NCP3127AGEVB ON Semiconductor, NCP3127AGEVB Datasheet - Page 18

• Manufacturer Part Number: NCP3127AGEVB
• Description: BOARD EVAL NCP3127
• Manufacturer: ON Semiconductor

Specifications of NCP3127AGEVB

• Design Resources: NCP3127AGEVB Schematic
• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Power - Output: -
• Voltage - Output: Adj down to 0.8V
• Current - Output: 2A
• Voltage - Input: 4.5 ~ 13.2 V
• Regulator Topology: Buck
• Frequency - Switching: 350kHz
• Board Type: Fully Populated
• Utilized Ic / Part: NCP3127A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

22 mF with a crossover frequency of 35 kHz, the
compensation values for common output voltages can be
calculated as shown in Table 6:
Calculating Soft−Start Time
following equations can be used.
C
C
I
a regulated output voltage is t
SS
Table 6. COMPENSATION VALUES
P
C
Assuming an output capacitance of 470 mF in parallel with
To calculate the soft−start delay and soft−start time, the
The time the output voltage takes to increase from 0 V to
V
(V)
12
12
12
12
12
12
12
12
12
t
t
5
5
5
5
5
5
5
in
SSdelay
SS
7.64 ms +
2.57 ms +
+
C
V
+
0.8
1.0
1.1
1.2
1.5
1.8
2.5
3.3
5.0
0.8
1.0
1.1
1.2
1.5
1.8
2.5
(V)
out
P
) C
= Compensation pole capacitor
= Compensation capacitor
= Soft−start current
C
P
1.28 nF ) 83.6 nF
1.28 nF ) 83.6 nF
) C
C
L
(mF)
10.0
12.0
15.0
10.0
4.7
4.7
4.7
6.8
6.8
8.2
4.7
4.7
5.6
5.6
6.8
8.2
I
out
SS
I
C
SS
D
10 mA
1000
1000
(nF)
0.9 V
390
390
330
330
270
220
390
390
330
330
270
220
Cf
V
NI
NI
ss
ramp
as shown in Equation 46:
10 mA
³
(nF)
150
150
150
120
120
120
120
100
100
150
150
150
150
150
150
150
Cc
0.9 V
27.5%
0.536
0.649
0.732
(kW)
1.27
1.82
2.87
3.16
4.02
1.27
1.62
1.91
2.15
2.74
4.42
5.36
1.1
Rc
1.1 V
(eq. 45)
(eq. 46)
http://onsemi.com
0.680
0.560
(nF)
0.82
0.68
0.56
0.39
3.3
2.7
2.7
1.5
1.5
1.2
1.0
1.5
1.2
1.0
Cp
18
C
C
D
I
t
V
to the bottom of the ramp is considered t
delay time is the addition of the current set delay and t
which in this case is 6 ms and 7.64 ms respectively, for a
total of 13.64 ms.
Calculating Input Inrush Current
charging and output charging. The input charging of a buck
stage is usually not controlled, and is limited only by the
input RC network, and the output impedance of the upstream
power stage. If the upstream power stage is a perfect voltage
source, then the input charge inrush current can be depicted
as shown in Figure 26 and calculated as:
SS
SS
P
C
ramp
The delay from the charging of the compensation network
The input inrush current has two distinct stages: input
Figure 26. Input Charge Inrush Current
Vcomp
Vout
I
ICinrush_PK
120 A +
IPK
= Compensation pole capacitor
= Compensation capacitor
= Duty ratio
= Soft−start interval
= Peak−to−peak voltage of the ramp
= Soft−start current
Figure 25. Soft−Start Ramp
1 +
0.1
12
CIN
V
V
IN
ESR
900 mV
ssdelay
. The total
(eq. 47)
ssdelay
,