Datasheet

10W, Dual Output
VER:00 Page 20 of 26 Issued Date：2009/03/02
Input Source Impedance
The converter
should be connected to a low impedance input source. Highly inductive source impedance can
affect the stability of the converter. Input external L-C filter is recommended to minimize input reflected
ripple current.
The inductor has a source impedance of 12μH and capacitor is Nippon chemi-con KY series 100
μF/100V. The
capacitor must be located as close as possible to the input terminals of the converter for lowest impedance.
Output Over Current Protection
When excessive output currents occur in the system, circuit protection is required on all converters. Normally,
overload current is maintained atapproximately 150 percent of rated current for PXF40-xxSxx series.
Hiccup-
mode is a method of operation in a converter whose purpose is to protect the power supply from being
damaged during an over-
current fault condition. It also enables the converter to restart when the fault is removed.
There are other ways of protecting theconverter when it is over-
loaded, such asthe maximum current limiting orcurrent
foldback methods.
One of the problems resulting from over current is that excessive heat may be generated in power devices;
especially MOSFET and Sc
hottky diodes and the temperature of these devices may exceed their specified limits. A
protection mechanism has to be used to prevent these powerdevices from being damaged.
The operation of hiccup is as follows.When the current sense circuit sees an over-
current event, the controller shuts
off the converter for a given time and then tries to start up the converter again. If the over-
load condition has been
removed, the converter will start up and operate normally; otherwise, the controller will see another over-
current event
and will shut off the converter again, repeating the previous cycle. Hiccup operation has none of the drawbacks of the
other two protection methods, although its circuit is more complicated because it requires a timing circuit. The ex
cess
heat due to overload lasts for only a short duration in the hiccup cycle, hence the junction temperature of the power
devices is much lower.
Output Over Voltage Protection
The output over-voltage protection consists of an output Zener diode that
monitors the voltage on the output
terminals. If the voltage on the output terminals exceeds the over-
voltage protection threshold, then the Zener diode
clamps the output voltage.
Short Circuitry Protection
Continuous, hiccup and auto-recovery mode.