOR SOCKET V
CC
PINS
C1
10µF
10V
OUTV
IN
≥ 4.75V
C2
22µF
10V
C3 TO C6
47µF
10V
ESR OF THE 47µF IS <0.1Ω
LT1584 • TA03
C7 TO C15
0.1µF
C16 TO C24
0.01µF
3.45V
3A
+++
Recommended LT1587-3.45 Circuit for the Intel 486
TM
DX4
TM
Overdrive Microprocessor
LT1585 Transient Response
for 3.8A Load Current Step*
LT1584 • TA05
100µs/DIV
V
OUT
50mV/DIV
I
OUT
2A/DIV
Minimum Parts Count LT1585 Adjustable Circuit
for the Intel Pentium VRE Processor
486 and DX4 are trademarks of Intel Corporation.
*TRANSIENT RESPONSE MEASURED WITH AN INTEL
POWER VALIDATOR. V
OUT
IS MEASURED AT THE
POWER VALIDATOR
LT1585CT
ADJ
IN
AVX CORP. [phone]
THERMALLOY INC. [phone]
DO NOT SUBSTITUTE COMPONENTS.
C1 TO C3
220µF
10V
AVX TPS
3 EACH
R1
110Ω
0.1%
C4
330nF
16V
AVX X7R 0805
OUT
4.75V TO
5.25V
THERMALLOY
7020B-MT
PLACE IN MICROPROCESSOR
SOCKET CAVITY
C5 TO C10
100µF
10V
AVX TPS
6 EACH
C11 TO C20
1µF
16V
AVX Y5V 0805
10 EACH
R2
197Ω
0.1%
3.50V
4.6A
1584/5/7 TA04
+
+
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.
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