MCP16331 datasheet(20/48 Pages) MICROCHIP

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MCP16331

DS20005308D-page 20

 2014-2021 Microchip Technology Inc.

5.4

Input Capacitor Selection

The step-down converter input capacitor must filter the

high input current ripple as a result of pulsing or chopping

the input voltage. The MCP16331 input voltage pin is

used to supply voltage for the power train and as a

source for internal bias. A low Equivalent Series

Resistance (ESR), preferably a ceramic capacitor, is

recommended. The necessary capacitance is dependent

upon the maximum load current and source impedance.

Three capacitor parameters to keep in mind are the

voltage rating, Equivalent Series Resistance and the

temperature rating. For wide temperature range

applications, a multilayer X7R dielectric is mandatory,

while for applications with limited temperature range, a

multilayer X5R dielectric is acceptable. Typically, input

capacitance between 4.7 µF and 20 µF is sufficient for

most applications.

The input capacitor voltage rating should be a minimum

of VIN plus margin. Table 5-2 contains the recommended

range for the input capacitor value.

5.5

Output Capacitor Selection

The output capacitor helps in providing a stable output

voltage during sudden load transients and reduces the

output voltage ripple. As with the input capacitor, X5R

and X7R ceramic capacitors are well suited for this

application.

The amount and type of output capacitance, as well as

the Equivalent Series Resistance will have a significant

effect on the output ripple voltage and system stability.

The range of the output capacitance is limited due to

the integrated compensation of the MCP16331.

The output capacitor voltage rating should be minimum

VOUT plus margin. Table 5-2 contains the recom-

mended range for the input and output capacitor value:

5.6

Inductor Selection

The MCP16331 is designed to be used with small

surface

mount

(SMT/SMD)

inductors.

Several

specifications should be considered prior to selecting

an inductor. To optimize system performance, the

inductance value is determined based on the output

voltage (Table 5-1), so the inductor current ripple is

somewhat constant over the output voltage range. The

inductor current ripple can be calculated using

Equation 5-4.

EQUATION 5-4:

INDUCTOR CURRENT

RIPPLE

EXAMPLE 5-3:

EQUATION 5-5:

INDUCTOR PEAK

CURRENT

In case of the aforementioned example, an inductor sat-

uration rating higher than 660 mA is recommended. Low

DCR inductors result in higher system efficiency. A

trade-off between size, cost and efficiency should be

made to achieve the desired results.

TABLE 5-2:

CAPACITOR VALUE RANGE

Parameter

Min.

Max.

CIN

4.7 µF

None

COUT

20 µF

—



VIN VOUT

–

----------------------------tON



VIN =12V

VOUT =3.3V

IOUT =500 mA

ILPK

I

--------

IOUT

Inductor Current Ripple = 319 mA

Peak Inductor Current = 660 mA

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