Diodes PAM2423 - Manual (Page 7)

PAM2421/PAM2422/PAM2423
Document number: DSxxxxx Rev. 1 - 1
7 of 10
www.diodes.com
November 2012
© Diodes Incorporated
PAM2421/ PAM2422/ PAM2423
A Product Line of
Diodes Incorporated
Application Information
The PAM242x are highly efficient step-up DC/DC converters that employ a current mode, 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 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:















 1
V
V
x 2 R 1 R
FB
OUT
Where V
FB
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.
Open Voltage Protection
The features internal automatic over-voltage protection, when feedback voltage is higher than 115%.
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 supply current to just 0.1µA. As with all 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 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.