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Fabricante

ADP1148

High Efficiency Synchronous Step-Down Switching Regulators

Analog Devices 

ADP1148, ADP1148-3.3, ADP1148-5

Board Layout

When laying out the printed circuit board, the following check

list should be used to ensure proper operation of the ADP1148.

These items are also illustrated graphically in the layout diagram

of Figure 18. Check the following in your layout:

1) Are the signal and power grounds segregated? The ADP1148

SIGNAL GND (Pin 11) must return to the (–) plate of COUT.

The power ground returns 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 ADP1148 SENSE(–), (Pin 7), connect to a point

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

versions the resistive divider R1, R2 must be connected be-

tween the (+) plate of COUT and signal ground.

3) Are the SENSE(–) and SENSE(+) leads routed together with

minimum PC trace spacing? The 1000 pF capacitor between

Pins 7 and 8 should be as close as possible to the ADP1148.

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

P-channel MOSFET as closely as possible? This capacitor

provides the ac current to the P-channel MOSFET.

5) Is the input decoupling capacitor (1 µF) connected closely

between VIN (Pin 3) and POWER GND (Pin 12)? This

capacitor carries the MOSFET driver peak currents.

6) Is INTVCC (Pin 5) decoupled with a 10 nF capacitor to

signal ground?

7) Is the SHUTDOWN (Pin 10) actively pulled to ground

during normal operation? The Shutdown pin is high imped-

ance and must not be allowed to float.

To prevent noise spikes from erroneously tripping the current

comparator, a 1000 pF capacitor is needed across Sense(–) and

Sense(+).

P-CHANNEL

D1

CIN

VIN

1

P-DRIVE

2 NC

14

N-DRIVE

NC 13

1␮F 3

ADP1148

12

VIN

POWER GND

CT

10nF

4

CT

5

3300pF

6

INT VCC

ITH

1k⍀

7

SENSE(–)

11

SIGNAL GND

10

SHUTDOWN

9

VFB

8

SENSE(+)

N-CHANNEL

R1

R2

–

L

–

COUT

VOUT

RSENSE

1000pF

NC = NO CONNECT

R1, R2 OUTPUT DIVIDER REQUIRED

FOR ADJUSTABLE VERSION ONLY.

Figure 18. ADP1148 Layout Diagram (See Board Layout)

REV. A

–11–

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