LT1934 LINER [Linear Technology], LT1934 Datasheet - Page 12

• Manufacturer Part Number: LT1934
• Description: Micropower Step-Down Switching Regulators in ThinSOT
• Manufacturer: LINER [Linear Technology]

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
APPLICATIO S I FOR ATIO
LT1934/LT1934-1
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
12
U
U
SHUTDOWN
V
IN
I
C1
Figure 6. A Good PCB Layout Ensures Proper, Low EMI Operation
GND
V
IN
SW
W
(5a)
VIAS TO LOCAL GROUND PLANE
OUTLINE OF LOCAL GROUND PLANE
C2
U
V
IN
GND
SW
(5c)
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
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.
D1
L1
V
IN
1934 F06
GND
C1
1934 F05
V
SW
SW
(5b)
V
SYSTEM
GROUND
OUT
IN
pin of the LT1934 can ring
1934f