LT1576CS8-SYNC 데이터 시트보기 (PDF) - Linear Technology
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LT1576CS8-SYNC Datasheet PDF : 28 Pages
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LT1576/LT1576-5
APPLICATIONS INFORMATION
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
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
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
KEEP INPUT
CAPACITOR
AND CATCH
DIODE CLOSE
TO REGULATOR
AND TERMINATE
THEM TO THE
SAME POINT
C1
VOUT
L1
D2
C2
SW
D1
C3
VIN
BOOST
GND
GND
GROUND RING NEED NOT BE AS SHOWN
(NORMALLY EXISTS AS INTERNAL PLANE)
SHDN/SYNC
MINIMUM SIZE
OF FEEDBACK PIN
CONNECTIONS
TO AVOID PICKUP
R2
FB
R1 VC
CC
RC
Figure 5. Suggested Layout for LT1576
SWITCH NODE
L1
5V
HIGH
FREQUENCY
VIN
CIRCULATING
PATH
LOAD
16
1576 F06
Figure 6. High Speed Switching Path
TERMINATE
FEEDBACK
RESISTORS AND
COMPENSATION
COMPONENTS
DIRECTLY TO
SWITCHER
GROUND PIN
1576 F05
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