Datasheet

16
LT1576/LT1576-5
SWITCH NODE CONSIDERATIONS
For maximum efficiency, switch rise and fall times are
made as short as possible. To prevent radiation and high
frequency resonance problems, proper layout of the com-
ponents connected to the switch node is essential. B field
(magnetic) radiation is minimized by keeping catch diode,
switch pin, and input bypass capacitor leads as short as
possible. E field radiation is kept low by minimizing the
length and area of all traces connected to the switch pin
and BOOST pin. A ground plane should always be used
APPLICATIONS INFORMATION
WUU
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under the switcher circuitry to prevent interplane cou-
pling. A suggested layout for the critical components is
shown in Figure 5. Note that the feedback resistors and
compensation components are kept as far as possible
from the switch node. Also note that the high current
ground path of the catch diode and input capacitor are kept
very short and separate from the analog ground line.
The high speed switching current path is shown schemati-
cally in Figure 6. Minimum lead length in this path is
essential to ensure clean switching and low EMI. The path
Figure 6. High Speed Switching Path
1576 F06
5V
L1
V
IN
HIGH
FREQUENCY
CIRCULATING
PATH
LOAD
SWITCH NODE
Figure 5. Suggested Layout for LT1576
V
OUT
V
IN
SW
BOOST
SHDN/SYNC
FB
V
C
GND
1576 F05
GND
KEEP INPUT
CAPACITOR
AND CATCH
DIODE CLOSE
TO REGULATOR
AND TERMINATE
THEM TO THE
SAME POINT
CONNECT OUTPUT
CAPACITOR DIRECTLY
TO HEAVY GROUND
TAKE OUTPUT DIRECTLY FROM END
OF OUTPUT CAPACITOR TO AVOID
PARASITIC RESISTANCE AND
INDUCTANCE (KELVIN CONNECTION)
MINIMIZE AREA
OF CONNECTIONS
TO SWITCH NODE
AND BOOST NODE
GROUND RING NEED NOT BE AS SHOWN
(NORMALLY EXISTS AS INTERNAL PLANE)
MINIMUM SIZE
OF FEEDBACK PIN
CONNECTIONS
TO AVOID PICKUP
TERMINATE
FEEDBACK
RESISTORS AND
COMPENSATION
COMPONENTS
DIRECTLY TO
SWITCHER
GROUND PIN
C
C
R
C
R1
D1
C3
R2
D2
L1
C1
C2