LTC1438CG-ADJ View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC1438CG-ADJ

Dual High Efficiency, Low Noise, Synchronous Step-Down Switching Regulators

Linear Technology 

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LTC1438/LTC1439

APPLICATIONS INFORMATION

CLP

RLP

0.01µF

10k

CSS

0.1µF

1000pF

CC1B

220pF

CC1A

1000pF

RC1

10k

COSC

CC2B

470pF

CC2A

RC2

1000pF

10k

R1

R2

OUTPUT DIVIDER

REQUIRED WITH

VPROG OPEN

220pF

10Ω

1

36

RUN/SS1 PLL LPF

1000pF

2 SENSE+ 1

35

PLLIN

3 SENSE– 1 BOOST 1 34

4

INTVCC

VPROG1

33

TGL1

5

ITH1

VIN

100k 6

POR2

32

SW1

31

TGS1

7

LTC1439

30

COSC

VIN

8

SGND

29

BG1

9

LBI

10

LBO

28

INTVCC

27

PGND

INTVCC 11 SFB1

26

BG2

100pF

22pF

1000pF

12

ITH2

13

VPROG2

14

VOSENSE2

15 SENSE– 2

25

EXTVCC

24

TGS2

23

SW2

22

TGL2

16 SENSE+ 2 BOOST 2 21

17

20

RUN/SS2 AUXON

10Ω

CSS

0.1µF

18

AUXDR

19

AUXFB

EXT

CLOCK

CB1

0.1µF

M3

DB1

+ 4.7µF

DB2

M6

CB2

0.1µF

M1 + CIN1

L1

RSENSE1

M2

D1

+

COUT1

GROUND PLANE

M5

D2

+ COUT2

L2

RSENSE2

+

M4

CIN2

++

VOUT1

VIN

–

–

–

VOUT2

+

NOT ALL PINS CONNECTED FOR CLARITY

BOLD LINES INDICATE HIGH CURRENT PATHS

1438 F13

Figure 13. LTC1439 Physical Layout Diagram

PC Board Layout Checklist

When laying out the printed circuit board, the following

checklist should be used to ensure proper operation of the

LTC1438/LTC1439. These items are also illustrated graphi-

cally in the layout diagram of Figure 13. Check the follow-

ing in your layout:

1. Are the high current power ground current paths using

or running through any part of signal ground? The

LTC1438/LTC1438X/LTC1439 ICs have their sensitive

pins on one side of the package. These pins include the

signal ground for the reference, the oscillator input, the

voltage and current sensing for both controllers and the

low-battery/comparator input. The signal ground area

used on this side of the IC must return to the bottom

plates of all of the output capacitors. The high current

power loops formed by the input capacitors and the

ground returns to the sources of the bottom N-channel

MOSFETs, anodes of the Schottky diodes and (–) plates

of CIN, should be as short as possible and tied through

a low resistance path to the bottom plates of the output

capacitors for the ground return.

2. Do the LTC1438/LTC1439 SENSE– 1 and VOSENSE2 pins

connect to the (+) plates of COUT? In adjustable applica-

tions, the resistive divider R1/R2 must be connected

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

HF decoupling capacitor should be as close as possible

to the LTC1438/LTC1439.

14389fb

23

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