MCP16301HT-ESLASHCH datasheet(18/40 Pages) MICROCHIP

18 / 40 page

MCP16301/H

DS20005004D-page 18

 2011-2015 Microchip Technology Inc.

5.4

Input Capacitor Selection

The step-down converter input capacitor must filter the

high input ripple current as a result of pulsing or

chopping the input voltage. The input voltage pin of the

MCP16301/H devices 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

multi-layer X7R dielectric is mandatory, while for

applications with limited temperature range, a

multi-layer X5R dielectric is acceptable. Typically, input

capacitance between 4.7 µF and 10 µF is sufficient for

most applications. For applications with 100 mA to

200 mA load, a 1 µF X7R capacitor can be used,

depending on the input source and its impedance.

The input capacitor voltage rating should be a minimum

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 MCP16301/H devices are internally compensated,

so the output capacitance range is limited. See

Table 5-2 for the recommended output capacitor range.

The amount and type of output capacitance and

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 MCP16301/H

devices.

The output voltage capacitor voltage rating should be a

minimum of VOUT, plus margin.

Table 5-2 contains the recommended range for the

input and output capacitor value:

5.6

Inductor Selection

The MCP16301/H devices are designed to be used

with

small

surface

mount

inductors.

Several

specifications should be considered prior to selecting

an inductor. To optimize system performance, the

inductance value is determined by the output voltage

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

constant over the output voltage range.

EQUATION 5-4:

INDUCTOR RIPPLE

CURRENT

EXAMPLE 5-3:

EQUATION 5-5:

INDUCTOR PEAK

CURRENT

An inductor saturation rating minimum of 760 mA is

recommended. Low ESR inductors result in higher

system efficiency. A trade-off between size, cost and

efficiency is made to achieve the desired results.

TABLE 5-2:

CAPACITOR VALUE RANGE

Parameter

Min

Max

CIN

2.2 µF

none

COUT

20 µF

none



------tON



VIN =12V

VOUT =3.3V

IOUT =600 mA

ILPK

I

--------

IOUT

Inductor ripple current = 319 mA

Inductor peak current = 760 mA

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