FAN5099 Fairchild Semiconductor, FAN5099 Datasheet - Page 16

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

FAN5099 Rev. 1.0.1
© 2006 Fairchild Semiconductor Corporation
FAN5099 has a high gain error amplifier around which
the loop is closed. Figure 25 shows a type 3 compensa-
tion network. For type 2 compensation, R3 and C3 are
not used. Since the FAN5099 architecture employs sum-
ming current mode, type 2 compensation can be used
for most applications. For for further information about
type 2 compensation networks, refer to the following :
■
Type 3 Feedback Component Calculations
Use these steps to calculate feedback components:
Notation:
Equations:
Effective current sense resistance =
Current modulator DC gain =
Effective ramp amplitude =
Voltage modulator DC gain =
Plant DC gain =
Sampling gain natural frequency =
Effective inductance =
R
R
T
V
R
C
G
L
R
F
s
i
SW
DSON
es
p
0
L
p
Venable, H. Dean, "The K factor: A new mathematical
tool for stability analysis and synthesis," Proceedings
of Powercon, March 1983.
=
s ( )
=
=
=
=
=
=
Inductor Value
Input Voltage
=
Switching Period
-------------------------------- -
M
net Output Filter Capacitance
Load Resistance
M
=
Net ESR of the output filter capacitors
Switching Frequency
v
v
=
Net Gain of Plant = control-to-output transfer function
×
×
On-State Drain-to Source Resistance of Low-side MOSFET
R
R
i
i
×
+
R
R
M
L
L
o
=
=
(
L
M
M
e
v
v
=
×
||
V
M
R
M
--------
M
m
M
M
i
i
O
v
) R
i
v
=
=
||
×
=
=
------------------- -
M
M
3.33 10
⎛
⎝
ω
L
L
R
------ -
R
------- -
V
R
v
v
V
n
L
+
i
m
×
+
i
i
=
------------------- -
ω
=
×
M
M
M
n
----- -
T
v
i
i
7 R
π
×
s
×
×
10
Q
R
z
i
×
⎞
⎠
DSON
(
------------------------------------ -
V
i
–
R
1.8
ramp
) T
16
×
Note: For critical applications requiring wide loop band-
width using very low ESR output capacitors, use type 3
compensation.
s
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