LT3080EDD LINER [Linear Technology], LT3080EDD Datasheet - Page 14

• Manufacturer Part Number: LT3080EDD
• Description: Adjustable1.1A Single Resistor Low Dropout Regulator
• Manufacturer: LINER [Linear Technology]

LT3080
The power in the drive circuit equals:
where I
of output current. A curve of I
in the Typical Performance Characteristics curves.
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:
APPLICATIONS INFORMATION
14
Figure 8. Reducing Power Dissipation Using a Series Resistor
CONTROL(MAX CONTINUOUS)
IN(MAX CONTINUOUS)
OUT
P
P
P
PDRIVE = (V
P
P
P
Total Power Dissipation = 721mW
I
CONTROL
TOTAL
DRIVE
OUTPUT
DRIVE
OUTPUT
OUTPUT
= 0.9V, I
CONTROL
= (V
= P
= (3.630V – 0.9V)(17mA) = 46mW
= (V
= (V
= (1.575V – 0.9V)(1A) = 675mW
=
DRIVE
OUT
C1
CONTROL
I
OUT
CONTROL
60
IN
IN
is equal to I
= 1A, T
– V
– V
+ P
=
V
SET
R
= 1.575V (1.5V + 5%)
CONTROL
SET
OUT
1
60
OUT
OUTPUT
LT3080
A
– V
+
–
– V
A
=
)(I
)(I
OUT
= 50°C
17
OUT
= 3.630V (3.3V + 10%)
OUT
OUT
OUT
CONTROL
mA
)(I
/60. I
)
)(I
)
CONTROL
CONTROL
OUT
IN
CONTROL
vs I
R
3080 F08
OUT
)
S
C2
)
can be found
V
V
V
is a function
IN
IN
OUT
ʹ
Junction Temperature will be equal to:
In this case, the junction temperature is below the maxi-
mum rating, ensuring reliable operation.
Reducing Power Dissipation
In some applications it may be necessary to reduce
the power dissipation in the LT3080 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
LT3080’s power dissipation.
As an example, assume: V
and I
Junction Temperature section previously discussed.
Without series resistor R
equals:
If the voltage differential (V
transistor is chosen as 0.5V, then R
Power dissipation in the LT3080 now equals:
The LT3080’s power dissipation is now only 30% compared
to no series resistor. R
appropriate wattage resistors to handle and dissipate the
power properly.
T
T
P
R
P
J
J
TOTAL
TOTAL
S
OUT(MAX)
= T
= 50°C + 721mW • 64°C/W = 96°C
=
5V – 3.3V −0.5V
A
=1.73W
+ P
= 5V – 3.3V
= 5V – 3.3V
(
(
TOTAL
= 1A. Use the formulas from the Calculating
1A
• θ
S
S
JA
decreases the LT3080’s IN-to-OUT
)
)
dissipates 1.2W of power. Choose
S
•
•
(approximated using tables)
, power dissipation in the LT3080
IN
=1.2Ω
1A
60
1A
60
= V
DIFF
CONTROL
+ 5V – 3.3V
+ 0.5V
) across the NPN pass
(
(
S
equals:
)
= 5V, V
• 1A = 0.53W
)
• 1A
OUT
= 3.3V
3080fb