FAN5069 Fairchild Semiconductor, FAN5069 Datasheet - Page 16

• 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
FAN5069 has a high gain error amplifier around which
the loop is closed. Figure 24 shows a Type-3 compensa-
tion network. For Type-2 compensation, R3 and C3 are
not used. Since the FAN5069 architecture employs sum-
ming current mode, Type-2 compensation can be used
for most applications.
Type 3 Feedback Component Calculations
Use the following 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 =
Sampling gain quality factor (damping) =
Effective inductance =
G
L
R
R
R
T
R
C
F
V
s
L
SW
DSON
es
IN
p
0
p
=
s ( )
=
=
=
=
Inductor Value
=
=
=
Switching Period
Load Resistance
-------------------------------- -
M
Net Output Filter capacitance
M
=
Net ESR of the Output Filter Capacitors
Input Voltage
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
------ -
v
R
v
V
-------- -
V
R
n
L
×
+
+
i
IN
m
i
=
M
M
------------------- -
ω
×
M
=
n
i
i
Q
----- -
T
v
π
7
×
s
×
z
10
×
Q
R
=
R
z
×
i
⎞
⎠
–
----- -
DSON
(
---------------------------------------- -
π
2
V
IN
R
–
ramp
1.8
16
) T
×
For further information about Type-2 compensation
networks, refer to:
■
Note: For critical applications requiring wide loop
bandwidth using very low ESR output capacitors,
use Type-3 compensation.
s
Venable, H. Dean, "The K factor: A new mathematical
tool for stability analysis and synthesis,” Proceedings
of Powercon, March 1983.
www.fairchildsemi.com
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