LT3992EFE View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LT3992EFE' PDF : 36 Pages View PDF
LT3992
Applications Information
3992 F19
Figure 19. PCB Top Layer and Component Placement for TSSOP and QFN Packages
The LT3992’s powerful 4.6A switches allow the converter
to source large output currents. Depending on the con-
verter’s operating conditions, the resulting internal power
dissipation can raise the junction temperature beyond
its maximum rating. Operating conditions include input
voltages, output voltages, switching frequencies, output
currents, and the ambient environmental temperature,
etc. An estimation of the junction temperature rise above
ambient temperature helps determine whether a given
design may exceed the maximum junction ratings for
specific operating conditions. However, temperature rise
depends on PCB design and the proximity to other heat
sources. The final converter design must be evaluated
on the bench.
An estimation of the junction temperature rise begins by
determining which circuit components dissipate power.
In order to simplify the power loss estimation, only the
inductors, catch diodes, and the LT3992 will be considered
as heat sources. After the operating conditions have been
determined, the individual power losses are calculated by:
PowerD1,2
=
⎛
⎝⎜
1−
VOUT
VIN
⎞
⎠⎟
•IOUT
•
VFD
PowerIND1,2 = RIND •IOUT 2
PowerCH1,2
=
0.1•
VOUT
VIN
•IOUT
•VIN
+
IOUT
•
VOUT • VBOOST
40• VIN
+
2 + 2•10–3
VIN
•IOUT
•
fSW
•
10−6
•
⎛
⎝⎜
VIN
2.5
+
IOUT
0.25
⎞
⎠⎟
where:
fSW = Switching Frequency in kHz
RIND =Inductor Resis tance
VFD = Catch Diode Forward Voltage Drop
VBOOST = Switch Boost Voltage
3992fa
26
For more information www.linear.com/LT3992
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