lt3579iufd-trpbf Linear Technology Corporation, lt3579iufd-trpbf Datasheet - Page 19

• Manufacturer Part Number: lt3579iufd-trpbf
• Description: Lt3579/lt3579-1 6a Boost/inverting Dc/dc Converter With Fault Protection Features
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
The following example calculates the power dissipation
in the LT3579 for a particular boost application:
To calculate die junction temperature, use the appropriate
thermal resistance number and add in worst-case ambient
temperature:
Table 4. Boost Power Calculations Example with V
DC = Switch Duty Cycle
I
η = Power Conversion Effi ciency
(typically 90% at high currents)
P
R
45mΩ combined SW1 and SW2)
P
P
P
IN
SW
BAC
BDC
INP
SW
= Average Input Current
(V
V
T
DEFINITION OF VARIABLES
= Switch I
= Input Power Loss
= Switch Resistance (typically
J
D
= Base Drive Loss (AC)
= Base Drive Loss (DC)
IN
= T
= 0.5V, V
= 5V, V
A
+ θ
2
R Loss
JA
CESAT
OUT
• P
TOTAL
= 12V, I
= 0.185V).
OUT
P
BAC
DC
= 1.5A, f
P
P
=
SW
=
BDC
P
I
IN
INP
13
V
OUT
=
EQUATIONS
=
V
ns I
=
DC I
OUT
=
V
V
•
14
OUT
+
IN
V
•
OSC
IN
IN
V
IN
mA V
–
•
IN
D
•
V
•
I
40
= 5V, V
• η
2
IN
IN
–
I
V
•
OUT
•
OUT
= 1MHz,
•
V
+
R
CESAT
DC
IN
SW
V
D
•
OUT
f
OSC
= 12V, I
where T
Temperature, P
shown in Table 4, and θ
the silicon junction to the ambient air.
OUT
= 1.5A, f
P
P
BAC
SW
DC
P
=
BDC
=
J
=
DESIGN EXAMPLE
=Die Junction Temperature, T
13
P
0 609
I
INP
IN
12
OSC
.
ns
=
12
=
V
5
=
•
TOTAL
V
12
V
= 1MHz, V
+
•
14
4
5
–
•
0 5
(
A
V
V
4
mA
.
4
5
•
•
A
•
A
V
40
V
12
1 5
)
0 9
is the fi nal result from the calculations
2
•
•
+
.
– .
.
V
0 609
•
5
0 5
A
.
185
V
45
.
•
LT3579/LT3579-1
JA
1
D
V
m
MHz
V
= 0.5V, V
Ω
is the thermal resistance from
CESAT
= 0.185V
P
P
P
P
TOTAL
P
BAC
BDC
DC = 60.9%
SW
INP
I
VALUE
IN
= 438mW
= 624mW
= 305mW
= 70mW
A
= 1.437W
= 4A
=Ambient
19
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