MCP1612 Microchip Technology, MCP1612 Datasheet - Page 13

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

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Solving for C:
There will also be some ripple voltage caused by the
ESR of the capacitor. The ripple is defined as follows.
EQUATION 5-7:
For this example:
5.2.4
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 V
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
The V
circuitry. A 10
unregulated inputs V
capacitor to ground to help isolate the V
switching noise.
© 2005 Microchip Technology Inc.
Where:
V
V
CC
ESRRIPPLE
ESRRIPPLE
V
I
input is used to bias the internal MCP1612
C
C
t = on-time of P-channel MOSFET
INPUT CAPACITOR
V
V
V
V
ESR = 8 m
= peak-to-peak ripple current
= output ripple voltage
CC
OUT
OUT
OUT
IN
V
V
V
I
C = 4.7 µF
C
C
C
and P
resistor is recommended between the
ESRRIPPLE
t = 260 ns
INPUT
= 165 mA
= (260 ns x 165 mA)/4.7 µF
= 9.13 mV
= 8 m x 165 mA
= 1.32 mV
=
= 9.13 mV + 1.32 mV
= 10.45 mV
C
IN
GND
=
V
and V
I
C
C
is recommended to filter the
+ V
=
---------- -
ESR
CC
ESRRIPPLE
V
t
C
, along with a 0.1 µF
I
C
CC
pin from the
5.2.6
An internal transconductance error amplifier is used to
compensate the buck converter. An external resistor
(R
and GND, are all that is needed to provide a high-
bandwidth loop.
Table 5-1 identifies values for R
buck inductor (L) and output capacitor (C
TABLE 5-1:
5.3
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 (P
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, V
buck inductor and the output filter capacitor.
C
3.3 µH
2.2 µH
) and capacitor (C
L
Printed Circuit Board (PCB)
Layout
COMPENSATION COMPONENTS
IN
, P
10.0 µF
GND
4.7 µF
C
R
OUT
C
and L
and C
C
), connected between COMP
X
C
pins of the MCP1612, the
VALUES
MCP1612
GND
25 k
10 k
C
R
and C
C
and A
DS21921B-page 13
C
OUT
GND
for standard
1000 pF
1000 pF
) values.
C
) on the
C