MIC2132 datasheet(34/48 Pages) MICROCHIP

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MIC2132

DS20006654B-page 34

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The RMS current rating of the high-side power

MOSFET in each phase channel is approximated in

Equation 5-24.

EQUATION 5-24:

The maximum duty cycle of each phase channel is

calculated in Equation 5-25:

EQUATION 5-25:

The RMS current rating of the low-side power MOSFET

each

phase

channel

approximated

Equation 5-26.

EQUATION 5-26:

The conduction loss of the high-side power MOSFET in

each phase channel is calculated in Equation 5-27.

EQUATION 5-27:

The conduction loss of the low-side power MOSFET in

each phase channel is calculated in Equation 5-28.

EQUATION 5-28:

The switching loss of the high-side power MOSFET in

each phase channel is estimated in Equation 5-29.

EQUATION 5-29:

The high-side MOSFET output capacitance discharge

loss can be calculated in Equation 5-30.

EQUATION 5-30:

The total power dissipation of the high-side power

MOSFET in each phase channel is the sum of the con-

duction loss, the switching loss and the MOSFET output

capacitance discharge loss, as shown in Equation 5-31.

EQUATION 5-31:

The high-side power MOSFET in each phase channel

selected must be capable of handling the total power

dissipation. To improve efficiency and minimize the

power loss, the power MOSFET should be selected

with low on-resistance and optimum gate charge.

Where:

DMAX = Maximum Duty Cycle

ISWHS(RMS) =

DMAX

IOUT(MAX)

√

Where:

VOUT(MAX) = Maximum Output Voltage

VIN(MIN) = Minimum Input Voltage

Eff = Efficiency of Buck Converter

DMAX =

VOUT(MAX)

Eff × VIN(MIN)

Where:

DMAX = Maximum Duty Cycle

ISWLS(RMS) =

1 – DMAX

IOUT(MAX)

√

Where:

RDSON(HS) = High-Side MOSFET On-Resistance

PCOND(HS) = ISWHS(RMS)2 × RDSON(HS)

Where:

RDSON(LS) = Low-Side MOSFET On-Resistance

PCOND(LS) = ISWLS(RMS)2 × RDSON(LS)

Where:

tR = High-Side MOSFET Turn-on Transition Time

tF = High-Side MOSFET Turn-off Transition Time

QG(HS) = Switching Gate Charge of High-Side

MOSFET

QGSHS = Gate-to-Source Charge of High-Side

MOSFET

QGDHS = Gate-to-Drain Charge of High-Side MOSFET

RONDHH = High-Side Gate Driver Pull-up Resistance

RONDHL = High-Side Gate Driver Pull-Down

Resistance

RG(HS) = Gate Resistance of High-Side MOSFET

VTH(HS) = High-Side MOSFET Gate-to-Source

Threshold Voltage

PSWL(HS) = VIN(MAX) ×

IOUT(MAX)

× (tR + tF) × fSW

tR = QG(HS) ×

(RONDHH + RG(HS))

VDD – VTH(HS)

tF = QG(HS) ×

(RONDHL + RG(HS))

VTH(HS)

QG(HS) = 0.5 × QGSHS + QGDHS

Where:

COSS(HS) = High-Side MOSFET Output Capacitance

PCOSS(HS) = 0.5 × COSS(HS)(VIN(MAX))2 × fSW

PD(HS) = PCOND(HS) + PSWL(HS) + PCOSS(HS)

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