MIC2133 datasheet(36/50 Pages) MICROCHIP

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DS20006653B-page 36

MIC2133

The maximum duty cycle of each phase channel is

calculated in the equation below:

EQUATION 5-25:

The RMS current rating of the low-side power MOSFET

in each phase channel is calculated in the equation

below.

EQUATION 5-26:

The conduction loss of the high-side power MOSFET in

each phase channel is calculated in the equation below.

EQUATION 5-27:

The conduction loss of the low-side power MOSFET in

each phase channel is calculated in the equation below.

EQUATION 5-28:

The switching loss of the high-side power MOSFET in

each phase channel is estimated in the equation below.

EQUATION 5-29:

The high-side MOSFET output capacitance discharge

loss can be calculated in the equation below.

EQUATION 5-30:

The total power dissipation of the high-side power

MOSFET in each phase channel is the sum of the

conduction loss, the switching loss and the MOSFET

output capacitance discharge loss, as shown in the

equation below.

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, it is recommended that the power MOSFET

be selected with low on-resistance and optimum gate

charge. On the other hand, the power dissipation in the

DMAX

VOUT MAX



Eff VIN MIN





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

Where:

VOUT(MAX) = Maximum Output Voltage

VIN(MIN) = Minimum Input Voltage

Eff = Efficiency of Buck Converter

ISWLS RMS



IOUT MAX



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

1 D

– MAX



Where:

DMAX = Maximum Duty Cycle

Where:

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

PCOND HS



ISWHS RMS



RDSON HS





PCOND LS



ISWLS RMS



RDSON LS





Where:

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

PSWL HS



VIN MAX



IOUT MAX



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



tR tF





fSW



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

QGHS



RONDHH RGHS



VDD VTH HS



–

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



QGHS



RONDHL RGHS



VTH HS



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



QGHS



0.5 QGSHS QGDHS



PCOSS HS



0.5 COSS HS

 VIN MAX



fSW



Where:

COSS(HS) = High-Side MOSFET Output Capacitance

PDHS



PCOND HS



PSWL HS



PCOSS HS



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