MCP1612 datasheet(11/22 Pages) MICROCHIP

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DS21921B-page 11

MCP1612

5.0

APPLICATION CIRCUITS/INFORMATION

FIGURE 5-1:

Typical Application Circuit.

5.1

Typical Applications

The MCP1612 buck controller can be used in several

different applications where a voltage that is lower than

the supply voltage is required. Its small size, low cost

and high efficiency make the MCP1612 a good choice

for densely-packaged applications. The input voltage

range, low-dropout voltage and low shutdown current

make this part perfectly suited for battery-powered

applications.

5.2

Design Example

The step-by-step design of a buck converter with the

following parameters is presented to illustrate how

easy the MCP1612 is to use.

5.2.1

SETTING OUTPUT VOLTAGE

The output voltage of the MCP1612 is set by using an

external resistor-divider network. The voltage present

at FB is internally compared to a 0.8V reference

voltage. A 200 k

Ω resistor is recommended for R2, the

lower-end of the voltage divider. Using higher-value

resistors will make the circuit more susceptible to noise

on the FB pin. Lower-value resistors can be used, if

necessary.

Equation 5-1, used to calculate the output voltage, is

shown below.

EQUATION 5-1:

For this example:

The MCP1612 is capable of a 15% duty cycle.

Instability may result when the duty cycle is below 15%.

If less than 15% duty cycle operation is needed, care

must be taken to ensure stable operation.

MCP1612 3.3V to 1.2V Synchronous Buck Converter

CIN

10 µF

Ceramic

VIN

AGND

PGND

CBYP

0.1 µF

Ceramic

VCC

SHDN

3.3VIN ±10%

OFF

1000 pF

25 k

Comp

L = 3.3 µH

100 k

200 k

1.2V VOUT @ 1A

MCP1612

COUT

10 µF

Ceramic

Input voltage = 3.3V

Output voltage = 1.2V

Output current = 0A to 1A

Switching frequency = 1.4 MHz

VOUT =1.2V

VFB =0.8V

R2 =200 kΩ

R1 =100 kΩ

OUT

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

–

⎝⎠

⎛⎞

Where:

VOUT = desired output voltage

VFB = MCP1612 internal reference

voltage

R1 = top resistor value

R2 = bottom resistor value

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