MIC2133 datasheet(38/50 Pages) MICROCHIP

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DS20006653B-page 38

MIC2133

The output voltage is determined by the equation

below:

EQUATION 5-37:

A typical value of R1 can be between 3 kΩ and 10 kΩ.

If R1 is too large, it may allow noise to be introduced

into the voltage feedback loop. If R1 is too small, it

decreases the efficiency of the buck converter,

especially at light loads. After R1 is selected, R2 can be

calculated using the formula below.

EQUATION 5-38:

5.7

Secondary Phase Shedding On

and Off

The output load currents at which the secondary phase

will be turned on and off can be estimated with the

equation below.

EQUATION 5-39:

5.8

AVP Droop Load Line Resistance

The AVP Droop load line resistance can be calculated

by the equation below.

EQUATION 5-40:

5.9

Power Dissipation in MIC2133

The MIC2133 features two Low-Dropout (LDO)

regulators to supply power at the PVDD pin from either

VIN or EXTVDD, depending on the voltage at the

EXTVDD pin. PVDD powers the MOSFET drivers and

VDD pin, which powers the internal circuitry and is

recommended to connect to PVDD through a low-pass

filter. In applications where the output voltage is 5V and

above (up to 14V), it is recommended that the EXTVDD

be connected to the output to reduce the power dissi-

pation in the MIC2133 to reduce the MIC2133 junction

temperature and to improve the system efficiency. The

power dissipation in the MIC2133 depends on the inter-

nal LDO being in use, gate charge of the external MOS-

FETs and switching frequency. The power dissipation

and the junction temperature of the MIC2133 can be

estimated using the equation below, Equation 5-42 and

Equation 5-43.

Power dissipation in the MIC2133 is calculated in the

equation below when EXTVDD is not used.

EQUATION 5-41:

VOUT

VREF

-------







Where:

VREF =0.6V

VREF R1



VOUT VREF

–

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

ILOAD SECON



1.2V VPSH

–

4RSENSE



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





I

LPP



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





–



ILOAD SECOFF



0.8V

1.2V VPSH

–





4RSENSE



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



 I

LPP



–



Where:

ILOAD(SECON) = Load Current at which the Secondary

Phase will be Turned On

ILOAD(SECOFF) = Load Current at which the Secondary

Phase will be Turned Off

VPSH = Voltage at the PSH Pin

∆IL(PP) = Peak-to-Peak Ripple Inductor Current

RSENSE = Current Sense Resistance: Either

Fixed Sense Resistor or Low-Side

MOSFET RDS(ON)

RLOADLINE

V

OUT DROOP



I

LPK



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

4RSENSE



RDROOP

RFBB2

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

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

VREF

VOUT

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

–





 VOUT

VREF

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



Where:

∆VOUT(DROOP) = Change in Output Voltage with Load

∆IL(PK) = Total Change in Peak Inductor

Current for All Phases for a given

Change in Load Current

RSENSE = Current Sense Resistance

VREF = Reference Voltage (0.6V typical)

VOUT = Output Voltage

RDROOP = Resistance of Droop Setting Resistor

Connected at the DROOP Pin

RFBB2 = Lower Bottom Feedback Resistance

Value

PIC

VIN

IGTOTAL





Where:

IG(TOTAL) = Total Average Gate Drive Current for All

Phases

IQ = Quiescent Current of MIC2133

QG(HS1),

QG(LS1)

= Gate Charge of High-Side and

Low-Side MOSFETs in Phase 1

QG(HS2),

QG(LS2)

= Gate Charge of High-Side and

Low-Side MOSFETs in Phase 2

IGTOTAL



QGHS1

 QGLS1

 QGHS2

 QGLS2





f

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