Ω

Ω

PC Board Layout

A properly designed PC board layout is important in

any switching regulator. The switching power stage

requires particular attention. Follow these guidelines for

good PC board layout:

1) Place decoupling capacitors as close to IC pins as

possible. Keep the power ground plane (connected

to PGND) and signal ground plane (connected to

GND) separate. Connect the two ground planes with

a single connection from PGND to GND.

2) Input and output capacitors are connected to the

power ground plane; all other capacitors are con-

nected to the signal ground plane.

3) Keep the high-current paths as short and wide as

possible.

4) If possible, connect IN, LX, and PGND separately to

a large land area to help cool the IC to further

improve efficiency and long-term reliability.

5) Ensure all feedback connections are short and

direct. Place feedback resistors (if used) as close to

the IC as possible.

6) Route high-speed switching nodes (LX) away from

sensitive analog areas (FB, COMP, SS).

R

C

C

V

I

k

C

OUT

C

OUT

OUT MAX

=×

×

=

×

×

×

×

=

−

−

05

47 10

560 10

25

05 1

41 9

6

12

.

..

.

.

()

Ω

C

V

IR

g

f

pF

C

FB

OUT MAX

CS

m

C

=

×

××

×

×

=

×

××

×

×

×

=

−

05

11

2

125

05 1

1

026

50 10

1

2

140000

547

6

.

.

..

()

π

π

Smallest 1A, 1.4MHz Step-Down Regulators

14

______________________________________________________________________________________

Chip Information

TRANSISTOR COUNT: 1998

PROCESS: BiCMOS

Ω)

2.5

4.7

4.7

560

43

1.8

4.7

4.7

560

30

Table 4. Recommended Components for the MAX1973

Ω)

1.5

4.7

4.7

330

43

1.0

4.7

4.7

330

27

Table 5. Recommended Components for the MAX1974

Selector Guide

PART

FEATURES

OUTPUT PRESET

MAX1973EUB

Voltage Margining

1.8V or 2.5V

MAX1974EUB

Power-OK Output

1V or 1.5V