MCP1602
DS22061A-page 14 © 2007 Microchip Technology Inc.
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 kΩ.
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:
R
COMP
= 4.99 kΩ
C
COMP
= 33 pF
Refer to Figure 6-2 for proper placement of R
COMP
and
C
COMP
.
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 (V
OUT
) to
input voltage (V
IN
) relationship of V
OUT
/V
IN
. 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:
R
BOT
R
TOP
V
FB
V
OUT
V
FB
–
-----------------------------
⎝⎠
⎛⎞
×=
Example:
R
TOP
= 200 kΩ
V
OUT
=1.0V
V
FB
0.8V
R
BOT
= 200 kΩ x (0.8V/(1.0V - 0.8V))
R
BOT
= 800 kΩ
(Standard Value = 787 kΩ)
I
CIN RMS,
I
OUT MAX,
V
OUT
V
IN
V
OUT
–()×
V
IN
----------------------------------------------------- -
⎝⎠
⎜⎟
⎛⎞
×=
ΔV
OUT
ΔI
L
ESR×
ΔI
L
8 fC××
---------------------+=
