SC284 datasheet(16/20 Pages) SEMTECH

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SC284

Applications Information (continued)

Table 3 lists the manufacturers of recommended output

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 SC284 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 4.5µF.

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 minimise stray inductance ,the

capacitor should be placed as closely as possible to the

VIN and GND pins of the SC284.

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