MCP16252 datasheet(14/34 Pages) MICROCHIP

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MCP16251/2

DS25173A-page 14

 2013 Microchip Technology Inc.

5.0

APPLICATION INFORMATION

5.1

Typical Applications

The

MCP16251/2

synchronous

boost

regulator

operates over a wide input voltage and output voltage

range. The power efficiency is high for several decades

of load range. Output current capability increases with

the input voltage and decreases with the increasing

output voltage. The maximum output current is based

the

N-Channel

peak

current

limit.

Typical

characterization

curves

this

data

sheet

are

presented to display the typical output current

capability.

5.2

Adjustable Output Voltage

Calculations

To calculate the resistor divider values for the

MCP16251/2, use Equation 5-1, where RTOP is

connected to VOUT, RBOT is connected to GND and

both are connected to the VFB input pin.

EQUATION 5-1:

EXAMPLE 1:

EXAMPLE 2:

EXAMPLE 3:

The internal Error Amplifier is a transconductance type;

its gain is not related to the resistors’ value. There are

some potential issues with higher value resistors. For

small surface mount resistors, environment contamina-

tion can create leakage paths that significantly change

the resistor divider ratio and change the output voltage

tolerance. Designers should use resistors that are

larger than 1 M

 with precaution; they can be used on

limited temperature range (-20 to +85oC). For a lower

temperature

(down

-40oC),

resistors

from

Examples 1 or 2 are calculated as following:

EXAMPLE 4:

EXAMPLE 5:

Smaller feedback resistor values will increase the

quiescent current drained from the battery by a few µA,

but will result in good regulation over the entire

temperature range.

For boost converters, the removal of the feedback

resistors during operation must be avoided. In this

case, the output voltage will increase above the

absolute maximum output limits of the MCP16251/2

and damage the device (for additional informations,

see AN1337 Application Note).

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.

Table 5-1 contains the recommended range for the

input capacitor value.

VOUT = 2.0V

VFB = 1.23V

RBOT = 1 M

RTOP = 626.01 kwith a standard value of

620 k

 V

OUT is 1.992V)

VOUT = 3.3V

VFB = 1.23V

RBOT = 1 M

RTOP = 1.68 Mwith a standard value of

1.69 M

 V

OUT is 3.308V)

VOUT = 5.0V

VFB = 1.23V

RBOT = 1 M

RTOP = 3.065 M (with a standard value of

3.09 M

 V

OUT is 5.03V)

TOP

BOT

OUT

-------------1

–







VOUT = 2.0V

VFB = 1.23V

RBOT = 309 k

RTOP = 193.44 kwith a standard value of

191 k

 V

OUT is 1.99V)

VOUT = 3.3V

VFB = 1.23V

RBOT = 309 k

RTOP = 520.024 kwith a standard value of

523 k

 V

OUT is 3.311V)

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