LTC3544B

12

3544bfa

A second, more severe transient is caused by switching

in loads with large (>1μF) supply bypass capacitors. The

discharged bypass capacitors are effectively put in paral-

can deliver enough current to prevent this problem if the

load switch resistance is low and it is driven quickly. The

only solution is to limit the rise time of the switch drive

so that the load rise time is limited to approximately (25

require a 250μs rise time, limiting the charging current

to about 130mA.

PC Board Layout Checklist

When laying out the printed circuit board, the following

checklist should be used to ensure proper operation of the

LTC3544B. These items are also illustrated graphically in

Figures 3 and 4. Check the following in your layout:

1. The power traces, consisting of the PGND trace, the

trace should be kept short, direct and wide.

APPLICATIONS INFORMATION

respective feedback resistors? The resistive dividers

must be connected between the (+) plate of the cor-

responding output filter capacitor (e.g. C13) and GNDA.

If the circuit being powered is at such a distance from

the part where voltage drops along circuit traces are

large, consider a Kelvin connection from the powered

circuit back to the resistive dividers.

3. Keep C8 and C9 as close to the part as possible.

4. Keep the switching nodes (SWx) away from the sensi-

5. Keep the ground connected plates of the input and

output capacitors as close as possible.

6. Care should be taken to provide enough space between

unshielded inductors in order to minimize any trans-

former coupling.

C6

R5

R6

L2

C4

C12

R8

R11

L3

C10

C3

C1

R2

3544B F03

R3

SW200B

SW200B

SW300

SW300

PGND

SW1000

RUN100

GNDA

C15

R15

R16

RUN100

RUN200A

RUN200A

SW200A

SW200A

RUN300

RUN300

RUN200B

RUN200B

PGND

2.25V TO 5.5V

2.25V TO 5.5V

C8

L4

L1

LTC3544B

C9

C13

Figure 3. LTC3544B Layout Diagram