Datasheet

LT1934/LT1934-1
13
1934fe
APPLICATIONS INFORMATION
and ground traces will shield it from the SW and BOOST
nodes. Figure 6 shows component placement with trace,
ground plane and via locations. Include two vias near
the GND pin of the LT1934 to help remove heat from the
LT1934 to the ground plane.
Hot Plugging Safely
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LT1934 and LT1934-1 circuits. How-
ever, these capacitors can cause problems if the LT1934
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 source forms an under damped tank
circuit, and the voltage at the V
IN
pin of the LT1934 can
ring to twice the nominal input voltage, possibly exceeding
the LT1934’s rating and damaging the part. If the input
supply is poorly controlled or the user will be plugging
the LT1934 into an energized supply, the input network
should be designed to prevent this overshoot.
Figure 6. A Good PCB Layout Ensures Proper, Low EMI Operation
SHUTDOWN
VIAS TO LOCAL GROUND PLANE
OUTLINE OF LOCAL GROUND PLANE
V
IN
V
OUT
1934 F06
SYSTEM
GROUND
Figure 5. 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
V
IN
SW
GND
(5a)
V
IN
V
SW
C2 D1 C1
1934 F05
L1
SW
GND
(5c)
V
IN
SW
GND
(5b)
I
C1