MCP19035-AAAAESLASHMF datasheet(19/44 Pages) MICROCHIP

19 / 44 page

 2012-2013 Microchip Technology Inc.

DS22326B-page 19

MCP19035

5.0

APPLICATION INFORMATION

5.1

Typical Applications

The MCP19035 synchronous buck controller operates

over an input voltage range up to a maximum of 30V.

The output current capability depends only on the

external MOSFET’s selection and can also be very

high, typically up to 20A.

Typical applications include POL modules for powering

DSPs, FPGAs and ASICs, and, in general, any step-

down voltage conversion (from maximum 30V input

voltage) for medium-to-high output current loads.

5.2

Design Procedure

To simplify this design process, an Excel®-based

design tool is available to support typical applications.

This tool is available on the MCP19035 product web

site. Refer to AN1452 – “Using the MCP19035

Synchronous Buck Converter Design Tool”

for further

details.

5.2.1

SWITCHING FREQUENCY AND THE

MAXIMUM CONVERSION RATIO

The MCP19035 controller provides two options for the

switching frequency: 300 kHz and 600 kHz. In general,

choosing a higher switching frequency allows the use

of smaller size components (i.e. inductor and filtering

capacitors), but increases the switching losses. The

300 kHz switching frequency is recommended for

applications requiring output currents up to 20A. For

applications requiring output currents up to 10A, the

recommended switching frequency is 600 kHz.

Due to the minimum “On Time” for the high-side

MOSFET driver (70 ns typical), the maximum

conversion ratio must be limited to 20:1.

5.2.2

DEAD TIME SELECTION

Dead Time will affect the maximum obtainable

efficiency of the converter. Selecting the Dead Time

depends on the external MOSFETs’ parameters. Lower

Figure of Merit (FOM) transistors will permit the use of

shorter Dead Times. This may increase the converter

efficiency by up to 2%.

Low Figure of Merit transistors allow the user to select

a low value for Dead Time (typical 12 ns) without

causing a shoot-through phenomenon. For low-FOM

transistors, the MCP19035 version with fixed 12 ns

Dead Time is recommended.

For typical medium Figure of Merit transistors, the

MCP19035 version with the adaptive Dead-Time

generator is recommended.

5.2.3

INDUCTOR SELECTION

The output inductor is responsible for smoothing the

square wave created by the switching action and for

controlling the output current ripple (∆IOUT). There is a

trade off between efficiency and load transient

response time when the value of the inductor is

chosen. The smaller the inductance, the quicker the

converter can respond to transients in the load current.

However, a smaller inductor requires a higher switching

frequency to maintain the same level of output current

ripple. Remember that increasing the switching

frequency will also increase the switching losses in the

MOSFETs.

A good compromise for the inductor current ripple is

30% of the output current. The value of the inductor is

calculated in Equation 5-1:

EQUATION 5-1:

INDUCTOR VALUE

The peak current in the inductor is determined in

Equation 5-2:

EQUATION 5-2:

INDUCTOR PEAK

CURRENT

EQUATION 5-3:

INDUCTOR RMS

CURRENT

Additional care must be taken when selecting an induc-

tor:

• Choose an inductor that has a saturation current

larger than the calculated peak current. The

tolerance of the inductor must also be considered

(typically 20%).

• To minimize the conduction losses, choose an

inductor with the lowest possible DC resistance.

The maximum DC resistance specified in the data

sheet will ensure the worst-case component spec-

ification.

• There are many magnetic materials available for

inductor core: ferrite, iron powder and composite

materials. The ferrite offers the lowest core

losses, but the saturation characteristic is “hard”

(i.e. the inductance drops rapidly after the current

reaches the saturation level). The losses of iron

powder or composite material cores are higher

than ferrite, but the saturation characteristic is

“soft”, making it more suitable for voltage mode

control converter, including the MCP19035.

MAX

OUT

–





OUT

MAX

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



----------

0.3

OUT

MAX



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



PEAK

OUT

MAX

0.3

OUT

MAX



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

RM S

OUT

Ripple

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

MCP19035-AAAAE/MF Datasheet(PDF) 19 Page - Microchip Technology

MCP19035-AAAAE/MF Datasheet(HTML) 19 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

Datasheet Descarga

Enlace URL