MCP16301T-ESLASHCH datasheet(17/38 Pages) MICROCHIP

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DS20005004E-page 19

MCP16301/H

5.0

APPLICATION INFORMATION

5.1

Typical Applications

The MCP16301/H step-down converters operate over

a wide input voltage range, up to 36V maximum.

Typical applications include generating a bias or VDD

voltage for the PIC® microcontroller product line, digital

control system bias supply for AC-DC converters, 24V

industrial input and similar applications.

5.2

Adjustable Output Voltage

Calculations

To calculate the resistor divider values for the

MCP16301/H devices, Equation 5-1 can be used.

RTOP is connected to VOUT, RBOT is connected to GND

and both are connected to the VFB input pin.

EQUATION 5-1:

EXAMPLE 5-1:

EXAMPLE 5-2:

The transconductance error amplifier gain is controlled

by its internal impedance. The external resistor dividers

have no effect on system gain, so a wide range of

values can be used. A 10 k

 bottom resistor is

recommended as a good trade-off for quiescent current

and noise immunity.

5.3

General Design Equations

The step-down converter duty cycle can be estimated

using Equation 5-2 while operating in Continuous

Inductor Current mode. This equation also counts the

forward drop of the freewheeling diode and internal

N-Channel MOSFET switch voltage drop. As the load

current increases, the switch voltage drop and diode

voltage drop increase, requiring a larger PWM duty

cycle to maintain the output voltage regulation. Switch

voltage drop is estimated by multiplying the switch

current times the switch resistance (or RDSON).

EQUATION 5-2:

CONTINUOUS INDUCTOR

CURRENT DUTY CYCLE

The MCP16301/H devices feature an integrated slope

compensation to prevent the bimodal operation of the

PWM duty cycle. Internally, half of the inductor current

down slope is summed with the internal current sense

signal. For the proper amount of slope compensation,

it is recommended to keep the inductor down-slope

current constant by varying the inductance with VOUT,

where K = 0.22V/µH.

EQUATION 5-3:

For

VOUT = 3.3V, an inductance of 15 µH is

recommended.

TOP

BOT

OUT

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

–







VOUT

=3.3V

VFB

=0.8V

RBOT

=10 k



RTOP

31.25 k

 (standard value = 31.6 k)

VOUT

3.328V (using standard value)

VOUT

=5.0V

VFB

=0.8V

RBOT

=10 k



RTOP

52.5 k

 (standard value = 52.3 k)

VOUT

4.98V (using standard value)

TABLE 5-1:

RECOMMENDED INDUCTOR

VALUES

VOUT

KLSTANDARD

2.0V

0.20

10 µH

3.3V

0.22

15 µH

5.0V

0.23

22 µH

12V

0.21

56 µH

15V

0.22

68 µH

OUT

Diode



DSON





–



-------------------------------------------------------

OUT L



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