Datasheet

MCP1601
DS21762B-page 12  2003-2013 Microchip Technology Inc.
5.0 APPLICATIONS INFORMATION
FIGURE 5-1: Typical Application Circuit.
5.1 Setting Output Voltage
The MCP1601 output voltage is set by using two exter-
nal resistors for output voltages  1.2V. For output volt-
ages < 1.2V, a third 1 M series resistor is necessary
to compensate the control system. A 200 k resistor is
recommended for R
2
, the lower end of the voltage
divider. Using higher value resistors will make the cir-
cuit more susceptible to noise on the FB pin, causing
unstable operation. Lower value resistors can be used
down to 20 k or below, if necessary.
The feedback reference voltage for the MCP1601 is
typically 0.8V. The equation used to calculate the
output voltage is shown below.
EQUATION
Example:
Desired V
OUT
= 2.5V
V
FB
= 0.8V
R
2
= 200 k
R
1
= 425 k
5.1.1 LEAD CAPACITOR
Capacitor C
1
is used for applications that utilize
ceramic output capacitors. To lower the PFM mode rip-
ple voltage, a 47 pf capacitor for C
1
is used to couple
the output AC ripple voltage to the internal PFM mode
comparator. For PWM mode, only applications that use
electrolytic capacitors that have 0.2or greater of ESR
(Equivalent Series Resistance), C
1
is not necessary.
5.2 Choosing External Components
5.2.1 CAPACITORS
The MCP1601 was developed to take full advantage of
the latest ceramic capacitor technology, though electro-
lytic types can be used as well. When selecting the best
capacitor for the application, the capacitance, physical
size, ESR, temperature coefficient, ripple current rat-
ings (electrolytic) and cost are considered in making
the best choice.
When selecting ceramic capacitors for C
OUT
, the tem-
perature coefficient of the dielectric should be evalu-
ated. Two dielectrics are recommended as they are
stable over a wide temperature range (X5R and X7R).
Other dielectrics can be used, but their capacitance
should stay within the recommended range over the
entire operating temperature range.
1M
For V
OUT
< 1.2V ONLY
V
OUT
P
GND
L
X
SHDN
V
IN
1
2
3
4
8
7
6
5
MCP1601
FB
SYNC/
A
GND
Input
Voltage
2.7V-4.2V
C
IN
10 µF
10 µH
C
OUT
10 µF
R
1
250 k
(for 1.8V)
R
2
200 k
MCP1601 Application Circuit
I
OUT
= 0 mA to 400 mA
C
OUT
Range
10 µF to 47 µF
L Range
10 µH to 22 µH
C
1
47 pF
V
OUT
Range
1.2V to 3.3V
PWM
R
1
R
2
V
OUT
V
FB
1–=
Where: V
OUT
is the desired output voltage,
V
FB
is the MCP1601 internal feedback
reference voltage
R
1
is the resistor connected to V
OUT
in the voltage divider
R
2
is the resistor connected to ground
in the voltage divider