Microchip Technology MCP1640RD-4ABC 데이터 시트
2011 Microchip Technology Inc.
DS22234B-page 15
MCP1640/B/C/D
5.0
APPLICATION INFORMATION
5.1
Typical Applications
The MCP1640/B/C/D synchronous boost regulator
operates over a wide input and output voltage range.
The power efficiency is high for several decades of load
range. Output current capability increases with input
voltage and decreases with increasing output voltage.
The maximum output current is based on the N-Chan-
nel peak current limit. Typical characterization curves in
this data sheet are presented to display the typical out-
put current capability.
operates over a wide input and output voltage range.
The power efficiency is high for several decades of load
range. Output current capability increases with input
voltage and decreases with increasing output voltage.
The maximum output current is based on the N-Chan-
nel peak current limit. Typical characterization curves in
this data sheet are presented to display the typical out-
put current capability.
5.2
Adjustable Output Voltage
Calculations
Calculations
To calculate the resistor divider values for the
MCP1640/B/C/D, the following equation can be used.
Where R
MCP1640/B/C/D, the following equation can be used.
Where R
TOP
is connected to V
OUT
, R
BOT
is connected
to GND and both are connected to the FB input pin.
EQUATION 5-1:
Example A:
V
OUT
= 3.3V
V
FB
= 1.21V
R
BOT
= 309 k
R
TOP
= 533.7 k
(Standard Value = 536 k)
Example B:
V
OUT
= 5.0V
V
FB
= 1.21V
R
BOT
= 309 k
R
TOP
= 967.9 k
(Standard Value = 976 k)
There are some potential issues with higher value
resistors. For small surface mount resistors,
environment contamination can create leakage paths
that significantly change the resistor divider that effect
the output voltage. The FB input leakage current can
also impact the divider and change the output voltage
tolerance.
resistors. For small surface mount resistors,
environment contamination can create leakage paths
that significantly change the resistor divider that effect
the output voltage. The FB input leakage current can
also impact the divider and change the output voltage
tolerance.
5.3
Input Capacitor Selection
The boost input current is smoothed by the boost
inductor reducing the amount of filtering necessary at
the input. Some capacitance is recommended to
provide decoupling from the source. Low ESR X5R or
X7R are well suited since they have a low temperature
coefficient and small size. For most applications,
4.7 µF of capacitance is sufficient at the input. For high
power applications that have high source impedance or
long leads, connecting the battery to the input 10 µF of
capacitance is recommended. Additional input
capacitance can be added to provide a stable input
voltage.
inductor reducing the amount of filtering necessary at
the input. Some capacitance is recommended to
provide decoupling from the source. Low ESR X5R or
X7R are well suited since they have a low temperature
coefficient and small size. For most applications,
4.7 µF of capacitance is sufficient at the input. For high
power applications that have high source impedance or
long leads, connecting the battery to the input 10 µF of
capacitance is recommended. Additional input
capacitance can be added to provide a stable input
voltage.
contains the recommended range for the
input capacitor value.
5.4
Output Capacitor Selection
The output capacitor helps provide a stable output
voltage during sudden load transients and reduces the
output voltage ripple. As with the input capacitor, X5R
and X7R ceramic capacitors are well suited for this
application.
voltage during sudden load transients and reduces the
output voltage ripple. As with the input capacitor, X5R
and X7R ceramic capacitors are well suited for this
application.
The MCP1640/B/C/D is internally compensated so
output capacitance range is limited. See
output capacitance range is limited. See
for
the recommended output capacitor range.
While the N-Channel switch is on, the output current is
supplied by the output capacitor C
supplied by the output capacitor C
OUT
. The amount of
output capacitance and equivalent series resistance
will have a significant effect on the output ripple
voltage. While C
will have a significant effect on the output ripple
voltage. While C
OUT
provides load current, a voltage
drop also appears across its internal ESR that results
in ripple voltage.
in ripple voltage.
EQUATION 5-2:
Where dV represents the ripple voltage and dt
represents the ON time of the N-Channel switch (D * 1/
F
represents the ON time of the N-Channel switch (D * 1/
F
SW
).
contains the recommended range for the
input and output capacitor value.
R
TOP
R
BOT
V
OUT
V
FB
----------------
1
–
=
TABLE 5-1:
CAPACITOR VALUE RANGE
C
IN
C
OUT
Min
4.7 µF
10 µF
Max
none
100 µF
I
OUT
C
OUT
dV
dt
-------
=