MIC2104 datasheet(30/42 Pages) MICROCHIP

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MIC2103/4

DS20005899A-page 30

 2017 Microchip Technology Inc.

subjected to high inrush currents, caused by turning the

input supply on. A tantalum input capacitor’s voltage

rating should be at least two times the maximum input

voltage to maximize reliability. Aluminum electrolytic,

OS-CON, and multilayer polymer film capacitors can

handle the higher inrush currents without voltage

de-rating.

The input voltage ripple will primarily depend on the

input capacitor’s ESR. The peak input current is equal

to the peak inductor current, so:

EQUATION 5-19:

The input capacitor must be rated for the input current

ripple. The RMS value of input capacitor current is

determined at the maximum output current. Assuming

the peak-to-peak inductor current ripple is low:

EQUATION 5-20:

The power dissipated in the input capacitor is:

EQUATION 5-21:

5.6

Voltage Setting Components

The MIC2103/4 requires two resistors to set the output

voltage as shown in Figure 5-3:

FIGURE 5-3:

Voltage-Divider

Configuration.

The output voltage is determined by the following

equation:

EQUATION 5-22:

A typical value of R1 can be between 3 kΩ and 10 kΩ.

If R1 is too large, it may allow noise to be introduced

into the voltage feedback loop. If R1 is too small in

value, it will decrease the efficiency of the buck

converter, especially at light loads. Once R1 is

selected, R2 can be calculated using Equation 5-23:

EQUATION 5-23:



LPK



ESR

CIN



CIN RMS



OUT MAX



1 D

–







DISS CIN



CIN RMS



ESR

CIN



OUT

-------







Where:

VFB = 0.8V.



OUT

–

-----------------------------

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