ncp3101c ON Semiconductor, ncp3101c Datasheet - Page 18

• Manufacturer Part Number: ncp3101c
• Description: Ncp3101c Wide Input Voltage Synchronous Buck Converter
• Manufacturer: ON Semiconductor

determining phase margin. To start the design, a resistor
value should be chosen for R
components can be chosen. A good starting value is 10 kW.
regulator to be adjusted down to 0.8 V via an external
resistor divider network. The regulator will maintain 0.8 V
at the feedback pin. Thus, if a resistor divider circuit was
placed across the feedback pin to V
regulate the output voltage proportional to the resistor
divider network in order to maintain 0.8 V at the FB pin.
above and the output voltage is shown in Equation 39:
R
R
V
V
The most frequently used output voltages and their
associated standard R
1
2
OUT
REF
The NCP3101C allows the output of the DC−DC
The relationship between the resistor divider network
Figure 30. Feedback Resistor Divider
= Top resistor divider
= Bottom resistor divider
= Output voltage
= Regulator reference voltage
R
2
+ R
1
1
and R
@
V
2
OUT
values are listed in Table 6.
V
2
REF
* V
from which all other
OUT
REF
, the regulator will
(eq. 39)
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18
Transconductance Error Amplifier can be calculated using
the method described below. The method serves to provide
a good starting place for compensation of a power supply.
The values can be adjusted in real time using the
compensation tool comp calc, available for download at
ON Semiconductor’s website.
follows if RF is reduced to zero.
The first pole is set at the ESR zero.
The second pole is set at zero crossover frequency.
The first zero should be set at the LC pole frequency.
The second zero is determined automatically by F
Table 6. OUTPUT VOLTAGE SETTINGS
The compensation components for the Pseudo Type III
The poles of the compensation network are calculated as
V
O
0.8
1.0
1.1
1.2
1.5
1.8
2.5
3.3
5.0
(V)
F
F
P2
F
F
P1
z1
z2
+
+
R
+
+
2p @
1
2.55
3.83
4.99
12.7
21.5
31.6
52.3
1.0
10
2p @ R
2p @ R
2p @ R
(kW)
R
R
1
1
)R
1
1
1
1
@R
C
C
1
2
@ C
@ C
@ C
2
@ C
C
F
P
F
R
Open
2
10.2
10.2
11.5
10
10
10
10
10
(kW)
P2
(eq. 40)
(eq. 41)
(eq. 42)
(eq. 43)
.