LT3480 LINER [Linear Technology], LT3480 Datasheet - Page 17

• Manufacturer Part Number: LT3480
• Description: 36V, 2A, 2.4MHz Step-Down Switching Regulator with 70?A Quiescent Current
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Figure 9. A Good PCB Layout Ensures Proper, Low EMI Operation
VIAS TO LOCAL GROUND PLANE
VIAS TO V
D1
OUT
L1
C1
VIAS TO SYNC
V
OUT
Figure 10. A Well Chosen Input Network Prevents Input Voltage Overshoot and
Ensures Reliable Operation when the LT3480 is Connected to a Live Supply
GND
24V SUPPLY
IMPEDANCE
VIAS TO RUN/SS
ENERGIZED
LOW
+
+
VIAS TO PG
+
C2
R
R
PG
RT
SIMULATES HOT PLUG
CLOSING SWITCH
AI.EI.
0.1μF
22μF
35V
STRAY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
VIAS TO V
OUTLINE OF LOCAL
GROUND PLANE
+
C
R1
C
0.7Ω
R
I
IN
C
R2
IN
V
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IN
4.7μF
4.7μF
4.7μF
LT3480
LT3480
LT3480
(10a)
(10b)
(10c)
Finally, keep the FB and V
traces will shield them from the SW and BOOST nodes.
The Exposed Pad on the bottom of the package must be
soldered to ground so that the pad acts as a heat sink. To
keep thermal resistance low, extend the ground plane as
much as possible, and add thermal vias under and near
the LT3480 to additional ground planes within the circuit
board and on the bottom side.
Hot Plugging Safely
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LT3480 circuits. However, these capaci-
tors can cause problems if the LT3480 is plugged into a
live supply (see Linear Technology Application Note 88 for
a complete discussion). The low loss ceramic capacitor,
combined with stray inductance in series with the power
20V/DIV
10A/DIV
20V/DIV
10A/DIV
20V/DIV
10A/DIV
V
V
V
I
I
I
IN
IN
IN
IN
IN
IN
DANGER
RINGING V
ABSOLUTE MAXIMUM RATING
20μs/DIV
20μs/DIV
20μs/DIV
IN
MAY EXCEED
C
nodes small so that the ground
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LT3480
17
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