MCP1612-I 查看數據表（PDF） - Microchip Technology
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MCP1612-I Datasheet PDF : 22 Pages
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Solving for C:
Where:
C = IC -----V--t-C--
IC = peak-to-peak ripple current
t = on-time of P-channel MOSFET
VC = output ripple voltage
There will also be some ripple voltage caused by the
ESR of the capacitor. The ripple is defined as follows.
EQUATION 5-7:
VESRRIPPLE = ESR IC
For this example:
IC = 165 mA
C = 4.7 µF
t = 260 ns
ESR = 8 m
VC = (260 ns x 165 mA)/4.7 µF
VC = 9.13 mV
VESRRIPPLE = 8 m x 165 mA
VESRRIPPLE = 1.32 mV
VOUT = VC + VESRRIPPLE
VOUT = 9.13 mV + 1.32 mV
VOUT = 10.45 mV
5.2.4 INPUT CAPACITOR
For the buck topology, the input current is pulled from
the source and the input capacitor in pulses. The size
of the input capacitor will determine the amount of
current pulled from the source. For most applications,
a 10 µF ceramic capacitor connected between the
MCP1612’s VIN and PGND is recommended to filter the
current pulses. Less capacitance can be used for
applications that have low source impedance. The
ripple current rating for ceramic capacitors are typically
very high due to their low loss characteristics. Low-cost
electrolytic capacitors can be used, but their ripple
current rating should not be exceeded.
5.2.5
VCC INPUT
The VCC input is used to bias the internal MCP1612
circuitry. A 10 resistor is recommended between the
unregulated inputs VIN and VCC, along with a 0.1 µF
capacitor to ground to help isolate the VCC pin from the
switching noise.
MCP1612
5.2.6 COMPENSATION COMPONENTS
An internal transconductance error amplifier is used to
compensate the buck converter. An external resistor
(RC) and capacitor (CC), connected between COMP
and GND, are all that is needed to provide a high-
bandwidth loop.
Table 5-1 identifies values for RC and CC for standard
buck inductor (L) and output capacitor (COUT) values.
TABLE 5-1: RC and CC VALUES
L
3.3 µH
COUT
10.0 µF
RC
25 k
CC
1000 pF
2.2 µH
4.7 µF
10 k
1000 pF
5.3 Printed Circuit Board (PCB)
Layout
The MCP1612 is capable of switching over 1A at
1.4 MHz. As with all high-frequency switching power
supplies, good PCB layout techniques are essential to
prevent noise generated by the switching power-train
from interfering with the sensing circuitry.
There are two ground pins (PGND and AGND) on the
MCP1612 to separate the large-signal ground current
from the small-signal circuit ground. These two
grounds should be kept separate, only connecting near
the input bulk capacitor.
Care must also be taken to minimize the length and
loop area of the large signal connections. Components
connected to this loop consist of the input bulk
capacitor, VIN, PGND and LX pins of the MCP1612, the
buck inductor and the output filter capacitor.
2004-2013 Microchip Technology Inc.
DS21921C-page 13
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