Datasheet

LED5000 Application notes - buck conversion
Doc ID 023951 Rev 1 13/51
5 Application notes - buck conversion
5.1 Closing the loop
Figure 6. Block diagram of the loop
5.2 G
CO
(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 R
LOAD
represents the load resistance (see Chapter 5.4 ), R
CS
the equivalent sensing
resistor of the current sense circuitry, ω
p
the single pole introduced by the LC filter and ω
z
the
zero given by the ESR of the output capacitor.
F
H
(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.
V
IN
-
+
-
LC filter
V
REF
error
amplifier
FB
compensation
network
PWM
comparator
HS
switch
R
S
L
C
OUT
R
C
C
C
+
PWM control
Current sense
LS
switch
V
OUT
V
CONTROL
G
CO
(s)
A
O
(s)
αα
LED
AM13490v1
G
CO
s()
R
LOAD
R
CS
------------------
1
1
R
0
T
SW
⋅
L
------------------------- -
m
C
1D–()0.5–⋅[]⋅+
-------------------------------------------------------------------------------------------------
1
s
ω
z
-----+
⎝⎠
⎛⎞
1
s
ω
p
-----+
⎝⎠
⎛⎞
---------------------
F
H
s()⋅⋅⋅=