LT1576CS8 datasheet(16/28 Pages) LINER

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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

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

VIN

HIGH

FREQUENCY

CIRCULATING

PATH

LOAD

SWITCH NODE

Figure 5. Suggested Layout for LT1576

VOUT

VIN

BOOST

SHDN/SYNC

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

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