2014. 01. 04

13/15

Revision No : 0

FTD8210

Application Information

Input Capacitor Selection

drawn from the input supply and reduces noise injection into the

IC. The reflected ripple voltage will be smaller when an input

capacitor with larger capacitance is used. For reliable operation, it

is recommended to select the capacitor with maximum voltage

rating at least 1.2 times of the maximum input voltage. The

capacitors should be placed close to the VIN and the GND.

Inductor Selection

Selecting an inductor with low dc resistance reduces conduction

losses and achieves high efficiency. The efficiency is moderated

whilst using small chip inductor which operates with higher

inductor core losses. Therefore, it is necessary to take further

consideration while choosing an adequate inductor. Mainly, the

inductor value determines the inductor ripple current: larger

inductor value results in smaller inductor ripple current and lower

conduction losses of the converter. However, larger inductor value

generates slower load transient response. A reasonable design

be obtained as below,

where

η

= Efficiency

△

(0.3 to 0.5 typical)

To avoid the saturation of the inductor, the inductor should be

rated at least for the maximum input current of the converter plus

the inductor ripple current. The maximum input current is

calculated as below:

The peak inductor current is calculated as the following equation:

Output Capacitor Selection

The current-mode control scheme of the FTD8210 allows the usage

of tiny ceramic capacitors. The higher capacitor value provides

good load transients response. Ceramic capacitors with low ESR

values have the lowest output voltage ripple and are

recommended. If required,tantalum capacitors may be used as

well. The output ripple is the sum of the voltages across the ESR

and the ideal output capacitor.