Microchip Technology ARD00386 数据表
Installation and Operation
© 2011 Microchip Technology Inc.
DS51999A-page 17
FIGURE 2-5:
MCP1640 12V/50 mA Two Cells Input Boost Converter
Reference Design Test Points (SWH, SWL), Inductor (I
L
) and Load Current (I
OUT
)
Waveforms for 60 mA Load and 2.4V Input in Continuous mode.
2.2.3
How Does the MCP1640 12V/50 mA Two Cells Input Boost
Converter Reference Design Works?
Converter Reference Design Works?
The board was designed to boost low voltage from two alkaline cells or NiCd/NiMH
cells to high voltage. The topology used in this reference design is adapting a
low-voltage boost converter into a high-voltage boost converter using a single inductor,
instead of using a flyback topology that requires a more expensive flyback transformer.
Another advantage is that the switching voltage spikes are kept below the safe value,
6V, for MCP1640 device’s SW pin.
cells to high voltage. The topology used in this reference design is adapting a
low-voltage boost converter into a high-voltage boost converter using a single inductor,
instead of using a flyback topology that requires a more expensive flyback transformer.
Another advantage is that the switching voltage spikes are kept below the safe value,
6V, for MCP1640 device’s SW pin.
The converter is configured as nonsynchronous; an external diode, D, is connected
between the inductor and the high-voltage output (V
between the inductor and the high-voltage output (V
OUT
).
The two sense resistors, R
T
and R
B
, set the output (V
OUT
) at 12.0V according to the
following equation:
EQUATION 2-1:
R
T
R
B
V
OUT
V
FB
-------------
1
–
⎝
⎠
⎛
⎞
×
=
Where:
V
FB
=
1.21V
V
FB
=
Reference voltage of the FB pin
V
OUT
=
12.0V
R
B
=
Resistor’s value is selected by the designer
Note:
The reference board is tested up to 24V output with a maximum load of
20 mA. The internal error amplifier is a transconductance type; its gain is
not related to the feedback resistors’ values.
20 mA. The internal error amplifier is a transconductance type; its gain is
not related to the feedback resistors’ values.