MCP1612 Microchip Technology, MCP1612 Datasheet - Page 11

• Manufacturer Part Number: MCP1612
• Description: 1.4 MHz Synchronous Buck Regulator
• Manufacturer: Microchip Technology

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5.0
FIGURE 5-1:
5.1
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
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
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
lower-end of the voltage divider. Using higher-value
© 2005 Microchip Technology Inc.
Switching frequency = 1.4 MHz
OFF
3.3V
Output voltage = 1.2V
Output current = 0A to 1A
APPLICATION CIRCUITS/INFORMATION
Typical Applications
Design Example
Input voltage = 3.3V
Ceramic
SETTING OUTPUT VOLTAGE
IN
10 µF
ON
±10%
C
IN
Typical Application Circuit.
Ceramic
0.1 µF
C
MCP1612 3.3V to 1.2V Synchronous Buck Converter
BYP
1000 pF
25 k
10
1
2
3
4
V
V
SHDN
Comp
IN
CC
2
, the
MCP1612
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.
P
A
Where:
GND
GND
FB
L
V
x
V
OUT
V
R
R
OUT
V
FB
8
7
6
5
R
R
FB
2
1
1
2
L = 3.3 µH
= 1.2V
= 0.8V
= 200 k
= 100 k
= desired output voltage
= MCP1612 internal reference
= top resistor value
= bottom resistor value
R
voltage
1
=
R
2
C
10 µF
Ceramic
⎛
⎝
V
------------- 1
OUT
V
OUT
MCP1612
1.2V V
FB
–
DS21921B-page 11
⎞
⎠
OUT
100 k
200 k
@ 1A