Datasheet

 2004-2013 Microchip Technology Inc. DS21921C-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resistor is recommended for R
2
, 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
C
IN
10 µF
Ceramic
V
IN
FB
A
GND
P
GND
L
x
1
10
2
C
BYP
0.1 µF
Ceramic
V
CC
SHDN
3
3.3V
IN
±10%
4
OFF
ON
1000 pF
25 k
Comp
L = 3.3 µH
100 k
200 k
1.2V V
OUT
@ 1A
5
6
7
8
MCP1612
C
OUT
10 µF
Ceramic
Input voltage = 3.3V
Output voltage = 1.2V
Output current = 0A to 1A
Switching frequency = 1.4 MHz
V
OUT
=1.2V
V
FB
=0.8V
R
2
=200k
R
1
=100k
R
1
R
2
V
OUT
V
FB
-------------
1–


=
Where:
V
OUT
= desired output voltage
V
FB
= MCP1612 internal reference
voltage
R
1
= top resistor value
R
2
= bottom resistor value