FAN8060 Fairchild Semiconductor, FAN8060 Datasheet - Page 10

• Manufacturer Part Number: FAN8060
• Description: The FAN8060 is a highly efficient, monolithic, currentmode, step-down synchronous regulator
• Manufacturer: Fairchild Semiconductor

© 2008 Fairchild Semiconductor Corporation
FAN8060 • Rev. 1.0.0
The system pole is calculated by the equation:
The system zero is due to the output capacitor and its
ESR. System zero is calculated by the equation:
The output characteristics of the error (Gm) amplifier
are controlled by a series capacitor and resistor
network connected at the COMP pin to GND.
The pole is calculated by the following equation:
where:
G
and
C
Zero is due to the compensation capacitor (C
resistor (R
where R
The system crossover frequency (f
loop has unity gain, is recommended to be set at 1/10
of switching frequency. Generally, higher f
faster response to load transients, but can result in
instability if not properly compensated.
The first step in compensation design is choosing the
compensation resistor (R
frequency by the following equation:
where V
The next step is choosing the compensation capacitor
(C
applications with typical inductor values, setting the
compensation zero, f
crossover frequency provides sufficient phase margin.
Determine the (C
Then determine if the second compensation capacitor
(C
output capacitor is located at less than half of the
switching frequency.
C
f
f
f
f
R
2
P
z
p
z
C
EA
π
1
C
C
1
2
2
C
A
) is required. It is required if the ESR zero of the
=
) to achieve the desired phase margin. For
=
⋅
=
=
=
=
= Error Amplifier Transconductance (1000µA/V);
= compensation capacitor.
C
2
2
π
2
OUT
2
2
π
π
π
π
π
⋅
1
⋅
⋅
R
G
FB
⋅
C
C
C
⋅
⋅
2
C
C
C
CS
G
C
⋅
is compensation resistor.
OUT
OUT
C
C
is reference voltage.
ESR
1
1
OUT
⋅
EA
C
1
) calculated by the following equation:
f
C
⋅
⋅
⋅
A
G
⋅
⋅
R
VEA
R
ESR
EA
⋅
<
C
f
L
C
f
C
⋅
2
S
V
⋅
) value by the following equation:
V
FB
OUT
Z2
, to below one fourth of the
C
) to set the crossover
C
), where the control
C
means
C
) and
(10)
(11)
(12)
(13)
(7)
(8)
(9)
th
10
If required, add the second compensation capacitor
(C
Determine (C
Design Example
Table 2 provides component values for delivering
various output voltages with loads up to 1A with V
5V (+/-10% tolerance).
Table 2. Recommended Feedback and
Compensation Values (V
1.2V
1.5V
1.8V
2.5V
3.3V
Figure 15. Recommended Schematic (5V
C
V
A
A
O
) to set the pole f
=
C
10µF 3.3µH
OUT
C
4
R
C
⋅
ESR
A
L
) value by the equation:
1
2.55kΩ 10.2kΩ
16.2kΩ
18.7kΩ 10.7kΩ
5.9kΩ
Short
P3
R
2
at the location of the ESR zero.
IN
11.8kΩ
=5V)
Open
15kΩ
R
3
4.7kΩ 1.5nF 150pF
R
1
www.fairchildsemi.com
IN
C
5
to 2.5V
(14)
C
IN
2
O
at
)