MCP1601_13 Datasheet, PDF (12/24 Pages) Microchip Technology – 500 mA Synchronous BUCK Regulator

MCP1601
5.0 APPLICATIONS INFORMATION
Input
Voltage
2.7V-4.2V
C_IN
10 µF
MCP1601 Application Circuit
MCP1601
1 V_IN
2 SHDN
L_X 8
P_GND 7
L Range
10 µH to 22 µH
10 µH
3 FB
4 A_GND
V_OUT 6
SYNC/ ₅
PWM
C₁
47 pF
R₁
250 k
(for 1.8V)
1 M
For V_OUT < 1.2V ONLY
R₂
200 k
V_OUT Range
1.2V to 3.3V
I_OUT = 0 mA to 400 mA
C_OUT
10 µF
C_OUT Range
10 µF to 47 µF
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 R₂, 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
R1 = R2  VOUT  VFB – 1
Where: V_OUT is the desired output voltage,
V_FB is the MCP1601 internal feedback
reference voltage
R₁ is the resistor connected to V_OUT
in the voltage divider
R₂ is the resistor connected to ground
in the voltage divider
Example:
Desired V_OUT = 2.5V
V_FB = 0.8V
R₂ = 200 k
R₁ = 425 k
DS21762B-page 12
5.1.1 LEAD CAPACITOR
Capacitor C₁ is used for applications that utilize
ceramic output capacitors. To lower the PFM mode rip-
ple voltage, a 47 pf capacitor for C₁ 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), C₁ 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.
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