LED5000 datasheet(13/52 Pages) STMICROELECTRONICS

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LED5000

Application notes - buck conversion

Doc ID 023951 Rev 1

13/51

Application notes - buck conversion

5.1

Closing the loop

Figure 6.

Block diagram of the loop

5.2

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 RLOAD represents the load resistance (see Chapter 5.4), RCS 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 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

GCO(s)

AO(s)

αα

LED

AM13490v1

CO s

()

LOAD

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

⋅

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

–

() 0.5

–

⋅

[]

⋅

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

-----

⎝⎠

⎛⎞

-----

⎝⎠

⎛⎞

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

H s

()

⋅⋅

⋅

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