Datasheet

LT3980
18
3980fa
For more information www.linear.com/LT3980
High Temperature Considerations
The PCB must provide heat sinking to keep the LT3980
cool. The Exposed Pad on the bottom of the package must
be soldered to a ground plane. This ground should be
tied to large copper layers below with thermal vias; these
layers will spread the heat dissipated by the LT3980. Place
additional vias can reduce thermal resistance further. With
these steps, the thermal resistance from die (or junction)
to ambient can be reduced to
JA
= 35°C/W or less. With
100 LFPM airflow, this resistance can fall by another 25%.
Further increases in airflow will lead to lower thermal re
-
sistance. Because of the large output current capability of
the LT3980, it is possible to dissipate enough heat to raise
the junction temperature beyond the absolute maximum of
125°C. When operating at high ambient temperatures, the
maximum load current should be derated as the ambient
temperature approaches 125°C.
Power dissipation within the LT3980 can be estimated by
calculating the total power loss from an efficiency mea
-
surement and subtracting the catch diode loss and inductor
loss. The die temperature is calculated by multiplying the
LT3980 power dissipation by the thermal resistance from
junction to ambient.
Other Linear Technology Publications
Application Notes 19, 35 and 44 contain more detailed
descriptions and design information for buck regulators
and other switching regulators. The LT1376 data sheet
has a more extensive discussion of output ripple, loop
compensation and stability testing. Design Note 100
shows how to generate a bipolar output supply using a
buck regulator.
applicaTions inFormaTion
Figure 10. A Well Chosen Input Network Prevents Input Voltage Overshoot and
Ensures Reliable Operation When the LT3980 Is Connected to a Live Supply
+
LT3980
4.7µF
V
IN
20V/DIV
I
IN
10A/DIV
20µs/DIV
V
IN
CLOSING SWITCH
SIMULATES HOT PLUG
I
IN
(10a)
(10b)
LOW
IMPEDANCE
ENERGIZED
24V SUPPLY
STRAY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
+
LT3980
4.7µF0.1µF
0.7Ω
V
IN
20V/DIV
I
IN
10A/DIV
20µs/DIV
DANGER
RINGING V
IN
MAY EXCEED
ABSOLUTE MAXIMUM RATING
(10c)
+
LT3980
4.7µF
22µF
AI.EI.
3980 F10
V
IN
20V/DIV
I
IN
10A/DIV
20µs/DIV
+
Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.