© 2007 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FAN2564 • Rev. 1.0.1

9

Application Information

Enable and Soft Start

A 1.4 M

Ω pull-down resistor ensures the EN pin to be in

LOW state when it is floating. The chip is in shut-down

mode when EN pin is LOW.

To enable the chip, the EN pin needs to be raised higher

than 0.95V. The output pin starts to charge up to the

final voltage. On-chip soft-start circuitry limits the peak

inrush current through VIN pin to less than the specified

load conditions.

creases, but meets the specified 100µs under the worst

Short-Circuit and Thermal Protection

The output current is short-circuit protected. When a

short-circuit fault occurs, the output current is automati-

short-circuit resistance.

Short-circuit fault or output overload may cause the die

temperature to increase and exceed maximum ratings

due to power dissipation. In such cases, depending

device may enter thermal shutdown.

When the die temperature exceeds the shutdown limit

temperature, the onboard thermal protection disables

the output until the temperature drops below its hyteresis

value, at which point the output is re-enabled and a new

soft-start sequence occurs as described above.

Thermal Considerations

For best performance, the die temperature and the

power dissipated should be kept at moderate values.

The maximum power dissipated can be evaluated based

on the following relationship:

⎭

⎬

⎫

⎩

⎨

⎧

Θ

−

=

JA

A

(max)

J

(max)

D

T

T

P

(1)

out and can be improved by providing a heat sink of sur-

rounding copper ground.

The addition of backside copper with through-holes, stiff-

eners, and other enhancements can also aid in reducing

vices located nearby must be included in design consid-

erations.

Capacitors Selection

The FAN2564 is stable with a wide range of capacitor

values and sizes.

For loop stability, a 1µF input capacitor or bigger is rec-

ommended. Tolerance, temperature, and voltage coeffi-

cients of the capacitor must be considered to ensure

effective capacitance stays around 1µF or above. There

is no special requirement on its ESR value.

An output capacitor with an effective capacitance be-

tween 1µF and 10µF is required for loop stability. The

ESR value should be within 5 to 100m

Ω. 2.2µF or 4.7µF

ceramic capacitors are recommended to ensure stability

over the full temperature, input, and output voltage

range of operation, such as those listed in Table 1.

Table 1. Recommended Capacitors

Capacitance

Size

Vendor

Part Number

1

μF

0603

MURATA

GRM188R71C105KA120

2.2

μF

0603

MURATA

GRM188R61A225KF340

2.2

μF

0402

MURATA

GRM155R60J225ME15

4.7

μF

0603

MURATA

GRM188C80G475KE19

4.7

μF

0402

MURATA

GRM155R60G475M