MCP1650/51/52/53

DS21876A-page 16

 2004 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

8

2

5

6

4

7

MCP1652

GND

Input

Voltage

2.8V to 4.2V

47 µF

off

on

EXT

3.3 µH

3.09 k

Ω

Vout = 5V

Iout = 1A

1k

Ω

Li-Ion Input to 5.0V 1A Regulated Output (Bootstrap) with MCP1652 Power Good Output

1

3

NC

PG

0.1 µF

10

Ω

Power Good Output

47 µF

Ceramic

0.1

Ω

Shutdown

N-Channel

MOSFET

Schottky Diode

FB

CS

SHDN

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

Ω

1k

Ω

Li-Ion Input to 3.6V 3W LED Driver (SEPIC Converter)

1

3

NC

PG

0.1 µF

10

Ω

Power Good Output

4.7 µF

3.3 µH

0.2

Ω

C

OUT

47 µF

Ceramic

0.1

Ω

3W

LED

Dimming Capability

Schottky Diode

N-Channel

MOSFET