NCP3170ADR2G ON Semiconductor, NCP3170ADR2G Datasheet - Page 21

• Manufacturer Part Number: NCP3170ADR2G
• Description: IC BUCK SYNC/ASYNC ADJ 3A 8SOIC
• Manufacturer: ON Semiconductor
• Series: -r
• Type: Step-Down (Buck), PWM - Current Moder

Specifications of NCP3170ADR2G

• Internal Switch(s): Yes
• Synchronous Rectifier: Both
• Number Of Outputs: 1
• Voltage - Output: 0.8 V ~ 12.8 V
• Current - Output: 3A
• Frequency - Switching: 500kHz
• Voltage - Input: 4.5 V ~ 18 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

amplifier.
amplifier and the impedance networks Z
and external Z
network has to provide a closed loop transfer function with
the highest 0dB crossing frequency to have fast response and
the highest gain in DC conditions, so as to minimize load
regulation issues. A stable control loop has a gain crossing
with −20 dB/decade slope and a phase margin greater than
45°. Include worst−case component variations when
determining phase margin. To start the design, a resistor
value should be chosen for R
components can be chosen. A good starting value is 24.9 kW.
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
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 40:
Figure 45. Pseudo Type III Transconductance Error
Figure 45 shows a pseudo Type III transconductance error
The compensation network consists of the internal error
The NCP3170 allows the output of the DC−DC regulator
The relationship between the resistor divider network
RC
CC
ZFB
Figure 46. Feedback Resistor Divider
CP
FB
R
2
OUT
+ R
(R
, the regulator will regulate the output
C
, C
1
Amplifier
Gm
C
, and C
V
IEA
OUT
VREF
V
1
REF
* V
ZIN
from which all other
P
). The compensation
REF
IN
(R
R 1
R 2
1
, R
2
, and C
(eq. 40)
http://onsemi.com
CF
F
)
21
R
R
V
V
associated standard R
below.
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
http://www.onsemi.com/pub/Collateral/COMPCALC.ZIP
be setup at FPO to decrease at −20dB per decade:
F
F
G
used to calculate the transconductance output compensation
network as follows:
C
F
cross
PO
PO
1
2
OUTPUT VOLTAGE SETTINGS
C
OUT
REF
The most frequently used output voltages and their
The compensation components for the Pseudo Type III
The first pole to crossover at the desired frequency should
The crossover combined compensation network can be
V
O
0.8
1.0
1.1
1.2
1.5
1.8
2.5
3.3
5.0
(V)
= Top resistor divider
= Bottom resistor divider
= Output voltage
= Regulator reference voltage
= Cross over frequency
= Pole frequency to meet crossover
= DC gain of the plant
= Compensation capacitor
= Pole frequency
15.4 nF +
1.99 kHz +
frequency
C
F
C
1
PO
+
and R
R
+
2
2p
0.242
1
24.9
24.9
24.9
24.9
24.9
24.9
24.9
24.9
24.9
(kW)
F
50 kHz
y
42.65
CROSS
p
tool
2
1.994 kHz
G
values are listed in the table
gm
F
200 ms
³
PO
³
*³
R
Open
2
66.5
49.9
28.7
8.06
4.64
11.8
100
20
(kW)
CompCalc
(eq. 41)
(eq. 42)