MCP1602 datasheet(14/26 Pages) MICROCHIP

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MCP1602

DS22061A-page 14

5.0

APPLICATION INFORMATION

5.1

Typical Applications

The MCP1602 synchronous buck regulator with power-

good operates over a wide input voltage range

(2.7V to 5.5V) and is ideal for single-cell Li-Ion battery

powered applications, USB powered applications,

three cell NiMH or NiCd applications and 3V to 5V

regulated input applications.

5.2

Fixed Output Voltage Applications

The

Typical Application Circuit shows a fixed

MCP1602 in a typical application used to convert three

NiMH batteries into a well regulated 1.5V @ 500 mA

output. A 4.7 µF input and output capacitor, a 4.7 µH

inductor, and a small RC filter make up the entire

external component selection for this application. No

external voltage divider or compensation is necessary.

In addition to the fixed 1.5V option, the MCP1602 is

also available in 1.2V, 1.8V, 2.5V, or 3.3V fixed voltage

options.

5.3

Adjustable Output Voltage

Applications

When the desired output for a particular application is

not covered by the fixed voltage options, an adjustable

MCP1602 can be used. The circuit listed in Figure 6-2

shows an adjustable MCP1602 being used to convert a

5V rail to 1.0V @ 500 mA. The output voltage is adjust-

able by using two external resistors as a voltage

divider. For adjustable output voltages, it is recom-

mended that the top resistor divider value be 200 k

Ω.

The bottom resistor value can be calculated using the

following equation.

EQUATION 5-1:

For adjustable output applications, an additional R-C

compensation network is necessary for control loop

stability. Recommended values for any output voltage

are:

RCOMP = 4.99 kΩ

CCOMP = 33 pF

Refer to Figure 6-2 for proper placement of RCOMP and

CCOMP.

5.4

Input Capacitor Selection

The input current to a buck converter, when operating

in continuous conduction mode, is a squarewave with

a duty cycle defined by the output voltage (VOUT) to

input voltage (VIN) relationship of VOUT/VIN. To prevent

undesirable input voltage transients, the input capacitor

should be a low ESR type with a RMS current rating

given by Equation 5-2. Because of their small size and

low ESR, ceramic capacitors are often used. Ceramic

material X5R or X7R are well suited since they have a

low temperature coefficient and acceptable ESR.

EQUATION 5-2:

Table 5-1 contains the recommend range for the input

capacitor value.

5.5

Output Capacitor Selection

The output capacitor helps provide a stable output

voltage during sudden load transients, smooths the

current that flows from the inductor to the load, and it

also reduces the output voltage ripple. Therefore, low

ESR capacitors are a desirable choice for the output

capacitor. As with the input capacitor, X5R and X7R

ceramic capacitors are well suited for this application.

The output ripple voltage is often a design specifica-

tion. A buck converters’ output ripple voltage is a

function of the charging and discharging of the output

capacitor and the ESR of the capacitor. This ripple

voltage can be calculated by Equation 5-3.

EQUATION 5-3:

BOT

TOP

OUT

–

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

⎝⎠

⎛⎞

Example:

RTOP

200 k

VOUT

=1.0V

VFB

0.8V

RBOT

200 k

Ω x (0.8V/(1.0V - 0.8V))

RBOT

800 k

(Standard Value = 787 k

Ω)

CIN RMS

OUT MAX

OUT

–

()

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

⎝⎠

⎜⎟

⎛⎞

ΔV

OUT

ΔI

ESR

ΔI

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

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