Applications Information

Enable/ Shutdown

Forcing EN (enable/ shutdown) high (>2V) enables the regulator. EN is compatible with CMOS logic gates. If

enable shutdown feature is not required, connect EN (pin 3) to IN (supply input, pin 1). See Figure 3.

Input Capacitor

A 1µF capacitor should be placed from IN to GND if there is more than 10 inches of wire between the input

and the acfilter capacitor or if a battery is used as the input .

Reference Bypass Capacitor

BYP (reference bypass) is connected to the internal voltage reference. A 470pF capacitor (C

) connected

BYP

from BYP to GND quiets this reference, providing a significant reduction in output noise. C

reduces the

BYP

regulator phase margin, when using C

, output capacitors of 2.2µF or greater are generally required to

BYP

maintain stability.

The start-up speed of 6155 is inversely proportional to the size of the reference bypass capacitor.

Applications requiring a slow ramp-up of output voltage should consider larger values of C

. Likewise, if

BYP

rapid turn-on is necessary, consider omitting C

.

BYP

If output noise is not a major concern, omit C

and leave BYP open.

BYP

Output Capacitor

An output capacitor required between OUT and GND to prevent oscillation. The minimum size of the output

capacitor is dependent upon whether a reference bypass capacitor is used. 1.0µF minimum is recommended

when C

is not used (see Figure 2). 2.2µF minimum is recommended when C

is 470pF (see Figure 1).

BYP

BYP

Larger values improve the regulator's transient response, the output capacitor value may be increased

without limit.

The output capacitor should have an ESR (effective series resistance) of about 5W or less and a resonant

frequency above 1MHz. Ultra-low-ESR capacitors can cause a low amplitude oscillation on the output and/

or underdamped transient response. Most tantalum or aluminum electrolytic capacitors are adequate; film

types will work, but more expensive. Since many aluminum electrolytics have electrolytes that freeze at

about -30°C, solid tantalums ate recommended for operation below -25°C.

At lower values for output current, less output capacitance is required for output stability. The capacitor can

be reduced to 0.47µF for current below 10mA or 0.33µF for current below 1mA.

No-Load Stability

6155 will remain stable and in regulation with no load (other than the internal voltage divider) unlike

many other voltage regulators. This is especially important in CMOS RAM keep-alive applications.

Thermal Considerations

6155 is designed to provide 150mA of continuous current in a very small package. Maximum power

dissipation can be calculated based on the output current and the voltage drop across the part. To determine

the maximum power dissipation of the package, use the junction-to-ambient thermal resistance of the device

and the following basic equation:

T

is the maximum junction temperature of the die, 125°C, and T is the ambient operating temperature.

J(max)

A

R

is layout dependent; Table 1 shows examples of junction-to-ambient thermal resistance for the 6155.

qJA

P

=

D(max)

(T

- T )

J(max)

A

JA

FC6155 150mA Low - Noise LDO Regulator