lt1941 Linear Technology Corporation, lt1941 Datasheet - Page 19

• Manufacturer Part Number: lt1941
• Description: Triple Monolithic Switching Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
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
layers 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
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
U
V
IN
GND
U
SW
I
C1
(a)
PLACE VIAS UNDER GROUND PAD
V
TO GROUND PLANE FOR GOOD
OUT1
THERMAL CONDUCTIVITY
W
Figure 8. Power Path Components and Topside Layout
C9
D1 C8
C1
U
D3
GND
V
IN
GND
C
IN1
V
GND
U1
SW
IN
(c)
V
C11
SW
L3
(or junction) to ambient can be reduced to θ
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
C
IN2
D1
D5
D4
L4
L1
D2
C12
C7
C10
GND
V
IN
C2
GND
1941 F07
V
V
GND
L1
OUT3
OUT2
1941 F08
SW
(b)
JA
LT1941
= 25°C/W
19
1941fa