LT3579IUFD-1-PBF Просмотр технического описания (PDF) - Linear Technology
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LT3579IUFD-1-PBF Datasheet PDF : 40 Pages
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LT3579/LT3579-1
APPLICATIONS INFORMATION
The following example calculates the power dissipation
in the LT3579 for a particular boost application:
(VIN = 5V, VOUT = 12V, IOUT = 1.5A, fOSC = 1MHz,
VD = 0.5V, VCESAT = 0.185V).
To calculate die junction temperature, use the appropriate
thermal resistance number and add in worst-case ambient
temperature:
TJ = TA + θJA • PTOTAL
where TJ=Die Junction Temperature, TA=Ambient
Temperature, PTOTAL is the final result from the calculations
shown in Table 4, and θJA is the thermal resistance from
the silicon junction to the ambient air.
Table 4. Boost Power Calculations Example with VIN = 5V, VOUT = 12V, IOUT = 1.5A, fOSC = 1MHz, VD = 0.5V, VCESAT = 0.185V
DEFINITION OF VARIABLES
EQUATIONS
DESIGN EXAMPLE
VALUE
DC = Switch Duty Cycle
DC = VOUT – VIN + VD
VOUT + VD – VCESAT
DC = 12V – 5V + 0.5V
12V + 0.5V – .185V
DC = 60.9%
IIN = Average Input Current
η = Power Conversion Efficiency
(typically 90% at high currents)
PSW = Switch I2R Loss
RSW = Switch Resistance (typically
45mΩ combined SW1 and SW2)
PBAC = Base Drive Loss (AC)
IIN
=
VOUT • IOUT
VIN • η
PSW = DC •IIN2 • RSW
PBAC = 13ns •IIN • VOUT • fOSC
IIN
=
12V
5V
• 1.5A
• 0.9
PSW = 0.609 • (4A)2 • 45mΩ
PBAC = 13ns • 4A • 12V • 1MHz
IIN = 4A
PSW = 438mW
PBAC = 624mW
PBDC = Base Drive Loss (DC)
PINP = Input Power Loss
PBDC
=
VIN
• IIN
40
• DC
PINP = 14mA • VIN
PBDC
=
5V
•
4A •
40
0.609
PINP = 14mA • 5V
PBDC = 305mW
PINP = 70mW
PTOTAL = 1.437W
35791f
19
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