ML0308 Preliminary

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6/9

Rev. B, July 2005

Best results will be obtained when IPEAK is kept

below 300mA.

Capacitor Selection

Low

ESR

(Equivalent

Series

Resistance)

capacitors should be used at the output to

minimize the output ripple voltage. Multilayer

ceramic capacitors are the best choice, as they

have a very low ESR and are available in very

small packages. Their small size makes them a

good companion to the ML0308 SOT23 package.

Solid tantalum capacitors can be used, but they

will occupy more board area than a ceramic and

will have a higher ESR. Always use a capacitor

with

a

sufficient

voltage

rating.

Ceramic

capacitors also make a good choice for the input

decoupling capacitor, which should be placed as

close as possible to the ML0308. A 4.7uF input

capacitor is sufficient for most applications.

Diode Selection

For most ML0308 applications, the Motorola

MBR0520 surface mount Schottky diode (0.5A,

20V) is an ideal choice. Schottky diodes, with

their low forward voltage drop and fast switching

speed, are the best match for the ML0308. Many

different manufacturers make equivalent parts, but

make sure that the component is rated to handle at

least 0.35A.

Lowering Output Voltage Ripple

Using low ESR capacitors will help minimize the

output ripple voltage, but proper selection of the

inductor and the output capacitor also plays a big

role. The ML0308 provides energy to the load in

bursts by ramping up the inductor current, then

delivering that current to the load. If too large of

an inductor value or too small of a capacitor value

is used, the output ripple voltage will increase

because the capacitor will be slightly overcharged

each burst cycle. To reduce the output ripple,

increase the output capacitor value or add a 4.7pF

feed-forward capacitor in the feedback network of

the ML0308 (see the circuits in the Typical

Applications

section).

Adding

this

small,

inexpensive 4.7pF capacitor will greatly reduce

the output voltage ripple.