LT1375CS8 datasheet(16/28 Pages) LINER

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LT1375/LT1376

APPLICATIONS INFORMATION

(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

including the switch, catch diode, and input capacitor is

the only one containing nanosecond rise and fall times. If

you follow this path on the PC layout, you will see that it is

irreducibly short. If you move the diode or input capacitor

away from the LT1376, get your resumé in order. The

other paths contain only some combination of DC and

500kHz triwave, so are much less critical.

Figure 5. Suggested Layout

INPUT

1375/76 F05

BOOST

BIAS

GND

SHDN

SHUTDOWN

OUTPUT

MINIMIZE AREA OF

CONNECTIONS TO THE

SWITCH NODE AND

BOOST NODE

KEEP INPUT CAPACITOR

AND CATCH DIODE CLOSE

TO REGULATOR AND

TERMINATE THEM

TO 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 SIZE OF

FEEDBACK PIN

CONNECTIONS TO

AVOID PICKUP

TERMINATE

FEEDBACK RESISTORS

AND COMPENSATION

COMPONENTS

DIRECTLY TO SWITCHER

GROUND PIN

GROUND RING NEED

NOT BE AS SHOWN.

(NORMALLY EXISTS AS

INTERNAL PLANE)

Figure 6. High Speed Switching Path

1375/76 F06

VIN

HIGH

FREQUENCY

CIRCULATING

PATH

LOAD

SWITCH NODE

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