For the best transient response in applications with

large step loads (see the Input and Output Capacitor

Selection section for output capacitance requirements),

use the following equations to select the compensation

components:

To use a low-cost ceramic capacitor (see the Input and

Output Capacitor Selection section for load-transient

response characteristics), use the following equations

to select the compensation components:

Example

OUTPUT 1 of Figure 1 is used in this example. Table 1

shows the values required to calculate the compensa-

tion. The values were taken from the appropriate data

sheets and Figure 1.

PC Board Layout Guidelines

Due to the high-current paths and tight output accuracy

required by most applications, careful PC board layout is

required. An evaluation kit (MAX8563EVKIT) is available

to speed design.

It is important to keep all traces as short as possible to

maximize the high-current trace dimensions to reduce the

effect of undesirable parasitic inductance. The MOSFET

dissipates a fair amount of heat due to the high currents

involved, especially during large input-to-output voltage

differences. To dissipate the heat generated by the

MOSFET, make power traces very wide with a large

amount of copper area. An efficient way to achieve good

power dissipation on a surface-mount package is to lay

out copper areas directly under the MOSFET package on

multiple layers and connect the areas through vias. Use a

ground plane to minimize impedance and inductance. In

addition to the usual high-power considerations, here are

four tips to ensure high output accuracy:

•

short and direct.

•

Place the feedback resistors next to the FB pin.

•

•

Ensure FB_ and DRV_ traces are away from noisy

sources to ensure tight accuracy.

gS x

A

A

S

Cx

Vx

F x

S x

Sx

m

Sx

V

A

pF

F use

F

C MAX

C

()

.

.

.

.

.

.

.

.

.

.

.,

.

==

=

+

⎛

⎝⎜

⎞

⎠⎟

+

()

−

=

30

15

88

12 4

016

1 5

100

12 4

12 4

18

1

12 4

1 5

1 5

2500

0 90

1

2

μ

μμ

Ω

R

Rx

Vx

F x

S x

m

FS x

V

A

use

C

.

.

.

.

.

.

,

.

=

+

()

+

()

=

59

1 5

100

12 4

18

1

1

124

15

15

599 4

620

μ

μ

Ω

ΩΩ

C

Cx g

gx V

I

C

Rx

C

Cx g

C

OUT

C MAX

C MAX

OUT

OUT MAX

ISS

C

OUT

C

C MAX

()

()

_

()

=

+

()

=

−

15

C

VC

gg

R

gV

I

C

R

Vx C

g

x R

Cx g

V

I

C

OUT

OUT

C MAX

C MAX

ESR

C MAX

OUT

OUT MAX

ISS

C

OUT

OUT

C MAX

ESR

C

C MAX

OUT

OUT

.

()

()

()

_

()

()

_

=

××

×

××

+

()

⎡

⎣

⎢

⎢

⎤

⎦

⎥

⎥

×+

()

=×

+

()

×+

−

016

1

59

1

2

MAX

MAX

()

±1%, Ultra-Low Output Voltage, Dual and Triple

Linear n-FET Controllers

12

______________________________________________________________________________________

Table 1. Parameters Required to

Calculate Compensation

PARAMETER

CONDITIONS

VALUE

UNITS

2500

pF

MOSFET GFS

IDFS = 8.8A

30

S

Figure 1

1.5

V

Figure 1

1.5

A

Figure 1

100

µF

Figure 1

18

m

Ω