PAM3116

8

www.poweranalog.com

,

Power Analog Microelectronics Inc

The PAM3116 fa mily of low-drop ou t (L DO)

regulators have several features that allow them

to apply to a wide range of applications. The

family operates with very low input voltage and

low dropout voltage (typically 300mV at full load),

making it an efficient stand-alone power supply or

post regulator for battery or switch mode power

supplies. The 1.5A output current make the

PAM3116 family suitable for powering many

m i c r o p r o c e s s o r s a n d F P G A s u p p l i e s . T h e

PAM3116 family also has low output noise

(typically 50µVRMS with 4.7µF output capacitor),

making it ideal for use in telecom equipment.

A 4.7µF or larger ceramic input bypass capacitor,

connected between V

and GND and located

close to the PAM3116, is required for stability. A

4.7 F minimum value capacitor from V to GND is

also required. To improve transient response,

noise rejection, and ripple rejection, an additional

1 0 µF

o r

l a r g e r ,

l o w

E S R

c a p a c i t o r

i s

recommended at the output. A higher-value, low

ESR output capacitor may be necessary if large,

fast-rise-time load transients are anticipated and

the device is located several inches from the

power source, especially if the minimum input

voltage of 2.5 V is used.

The PAM3116 features internal current limiting,

thermal protection and short circuit protection.

During normal operation, the PAM3116 limits

output current to about 2.5A. When current

limiting engages, the output voltage scales back

linearly until the over current condition ends.

While current limiting is designed to pr event

gross device failure, care should be taken not to

exceed the power dissipation ratings of the

pa ckag e. If th e tem perat ure of th e device

exceeds 150°C, thermal-protection circuitry will

shut down. Once the device has cooled down to

approximately 40°C below the high temp trip

point, regulator operation resumes. The short

circuit current of the PAM3116 is about 0.7A when

its output pin is shorted to ground.

The amount of heat that an LDO linear regulator

generates is:

P =(V -V )I .

All integrated circuits have a maximum allowable

junction temperature (T

max) above which

normal operation is not assured. A system

designer must design the operating environment

so that the operating junction temperature (T )

d o e s

n o t

e x c e e d t h e

m a x i m u m j u n c t i o n

t e m p e r a t u r e

( T

m a x ) .

T h e

t w o

m a i n

environmental variables that a designer can use

to improve thermal performance are air flow and

e x t e r n a l h e a t s i n k s . T h e p u r p o s e

o f t h i s

information is to aid the designer in determining

the proper operating environment for a linear

regulator that is operating at a specific power

level.

I n g e n e r a l , t h e m a x im u m e x p e c t e d p o w e r

(P (max)) consumed by a linear regulator is

computed as:

Where:

V

is the average input voltage.

V

is the average output voltage.

I

is the average output current.

I

is the quiescent current.

For most LDO regulators, the quiescent current is

insignificant compared to the average output

current; therefore, the term V

xI

can be

neglected. The operating junction temperature is

computed by adding the ambient temperature (T )

and the increase in temperature due to the

regulator' s power dissipation. The temperature

rise is computed by multiplying the maximum

expected power dissipation by the sum of the

thermal resistances between the junction and the

case R

), the case to heatsink (R

), and the

heatsink to ambient (R

). Thermal resistances

are measures of how effectively an object

dissipates heat. Typically, the larger the device,

the more surface area available for power

dissipation so that the object’

s thermal resistance

will be lower.

External Capacitor Requirements

Regulator Protection

Thermal Information

IN

O

D

IN

O

O

J

J

J

D

I (avg)

O(avg)

O(avg)

(Q)

I(avg)

(Q)

A

JC

CS

SA

μ

(

l

l

l

l

θ

θ

θ

Application Information

( )

( )

(

DMAX

I avg

O avg

O avg

I avg

Q

P

= V

-V

×I

+V

×I

1.5A Low Dropout Voltage CMOS Regulator

10/2011 Rev1.0