MCP19035-AAAAESLASHMF datasheet(21/44 Pages) MICROCHIP

21 / 44 page

 2012-2013 Microchip Technology Inc.

DS22326B-page 21

MCP19035

5.2.6

MOSFETS SELECTION

Choosing the right MOSFET is a critical part of the

design for a switching regulator. Their performance will

directly impact the efficiency and reliability of the

regulator.

The MCP19035 synchronous buck controller offers an

integrated, logic-level MOSFET driver, and is capable

of supplying 5V to drive the MOSFET gates. As a

result, logic-level MOSFETs must be used. Suitable

MOSFETs should meet the requirement of voltage and

current rating.

A key parameter for evaluating the MOS transistor

performance is the Figure of Merit. For a given

MOSFET, this is defined as the product between the

Total Gate Charge (QG) and RDS(ON) (see Equation 5-

8).

EQUATION 5-8:

FIGURE OF MERIT

A lower FOM value means a higher-performance MOS

transistor.

For the high-side MOSFET, power losses consist of

both switching and conduction losses. Conduction

losses are high when the duty cycle of the converter is

high. The conduction loss of the high-side MOSFET

can be estimated by multiplying the RDS(ON) with the

RMS value of the current that passes through the tran-

sistor (see Equation 5-9).

EQUATION 5-9:

RMS VALUE FOR

HIGH-SIDE CURRENT

The conduction losses for high-side MOS transistor are

estimated in Equation 5-10:

EQUATION 5-10:

CONDUCTION LOSSES

FOR HIGH-SIDE MOSFET

The switching losses are more difficult to calculate,

since they depend on many parameters. Equation 5-11

shows an estimation of these losses:

EQUATION 5-11:

SWITCHING LOSSES FOR

HIGH-SIDE MOSFET

The ts(HL) and ts(LH) times can be estimated using the

following equations:

EQUATION 5-12:

The total power losses for the high-side MOSFET can

be calculated with Equation 5-13:

EQUATION 5-13:

TOTAL POWER LOSSES

FOR HIGH-SIDE MOSFET

For applications that operate with low duty cycle (lower

than 30%) or high input voltage, the power losses for

the high-side transistor are mainly switching losses.

For these applications, it is recommended to choose a

MOSFET that offers a low Total Gate Charge.

For applications that operate with duty cycles higher

than 50%, the power losses for the high-side transistor

are mainly conduction losses. For these applications,

choose a MOSFET that has a low RDS(on).

FOM

GTot





RMS High-Side

OUT

Ripple

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









Where:

D = Duty Cycle

IOUT = Output Current (A)

IRipple = Current Ripple in the Inductor

(typically 30% of the maximum output

current) (A)

CON D High-Side

RMS High-Side

DS on

HS max





SW High-Side

OUT



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





sHL



sLH





Where:

VIN = Input Voltage (V)

IOUT = Output Current (A)

fSW = Switching Frequency (Hz)

ts(HL) = MOSFET Switching Time

(High-to-Low transition) (s)

ts(LH) = MOSFET Switching Time

(Low-to-High transition) (s)

sHL



G Total



DRV

Sink

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

sLH



G Total



DRV

Sour ce

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

Where:

QG(Total) = High-side MOSFET Total Gate

Charge

IDRVSink = Sink Peak Current for High-Side

Driver (typical 1A)

IDRVSource = Source Peak Current for High-Side

Driver (typical 1A)

Loss High-Side

COND High-Side

SW High-Side

MCP19035-AAAAE/MF 数据表(PDF) 21 Page - Microchip Technology

MCP19035-AAAAE/MF 数据表(HTML) 21 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

数据表下载

链接网址

MCP19035-AAAAE/MF 数据表(PDF) 21 Page - Microchip Technology

MCP19035-AAAAE/MF 数据表(HTML) 21 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

数据表 下载

链接网址

数据表下载