34844 datasheet(30/36 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34844

TYPICAL APPLICATIONS

COMPONENTS CALCULATION

Slope Compensation

Slope Compensation can be expressed either in terms of

Ampers/Second or as Volts/Second, through the use of the

transfer resistance.

The following formula express the Slope Compensation in

terms of V/μs:

In order to have this slope compensation, the following

resistor should be set.

Variable Definition

D= Boost Duty Cycle

Vout= Output Voltage

VD= Diode Forward Voltage

Vin= Input Voltage

VSW= VDROP of Internal Switch

ΔVout= Output Voltage Ripple Ratio

Iinavg= Average Input Current

Iout= Output Current

Iinmax= Maximum input current

r = Output Current Ripple Ratio

IrmsCin= RMS current for Input Capacitor

IrmsCout= RMS current for Output Capacitor

L= Inductor

rw= Inductor winding DC Resistance

FSW= Boost Switching Frequency

CSG= Current Sense Gain = 0.2 V/A

ACSA= Current Sense Amplifier Gain = 9

RSense= Current Sense Resistor = 22mohm

Cout= Output Capacitor

RComp= Compensation Resistor

GM= OTA Transconductance

ESRCout= ESR of Output Capacitor

fRHPZ= Right Half Plane Zero Frequency

fCross= Crossover Frequency

CComp1= Compensation Capacitor

CComp2= Shunt Compensation Capacitor

VSLOPE= Slope Compensation (V/μs)

RSLOPE= External Resistor for Slope Compensation

CComp2

6.28 FSW

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

VSLOPE

Vout Vin

–

() CSG

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

Where “L” is in μH

RSLOPE

×10

VSLOPE

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

34844 Datasheet(PDF) 30 Page - Freescale Semiconductor, Inc

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