PAM2421 Datasheet, PDF (7/9 Pages) Power Analog Micoelectronics – 3A,4.5A,5.5A PWM Step-Up DC/DC Converter

PAM2421,PAM2422,PAM2423
3A,4.5A,5.5A PWM Step-Up DC/DC Converter
Application Information
The PAM242x are highly efficient step -up DC/DC
converters that employ a currentmode,fixed
frequency pulse-width modulation (PWM)
architecture with excellent line and load
regulation.The PAM242x 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.
Soft-Start
The PAM242x both offer a programmable soft-
start function which minimizes inrush current
during startup. The soft-start period is
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
4.5μA 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.
Setting the Output Voltage
The PAM242x both feature external adjustable
output voltages of up to 24V. To program the
output voltage, simply connect a resistive
voltage divider between the output, FB, and
GND, with resistors set according to the
following equation:
Open Protection
Once the outputs achieve regulation, if the
voltage at FB falls below 0.2V the controller will
automatically disable, preventing the controller
from running open-loop and potentially
damaging the IC and load.
Shutdown
Drive EN low to disable the IC and reduce the
su pply c urr ent to j ust 0.1μA . As wi th al 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.
Thermal Shutdown
The PAM242x both feature integrated thermal
overload protection. Both devices are
automatically disabled when their junction
temperatures exceed 160°C, and automatically
re-enable when the die temperature decreases
by 40°C.
Where VFB is 1.262V.
Rectifier Selection
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.
Over Voltage Protection
The PAM242x features internal automatic over-
voltage protection, when feedback voltage is
higher than 115%.
Power Analog Microelectronics, Inc
www.poweranalog.com
7
02/2012 Rev1.1