LT3085 LINER [Linear Technology], LT3085 Datasheet - Page 17

• Manufacturer Part Number: LT3085
• Description: Adjustable 500mA Single Resistor Low Dropout Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
The power in the output transistor equals:
The total power equals:
The current delivered to the SET pin is negligible and can
be ignored.
V
V
V
Power dissipation under these conditions is equal to:
Junction Temperature will be equal to:
In this case, the junction temperature is below the maximum
rating, ensuring reliable operation.
CONTROL(MAX CONTINUOUS)
IN(MAX CONTINUOUS)
OUT
P
P
P
P
P
P
Total Power Dissipation = 360mW
T
T
I
CONTROL
TOTAL
J
J
OUTPUT
DRIVE
DRIVE
OUTPUT
OUTPUT
= T
= 50°C + 360mW • 73°C/W = 76°C
= 0.9V, I
A
= P
= (V
= (3.630V – 0.9V)(8.3mA) = 23mW
+ P
= (V
= (V
= (1.575V – 0.9V)(0.5A) = 337mW
=
DRIVE
TOTAL
OUT
CONTROL
I
OUT
60
IN
IN
= 0.5A, T
– V
– V
+ P
• θ
=
= 1.575V (1.5V + 5%)
OUT
0.5A
OUT
JA
OUTPUT
60
– V
(approximated using tables)
)(I
)(I
OUT
A
= 3.630V (3.3V + 10%)
= 8.3mA
OUT
OUT
= 50°C
)(I
)
)
CONTROL
)
Reducing Power Dissipation
In some applications it may be necessary to reduce
the power dissipation in the LT3085 package without
sacrifi cing output current capability. Two techniques are
available. The fi rst technique, illustrated in Figure 8, em-
ploys a resistor in series with the regulator’s input. The
voltage drop across R
differential voltage and correspondingly decreases the
LT3085’s power dissipation.
As an example, assume: V
and I
Junction Temperature section previously discussed.
Figure 8. Reducing Power Dissipation Using a Series Resistor
OUT(MAX)
C1
= 0.5A. Use the formulas from the Calculating
V
SET
R
CONTROL
SET
S
LT3085
+
–
decreases the LT3085’s IN-to-OUT
IN
= V
CONTROL
OUT
IN
R
3085 F08
= 5V, V
S
C2
LT3085
V
V
V
IN
IN
OUT
OUT
17
= 3.3V
3085fa