lt3579iufd-trpbf Linear Technology Corporation, lt3579iufd-trpbf Datasheet - Page 17

• Manufacturer Part Number: lt3579iufd-trpbf
• Description: Lt3579/lt3579-1 6a Boost/inverting Dc/dc Converter With Fault Protection Features
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Inverting Topology Specifi c Layout Guidelines
• Keep ground return path from the cathode of D1 (to
• Keep length of loop (high speed switching path)
THERMAL CONSIDERATIONS
For the LT3579 to deliver its full output power, it is imp-
erative that a good thermal path be provided to dissipate
chip) separated from output capacitor C
return path (to chip) in order to minimize switching
noise coupling into the output. Notice the separate
ground return for D1’s cathode in Figure 11.
governing switch, fl ying capacitor C1, diode D1, and
ground return as short as possible to minimize parasitic
inductive spikes at the switch node during switching.
A– RETURN C
B– RETURN C
L1, L2 –MOST COUPLED INDUCTOR MANUFACTURERS USE CROSS PINOUT FOR IMPROVED PERFORMANCE.
IN
OUT
AND L2 GROUND DIRECTLY TO LT3579 EXPOSED PAD PIN 21. IT IS ADVISED TO NOT COMBINE C
GROUND DIRECTLY TO LT3579 EXPOSED PAD PIN 21. IT IS ADVISED TO NOT COMBINE C
Figure 10. Suggested Component Placement for SEPIC Topology in FE20 Package
–
V
+
IN
C
VIAS TO GROUND PLANE REQUIRED TO IMPROVE
THERMAL PERFORMANCE
IN
L1
OUT
A
’s ground
10
1
2
3
4
5
6
7
8
9
L2
21
the heat generated within the package. This can be
accomplished by taking advantage of the thermal pad on
the underside of the IC. It is recommended that multiple
vias in the printed circuit board be used to conduct heat
away from the IC and into a copper plane with as much
area as possible.
Power & Thermal Calculations
Power dissipation in the LT3579 chip comes from four
primary sources: switch I
(AC), NPN base drive loss (DC), and additional V
current. These formulas assume continuous mode
operation, so they should not be used for calculating
thermal losses or effi ciency in discontinuous mode or at
light load currents.
C1
GND
20
19
18
17
16
15
14
13
12
11
D1
OUT
B
GROUND WITH GND EXCEPT AT THE EXPOSED PAD.
IN
AND L2 GROUND WITH GND EXCEPT AT THE EXPOSED PAD.
3579 F10
C
OUT
LT3579/LT3579-1
SYNC
SHDN
CLKOUT
V
2
–
+
OUT
R loss, NPN base drive loss
17
IN
35791f
pin