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 2006 Semtech Corp.

www.semtech.com

SC486

POWER MANAGEMENT

Layout Guidelines (Cont.)

The layout can be considered in three parts, the control section referenced to VSSA, the VTT output, and the

switcher power section. Looking at the control section first, locate all components referenced to VSSA1 on the

schematic and place these components at the chip. Connect VSSA using a wide (>0.020”) trace. Very little current

flows in the chip ground therefore large areas of copper are not needed. Connect the VSSA pin directly to the

thermal pad under the device as the only connection to PGND from VSSA.

VDDQ

C12

1u

5VRUN

C3

no-pop

R7 10R

REF

R6

10R

C9

1u

R4 10R

C2

1u

R5 4k64

R8

23k2

C11

1n

C1

no-pop

C10

no-pop

PGND1

18

REF

8

EN/PSV

1

TON

2

VDDQS

3

VCCA

5

FB

6

PGD

7

VSSA

4

PGND2

17

DL

19

VDDP

20

ILIM

21

LX

22

DH

23

BST

24

VTTEN

11

VTT

15

PGND2

16

VTTIN

12

VTTIN

13

VTT

14

VTTS

10

COMP

9

PAD

U1

SC486

C18

1u

Figure 7: Components Connected to VSSA

Figure 8: Example VSSA 0.020” Trace