LT3513 LINER [Linear Technology], LT3513 Datasheet - Page 18

• Manufacturer Part Number: LT3513
• Description: 2MHz High Current 5-Output Regulator for TFT-LCD Panels
• Manufacturer: LINER [Linear Technology]

LT3513
Printed Circuit Board Layout
For proper operation and minimum EMI, care must be
taken during printed circuit board (PCB) layout. Figure 3
shows the high current paths in the step-down regula-
tor circuit. Note that in the step-down regulators, large,
switched currents fl ow in the power switch, the catch
diode and the input capacitor. In the step-up regulators,
large, switched currents fl ow through the power switch,
the switching diode and the output capacitor. In SEPIC and
inverting regulators, the switched currents fl ow through
the power switch, the switching diode and the tank capaci-
tor. The loop formed by the components in the switched
current path should be as small as possible. Place these
components, along with the inductor and output capacitor,
on the same side of the circuit board, and connect them
on that layer. Place a local, unbroken ground plane below
these components, and tie this ground plane to system
ground at one location, ideally at the ground terminal of
OPERATION
18
Figure 3. Subtracting the Current When the Switch is On (3a)
from the Current When the Switch is Off (3b) Reveals the Path of
the High Frequency Switching Current (3c) 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
I
C1
C1
V
V
V
IN
IN
IN
GND
GND
GND
SW
SW
SW
(3a)
(3b)
(3c)
V
SW
D1
L1
3519 F03
C2
the output capacitor C2. Additionally, keep the SW and
BOOST nodes as small as possible.
Thermal Considerations
The PCB must provide heat sinking to keep the LT3513
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 LT3513. 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 θ
or less. With 100LFPM airfl ow, this resistance can fall
by another 25%. Further increases in airfl ow will lead to
lower thermal resistance.
Figure 4. Topside PCB Layout
JA
= 25°C
3513fa