7

Application Information

The PAM242x are highly efficient step -up DC/DC

converters that employ a currentmode,fixed

f r e q u e n c y p u l s e - w i d t h m o d u l a t i o n ( P W M )

a r c h i t e c t u r e w i t h e x c e l l e n t l i n e a n d l o a d

regulation.The

operate at constant

switching frequency under medium to high load

current conditions. At light loads, these devices

operate in a pulse-skipping mode in order to

improve light-load efficiency.

The

both offer a programmable soft-

start function which minimizes inrush current

d u r i n g s t a r t u p . T h e

s o f t - s t a r t

p e r i o d

i s

programmed by connecting a 10nF capacitor

between SS and Ground. Operation of the soft-

start function is as follows: when the IC is

disabled, SS is actively discharged to Ground.

Upon enabling the IC, CSS is charged with a

4.5 A current so that the voltage at SS increases

in a controlled manner. The peak inductor current

is limited by the voltage at SS, so that the input

current is limited until the soft-start period

expires, and the regulator can achieve its full

output current rating.

The

both feature external adjustable

output voltages of up to 24V. To program the

outp ut vo ltage , sim ply con nect a resistive

voltage divider between the output, FB, and

G N D , w i t h r e s ist o r s s e t a cc o rd i n g t o t h e

following equation:

Where VFB is 1.262V.

For optimal performance, the rectifier should be

a Schottky rectifier that is rated to handle both

the output voltage as well as the peak switch

current.

The

features internal automatic over-

voltage protection, when feedback voltage is

higher than 115%.

Once the outputs achieve regulation, if the

voltage at FB falls below 0.2V the controller will

automatically disable, preventing the controller

f r o m

r u n n i n g

o p e n - l o o p

a n d

p o t e n t i a l l y

damaging the IC and load.

Drive EN low to disable the IC and reduce the

su p p ly c u rr e n t t o j u st 0 . 1 A . As w i th a l l

nonsynchronous step-up DC/DC converters, the

external Schottky diode provides a DC path from

the input to the output in shutdown. As a result,

the output drops to one diode voltage drop below

the input in shutdown.

The

both feature integrated thermal

o v e r l o a d

p r o t e c t i o n .

B o t h

d e v i c e s

a r e

a ut o ma tica lly d isab le d wh e n t he ir jun ctio n

temperatures exceed 160°C, and automatically

re-enable when the die temperature decreases

by 40°C.

PAM242x

PAM242x

PAM242x

PAM242x

PAM242x

Soft-Start

Setting the Output Voltage

Rectifier Selection

Over Voltage Protection

Open Protection

Shutdown

Thermal Shutdown

μ

μ

,

Power Analog Microelectronics Inc

www.poweranalog.com

02/2012 Rev1.1

PAM2421,PAM2422,PAM2423

3A,4.5A,5.5A PWM Step-Up DC/DC Converter