FAN5069 Fairchild Semiconductor, FAN5069 Datasheet - Page 17

• Manufacturer Part Number: FAN5069
• Description: The FAN5069 combines a high efficiency Pulse-Width-Modulated PWM controller and a LDO (Low DropOut) linear regulator controller
• Manufacturer: Fairchild Semiconductor

FAN5069 Rev. 1.1.5
© 2005 Fairchild Semiconductor Corporation
Poles and Zeros of Plant Transfer Function:
Plant zero frequency =
Plant 1
Plant 2
Plant 3
Plant gain (magnitude) response:
Plant phase response:
Choose R1, R
loop. Typically F
Calculate plant gain at F
vide to get the required crossover is given by:
The phase boost required is calculated as given in (EQ. 35)
where M is the desired phase margin in degrees.
The feedback component values are calculated as given in equations below:
G
C3
R2
∠
K
Phase Boost
C2
C1
R3
G
G
AMP
p
=
P
=
=
(f)
=
=
=
(f)
⎧
⎨
⎩
--------------------------------------------------------------- -
2 π
------------------------------------------------- -
2 π
----------------------------------------------------------------------- -
2
----------------- -
(
Tan
st
nd
rd
C2
=
K 1
=
×
×
×
R1
=
pole frequency =
pole frequency =
–
pole frequency =
------------------------------- -
20
π F
G
×
tan
×
×
×
⎛
⎝
p
(
)
×
Boost
--------------- -
F
F
K 1
(F
–
BIAS
=
cross
cross
log
1
cross
1
–
K
4
⎛ ⎞
⎝ ⎠
cross
cross
M
--- -
f
1
f
z
M
)
–
1
⎞
⎠
to set the output voltage using EQ.6. Choose the zero crossover frequency F
0
×
×
×
–
∠
should be less than fifth of F
+
)
+
C1
tan
G
G
45
10
K
f
AMP
z
P
cross
–
×
(F
=
1
f
×
⎫
⎬
⎭
f
p1
f
R3
⎛
⎝
p3
2
p2
cross
log
------ -
f
----------------------------------------- -
2
×
p1
f
using EQ.34 by substituting F
R1
×
=
=
=
⎞
⎠
π C
--------------------------------------------------------------------------------------------------------- -
–
---------------------------------------------------------- -
2
)
------------------------- -
2 π
------------
2
1
×
–
ω
tan
×
×
1
×
+
1
2
n
90°
π
π
⎛
⎝
o
×
–
------ -
f
×
×
1
×
×
p1
L
f
⎛
⎝
⎛
⎝
R
⎛
⎝
e
R
------ -
f
⎞
⎠
C
p2
------------------- -
C
f
p
2
es
o
1
o
⎞
⎠
×
×
1
×
–
R
R
–
1
p
tan
1
L
sw
+
+
+
+
. Choose the desired phase margin; typically between 60° to 90°.
------ -
R
⎛
⎝
–
L
⎛ ⎞
⎝ ⎠
R
------ -
L
------ -
f
1
e
--- -
f
L
p2
f
f
⎛
⎝
e
z
p
⎞
⎠
------ -
f
⎞
⎠
⎞
⎠
p3
f
2
2
⎞
⎠
17
×
cross
1
+
in place of f. The gain that the amplifier needs to pro-
⎛
⎝
------ -
f
p3
f
⎞
⎠
2
cross
of the overall
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(EQ. 28)
(EQ. 29)
(EQ. 30)
(EQ. 31)
(EQ. 32)
(EQ. 33)
(EQ. 34)
(EQ. 35)
(EQ. 36)
(EQ. 37)
(EQ. 38)
(EQ. 39)
(EQ. 40)
(EQ. 41)