LT1941 Просмотр технического описания (PDF) - Linear Technology
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LT1941 Datasheet PDF : 24 Pages
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APPLICATIONS INFORMATION
VIN SW
GND
VIN SW
GND
LT1941
(a)
IC1
VSW
VIN SW
C1
GND
L1
D1
(b)
C2
1941 F07
(c)
Figure 7. Subtracting the Current when the Switch is ON (a) From the Current when the Switch is OFF (b) Reveals the Path
of the High Frequency Switching Current (c) Keep This Loop Small. The Voltage on the SW and BOOST Nodes will also be
Switched; Keep these Nodes as Small as Possible. Finally, Make Sure the Circuit is Shielded with a Local Ground Plane
C9
VOUT1
GND VIN L3
CIN1
D3
C11
D1 C8
U1
L4
C12
VOUT3
D2 C10
GND
D5
C7
VOUT2
GND
PLACE VIAS UNDER GROUND PAD
TO GROUND PLANE FOR GOOD
THERMAL CONDUCTIVITY
CIN2 D4
L1
GND
1941 F08
Figure 8. Power Path Components and Topside Layout
THERMAL CONSIDERATIONS
The PCB must provide heat sinking to keep the LT1941
cool. The Exposed Pad on the bottom of the package must
be soldered to a ground plane. This ground should be tied
to other copper layers below with thermal vias; these lay-
ers will spread the heat dissipated by the LT1941. Place
additional vias near the catch diodes. Adding more copper
to the top and bottom layers and tying this copper to the
internal planes with vias can reduce thermal resistance
further. With these steps, the thermal resistance from die
(or junction) to ambient can be reduced to θJA = 25°C/W
or less. With 100 LFPM airflow, this resistance can fall
by another 25%. Further increases in airflow will lead to
lower thermal resistance.
Because of the large output current capability of the LT1941,
it is possible to dissipate enough heat to raise the junction
temperature beyond the absolute maximum of 125°C. If
two of the channels are running at full output current, the
third channel may have reduced output current capability,
limited by the maximum junction temperature. The output
1941fb
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