Preliminary Datasheet

LP3203

LP3203 – Ver. 1.0 Datasheet

Dec.-2006

Page 7 of 10

Applications Information

The basic LP3203 applicaton circuit is shown inTypical

Application Circuit. External component selection is

determined by the maximum load current and begins with

the selection of the inductor value and operating

frequency followed by CIN and COUT.

Inductor selection

The output inductor is selected to limit the ripple

current to some predetermined value. typically 20%~40%

of the full load current at the maximum input voltage.

Large value inductors lower ripple currents. Higher Vin or

equation. A reasonable starting point for setting ripple

The DC current rating of the inductor should be at least

equal to the maximum load current plus half the ripple

current to prevent core saturation. Thus, a 720mA rated

Inductor should be enough for most applications

(600mA+120mA). For better efficiency, choose a low

DC-resistance inductor.

trapezoidal current at the source of the top MOSFET. To

prevent large ripple voltage, a low ESR input capacitor

Sized for the maximum RMS current should be used.

RMS current is given by:

simple

worst-case

condition

is

commonly.Used for design because even significant

deviations do not offer much relief. Note that ripple

current ratings from capacitor manufacturers are often

based on only 2000 hours of life which makes it advisable

to further derate the Capacitor, or choose a capacitor

rated at a higher temperature Than required. Several

capacitors may also be paralleled to meet size or height

requirements in the design.

series resistance(ESR) that is required to minimize

voltage ripple and load step transients, an well as the

amount or bulk capacitance that is necessary to ensure

that the control loop is stable. Loop stability can be

checked by viesing the load transient response as

determined by:

Using ceramic input and output capacitors

Higher values, lower cost ceramic capacitors are now

becoming .Available in smaller case sizes ,their high

ripple current ,high voltage rating and low ESR make

them ideal for switching regulator applications. however

care must be taken when these capacitors are used at the

input and output. When a ceramic capacitor is use at

input and the power is supplied by a wall adapter through

long wires, a load step at the output can induce ringing at

large enough to damage the part.

Output voltage programming

The output voltage is set by a resistive divider according

to the

Following formula:

The external resistive divider is connected to the output,

allowing Remote voltage sensing as shown in figure3.

Efficiency considerations

The efficiency of a switching regulator is equal to the output

Power divided by the input power times 100%.it is often useful

to analyze individual losses to determine what is limiting the

efficiency and which change would produce the most

improvement efficiency can be expressed as :