LED2001 datasheet(12/42 Pages) STMICROELECTRONICS

12 / 42 page

Application notes

LED2001

12/42

DocID024346 Rev 1

Application notes

6.1

Closing the loop

Figure 5. Block diagram of the loop

6.2

GCO(s) control to output transfer function

The accurate control to output transfer function for a buck peak current mode converter can

be written as:

Equation 1

where R0 represents the load resistance, Ri the equivalent sensing resistor of the current

sense circuitry,

ωp the single pole introduced by the LC filter and ωz the zero given by the

ESR of the output capacitor.

FH(s) accounts for the sampling effect performed by the PWM comparator on the output of

the error amplifier that introduces a double pole at one half of the switching frequency.

VIN

LC filter

VREF

error

amplifier

compensation

network

PWM

comparator

switch

COUT

PWM control

Current sense

switch

VOUT

VCONTROL

CO(s)

O(s)

LED

CO s

()

-------

⋅

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

–

() 0.5

–

⋅

[]

⋅

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

------





------





---------------------- FH s

()

⋅⋅

⋅

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