FAN5099 Fairchild Semiconductor, FAN5099 Datasheet - Page 17

• Manufacturer Part Number: FAN5099
• Description: PWM and ULDO Controller Combo
• Manufacturer: Fairchild Semiconductor

FAN5099 Rev. 1.0.1
© 2006 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
be between 60° to 90°.
Calculate plant gain at F
vide to get the required crossover is given by:
The phase boost required is calculated as given in (EQ. 33).
where M is the desired phase margin in degrees.
The feedback component values are now calculated as given in equations below:
C3
∠
G
K
C2
R2
Phase Boost
R3
G
C1
G
AMP
p
=
P
=
(f)
=
=
=
=
(f)
⎧
⎨
⎩
--------------------------------------------------------------- -
2 π
----------------------------------------------------------------------- -
2 π
------------------------------------------------- -
2 π
----------------- -
(
Tan
st
nd
rd
C2
=
K 1
=
×
×
×
R1
=
pole frequency =
pole frequency =
–
pole frequency =
20
------------------------------- -
G
tan
×
×
×
×
⎛
⎝
p
)
(
×
Boost
--------------- -
F
F
K 1
F
(F
–
BIAS
=
cross
log
cross
cross
1
1
4
–
K
⎛ ⎞
⎝ ⎠
cross
cross
M
--- -
f
1
f
z
M
)
–
1
⎞
⎠
to set the output voltage using EQ.5. Choose the zero crossover frequency F
0
×
×
×
–
∠
should be less than 1/5th of F
+
)
+
G
tan
C1
G
45
10
K
f
AMP
P
z
cross
–
×
(F
1
×
=
f
⎫
⎬
⎭
f
p1
f
R3
⎛
⎝
p3
2
p2
cross
log
------ -
f
×
----------------------------------------- -
2
p1
f
using EQ.30 by substituting F
R1
=
×
=
=
⎞
⎠
π C
--------------------------------------------------------------------------------------------------------- -
–
---------------------------------------------------------- -
2
)
------------------------- -
2 π
------------
2
1
×
–
ω
tan
×
×
+
1
×
2
n
90°
1
π
π
⎛
⎝
×
–
o
------ -
f
×
×
1
p1
×
f
×
L
⎛
⎝
⎛
⎝
R
⎛
⎝
e
⎞
⎠
------ -
f
R
C
p2
------------------- -
C
f
p
2
es
o
1
o
⎞
⎠
×
×
1
×
–
R
R
–
1
p
1
tan
L
+
+
+
+
sw
⎛
⎝
------ -
R
–
L
⎛ ⎞
⎝ ⎠
R
------ -
L
------ -
f
1
. Choose the desired phase margin. Typically this number should
--- -
f
e
p2
L
f
f
⎛
⎝
z
e
p
⎞
⎠
------ -
f
⎞
⎠
⎞
⎠
p3
2
f
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. 26)
(EQ. 27)
(EQ. 28)
(EQ. 29)
(EQ. 30)
(EQ. 31)
(EQ. 32)
(EQ. 33)
(EQ. 34)
(EQ. 35)
(EQ. 36)
(EQ. 37)
(EQ. 38)
(EQ. 39)