LTC1159CS datasheet(14/20 Pages) LINER

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LTC1159/LTC1159-3.3/LTC1159-5

APPLICATIO S I FOR ATIO

Board Layout Checklist

When laying out the printed circuit board, the following

checklist should be used to ensure proper operation of the

LTC1159. These items are also illustrated graphically in

the layout diagram of Figure 8. Check the following in your

layout:

1) Are the signal and power grounds segregated? The

LTC1159 signal ground must connect separately to the

(–) plate of COUT. The other ground pin(s) should return

to the source of the N-channel MOSFET, anode of the

Schottky diode, and (–) plate of CIN, which should have

as short lead lengths as possible.

2) Does the LTC1159 Sense– pin connect to a point close

to RSENSE and the (+) plate of COUT? In adjustable

applications, the resistive divider R1, R2 must be con-

nected between the (+) plate of COUT and signal ground.

3) Are the Sense – and Sense + leads routed together with

minimum PC trace spacing? The differential decoupling

capacitor between the two Sense pins should be as

close as possible to the LTC1159. Up to 100

Ω may be

placed in series with each sense lead to help decouple

the Sense pins. However, when these resistors are

used, the capacitor should be no larger than 1000pF.

4) Does the (+) plate of CIN connect to the source of the

P-channel MOSFET as closely as possible? An addi-

tional 0.1

µF ceramic capacitor between VIN and power

ground may be required in some applications.

5) Is the VCC decoupling capacitor connected closely be-

tween the VCC pins of the LTC1159 and power ground?

This capacitor carries the MOSFET driver peak currents.

6) In adjustable versions, the feedback pin is very sensitive

to pickup from the switch node. Care must be taken to

isolate VFB from possible capacitive coupling of the

inductor switch signal.

7) Is the SHDN1 pin actively pulled to ground during

normal operation? SHDN1 is a high impedance pin and

must not be allowed to float.

P-GATE

VIN

VCC

P-DRIVE

VCC

ITH

SENSE–

CAP

SHDN2

EXTVCC

N-GATE

P-GND

S-GND

SENSE+

COUT

P-CHANNEL

3300pF

RSENSE

N-CHANNEL

CIN

–

VOUT

VIN

OUTPUT DIVIDER

REQUIRED WITH

ADJUSTABLE

VERSION ONLY

BOLD LINES INDICATE HIGH CURRENT PATHS

LTC1159 • F08

1000pF

100pF

µF

0.15

µF

1N4148

SHUTDOWN

5V EXTVCC

CONNECTION

0.1

µF

VFB

(SHDN1)

Figure 8. LTC1159 Layout Diagram (N and S Packages)

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