MCP16311SLASH2 datasheet(19/40 Pages) MICROCHIP

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 2013-2019 Microchip Technology Inc.

DS20005255C-page 19

MCP16311/2

5.0

APPLICATION INFORMATION

5.1

Typical Applications

The MCP16311/2 synchronous step-down converter

operates over a wide input range, up to 30V maximum.

Typical applications include generating a bias or VDD

voltage for PIC® microcontrollers, digital control system

bias supply for AC-DC converters and 12V industrial

input and similar applications.

5.2

Adjustable Output Voltage

Calculations

To calculate the resistor divider values for the

MCP16311/2 adjustable version, use Equation 5-1.

RTOP is connected to VOUT, RBOT is connected to

AGND, and both are connected to the VFB input pin.

EQUATION 5-1:

RESISTOR DIVIDER

CALCULATION

EXAMPLE 5-1:

3.3V RESISTOR DIVIDER

EXAMPLE 5-2:

5.0V RESISTOR DIVIDER

EXAMPLE 5-3:

12.0V RESISTOR DIVIDER

The error amplifier is internally compensated to ensure

loop stability. External resistor dividers, inductance and

output capacitance all have an impact on the control

system and should be selected carefully and evaluated

for stability. A 10 kΩ 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 accounts for the

forward drop of the two internal N-Channel MOSFETS.

As load current increases, the voltage drop in both

internal switches will 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 MCP16311/2 device features an integrated slope

compensation to prevent 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 = 0.22 V/µH.

EQUATION 5-3:

For example, for VOUT = 3.3V, an inductance of 15 µH

is recommended.

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 = 4.984V (using standard values)

VOUT =12.0V

VFB =0.8V

RBOT =10 k

RTOP =140 k (standard value = 140 k)

RTOP

RBOT

VOUT

VFB

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

–







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

24V

0.24

100 µH

VOUT

ILSW RDSONL





VIN

IHSW RDSONH





–

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

KVOUT L



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