LT1576-5 Linear Technology, LT1576-5 Datasheet - Page 16

• Manufacturer Part Number: LT1576-5
• Description: 1.5A/ 200kHz Step-Down Switching Regulator
• Manufacturer: Linear Technology

LT1576/LT1576-5
APPLICATIONS
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
16
AND TERMINATE
TO REGULATOR
(NORMALLY EXISTS AS INTERNAL PLANE)
GROUND RING NEED NOT BE AS SHOWN
DIODE CLOSE
THEM TO THE
SAME POINT
KEEP INPUT
CAPACITOR
AND CATCH
AND BOOST NODE
OF CONNECTIONS
TO SWITCH NODE
MINIMIZE AREA
CAPACITOR DIRECTLY
U
TO HEAVY GROUND
CONNECT OUTPUT
INFORMATION
U
D1
C3
W
GND
V
L1
V
IN
IN
SW
C1
Figure 5. Suggested Layout for LT1576
Figure 6. High Speed Switching Path
C2
U
BOOST
CIRCULATING
FREQUENCY
D2
SWITCH NODE
TAKE OUTPUT DIRECTLY FROM END
OF OUTPUT CAPACITOR TO AVOID
PARASITIC RESISTANCE AND
INDUCTANCE (KELVIN CONNECTION)
HIGH
PATH
V
GND
OUT
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
SHDN/SYNC
L1
R1
FB
V
C
R2
MINIMUM SIZE
OF FEEDBACK PIN
CONNECTIONS
TO AVOID PICKUP
LOAD
C
C
1576 F06
5V
R
C
1576 F05
TERMINATE
FEEDBACK
RESISTORS AND
COMPENSATION
COMPONENTS
DIRECTLY TO
SWITCHER
GROUND PIN