Datasheet

MCP1650/51/52/53
DS21876B-page 16  2004-2013 Microchip Technology Inc.
5.1.2 BOOTSTRAP BOOST
APPLICATIONS
For bootstrap configurations, the higher-regulated
boost output voltage is used to power the MCP1650/
51/52/53. This provides a constant higher voltage used
to drive the external MOSFET. The R-option devices
(UVLO < 2.0V) can be used for applications that need
to start up with the input voltage below 2.7V. For this
type of application, the MCP1650/51/52/53 will start off
of the lower 2.0V input and begin to boost the output up
to its regulated value. As the output rises, so does the
input voltage of the MCP1650/51/52/53. This provides
a solution for 2-cell alkaline inputs for output voltages
that are less than 6V.
FIGURE 5-2: Bootstrap Application Circuit MCP1650/51/52/53.
5.1.3 SEPIC CONVERTER
APPLICATIONS
In many applications, the input voltage can vary above
and below the regulated output voltage. A standard
boost converter cannot be used when the output volt-
age is below the input voltage. In this case, the
MCP1650/51/52/53 can be used as a SEPIC controller.
A SEPIC requires 2 inductors or a single coupled
inductor, in addition to an AC coupling capacitor. As
with the previous boost-converter applications, the
SEPIC converter can be used in either a bootstrap or
non-bootstrap configuration. The SEPIC converter can
be a very popular topology for driving high-power
LEDs. For many LEDs, the forward voltage drop is
approximately 3.6V, which is between the maximum
and minimum voltage range of a single-cell Li-Ion
battery, as well as 3 alkaline or nickel metal batteries.
FIGURE 5-3: SEPIC Converter Application Circuit MCP1650/51/52/53.
FB
CS
SHDN
V
IN
8
2
5
6
4
7
MCP1652
GND
Input
Voltage
2.8V to 4.2V
C
in
47 µF
off
on
EXT
3.3 µH
3.09 k
Vout = 5V
Iout = 1A
1k
Li-Ion Input to 5.0V 1A Regulated Output (Bootstrap) with MCP1652 Power Good Output
1
3
NC
PG
0.1 µF
10 
Power Good Output
C
out
47 µF
Ceramic
0.1
Shutdown
N-Channel
MOSFET
Schottky Diode
FB
CS
SHDN
V
IN
8
2
5
6
4
7
MCP1651
GND
Input
Voltage
2.8V to 4.2V
C
IN
47 µF
off
on
EXT
3.3 µH
2.49 k
I
OUT = 1A
1k
Li-Ion Input to 3.6V 3W LED Driver (SEPIC Converter)
1
3
NC
PG
0.1 µF
10 
Power Good Output
4.7 µF
3.3 µH
0.2 
C
OUT
47 µF
Ceramic
0.1
3W
LED
Dimming Capability
Schottky Diode
N-Channel
MOSFET