Analog Integrated Circuit Device Data



28

Freescale Semiconductor

34844

TYPICAL APPLICATIONS

COMPONENTS CALCULATION

The output capacitor should handle at least the following RMS current.

Network Compensation

Since this Boost converter is current controlled, Type II compensation is needed.

To calculate the Network Compensation, first calculate all Boost Converter components.

For this type of compensation, push out the Right Half Plane Zero to higher frequencies where they can’t significantly affect the overall

loop.

The Crossover frequency must be set much lower than the location of the Right half plane zero

Since the system has a fixed Slope, compensation set by RSLOPE, RCOMP should be fixed for all configurations.

CCOMP1 and CCOMP2 should be calculated as follows:

To improve the transient response of the boost, on the 34844, a resistor divider is implemented from the PWM pin to ground with a

connection to the compensation network. This configuration should inject a 1.0 V signal to the COMP pin and the Thevenin-equivalent

resistance of the divider is close to RCOMP, i.e. RCOMP = 6.8 k and RPCOMP= 27 k for a 5.0 V PWM signal.

ESRCout

Vout

Vout FSW L









Vout

1 D

–





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

=

IrmsCout Iout

D

1D

–

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



=

fRHPZ

Vout

1 D

–



2



Iout 2

 L







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

=

fCross

fRHPZ

5

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

=

RComp 5.6kohm

=

CComp1

2

fCross RComp  2







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

=

CComp2

GM

6.28 FSW



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

=

PWM

COMP PIN

RPCOMP

RCOMP

CCOMP1

CCOMP2