SC284PEVB datasheet(18/22 Pages) SEMTECH

18 / 22 page

SC284P

Applications Information (continued)

from the following equation.

Table 3 lists the manufac turers of recommended capacitor

options.

Manufacturer

Part Nunber

Value

(μF)

Type

Rated

Voltage

(VDC)

Value

3.3V

(μF)

Dimensions

LxWxH

(mm)

Murata

GRM21BR60J106K

0±0%

X5R

6.3

4.74

2.0x.25x.25

(EIA:0805)

Murata

GRM219R60J106K

0±0%

X5R

6.3

4.05

2.0x.25x0.85

(EIA:0805)

Murata

GRM21BR60J226M

22±20%

X5R

6.3

6.57

2.0x.25x.25

(EIA:0805)

Murata

GRM31CR60J476M

47±20%

X5R

6.3

20.3

3.2x.6x.6

(EIA:206)

Table 3 – Recommended Capacitors

IN Selection

The SC284P source input current is a DC supply current

with a triangular ripple imposed on it. To prevent large

input voltage ripple, a low ESR ceramic capacitor is

required. A minimum value of 0μF should be used. It is

important to consider the DC voltage coefficient charac-

teristics when determining the actual required value. It

should be noted a 0µF, 6.3V, X5R ceramic capacitor with

5V DC applied may exhibit a capacitance as low as 4.05µF.

To estimate the required input capacitor, determine the

acceptable input ripple voltage and calculate the

minimum value required for C

IN as shown by the following

equation.

The input capacitor RMS ripple current varies with the

input and output voltage. The maximum input capacitor

RMS current is found from the next equation .

The input voltage ripple and RMS current ripple are at

a maximum when the input voltage is twice the output

voltage or 50% duty cycle.

The input capacitor provides a low impedance loop for

the edges of pulsed current drawn by the PMOS switch.

Low ESR/ESL X5R ceramic capacitors are recommended

for this function. To minimize stray inductance, the capaci-

tor should be placed as close as possible to the VIN and

GND pins of the SC284P.

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