MCP19035-AAAAESLASHMF datasheet(22/44 Pages) MICROCHIP

22 / 44 page

MCP19035

DS22326B-page 22

 2012-2013 Microchip Technology Inc.

The low-side MOSFET (synchronous rectifier) is “soft-

commutated” by the energy stored in the inductor , thus

reducing the switching losses. For the low-side transis-

tor, the power losses mainly consist of conduction

losses, body diode conduction losses and body diode

reverse recovery losses.

Similarly to the high-side, the RMS current that pass

through the low-side MOSFET is calculated using

Equation 5-14:

EQUATION 5-14:

RMS CURRENT FOR

LOW-SIDE MOSFET

The conduction losses for low-side MOS transistor are

estimated in Equation 5-15:

EQUATION 5-15:

CONDUCTION LOSSES

FOR LOW-SIDE

TRANSISTOR

The body diode conduction loss is calculated in

Equation 5-16:

EQUATION 5-16:

BODY DIODE

CONDUCTION LOSSES

The body diode recovery time losses will be calculated

using Equation 5-17:

EQUATION 5-17:

BODY DIODE REVERSE

RECOVERY LOSSES

The total power loss for the low-side MOSFET can now

be estimated by summing the power losses in

Equation 5-18:

EQUATION 5-18:

TOTAL POWER LOSS FOR

LOW-SIDE MOSFET (SR)

The conduction losses are the dominant part of the total

losses for the low-side transistor; choose a MOSFET

with a low RDS(on).

The body diode conduction and reverse recovery

losses can be greatly minimized by reducing the Dead

Times necessary to prevent the shoot-through. This

can be achieved by choosing transistors that have a

very low Figure of Merit (FOM) MOSFET for both sides.

5.2.7

BOOTSTRAP CAPACITOR

SELECTION

The selection of the bootstrap capacitor is based upon

the total gate charge of the high-side power MOSFET

and the allowable droop in gate drive voltage while the

high-side power

MOSFET

is conducting (see

Equation 5-19).

EQUATION 5-19:

BOOTSTRAP CAPACITOR

It is recommended that the voltage droop does not

exceed 50 mV. A low ESR, ceramic capacitor, rated at

least 16 VDC, is recommended.

RMS Low-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 Low-Side

RMS Low -Side

2 R

DS on

LS max





LOSS BD

OUT



Where:

VF = Forward Voltage of the Body Diode (V)

tBD = Total Conduction Time for Body Diode (s)



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

Where:

QRR = Reverse Recovery Charge of the Body Diode (C)

Loss Low -Side

COND Low-Side

LOSS BD

BOOT

G Total



V

DROOP

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

Where:

QG(Total) = High-side MOSFET Total Gate Charge (C)

∆VDROOP = Allowable Gate Drive Voltage Droop (V)

MCP19035-AAAAE/MF датащи(PDF) 22 Page - Microchip Technology

MCP19035-AAAAE/MF датащи(HTML) 22 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

датащи скачать

ссылки URL