NCP3125CRAGEVB ON Semiconductor, NCP3125CRAGEVB Datasheet - Page 11

• Manufacturer Part Number: NCP3125CRAGEVB
• Description: BOARD EVALUATION NCP3125 CERAMIC
• Manufacturer: ON Semiconductor
• Series: -r

Specifications of NCP3125CRAGEVB

• Design Resources: NCP3125 Schematic NCP3125CRAGEVB BOM
• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Power - Output: -
• Voltage - Output: Adj down to 0.8V
• Current - Output: 4A
• Voltage - Input: 4.5 ~ 13.2 V
• Regulator Topology: Buck
• Frequency - Switching: 350kHz
• Board Type: Fully Populated
• Utilized Ic / Part: NCP3125
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: NCP3125CRAGEVBOS

I
DCR
LP
geometry of the selected core, core material, and wire used.
Most vendors will provide the appropriate information to
make accurate calculations of the power dissipation at which
point the total inductor losses can be captured by the
equation below:
LP
LP
LP
Output Capacitor Selection
output capacitor are DC voltage rating, ripple current rating,
output ripple voltage requirements, and transient response
requirements.
current at full load with proper derating. The RMS ratings
given in datasheets are generally for lower switching
frequency than used in switch mode power supplies, but a
multiplier is usually given for higher frequency operation.
The RMS current for the output capacitor can be calculated
below:
Co
I
ra
combination of the ripple current selected, the output
capacitance selected, the Equivalent Series Inductance
(ESL), and Equivalent Series Resistance (ESR).
to the ESR of the output capacitor and the capacitance
selected, which can be calculated as shown in Equation 14:
Co
C
F
I
ra
RMS
OUT
OUT
SW
LP
V
OUT
LP
The core losses and AC copper losses will depend on the
The important factors to consider when selecting an
The output capacitor must be rated to handle the ripple
The maximum allowable output voltage ripple is a
The main component of the ripple voltage is usually due
60.91 mV + 4 * 30% * 50 mW )
CU_DC
CU_DC
CU_AC
Core
RMS
ESR
ESR_C
Co
tot
_DC
RMS
+ LP
303 mW + 281 mW ) 1 mW ) 21 mW
+ I
+ I
281 mW + 4.01
+ I
RMS
CU_DC
OUT
= Inductor RMS current
= Inductor DC resistance
= Inductor DC power dissipation
= Inductor DC power dissipation
= Inductor AC power dissipation
= Inductor core power dissipation
= Output capacitor RMS current
= Output current
= Ripple current ratio
= Output capacitor ESR
= Output capacitance
= Switching frequency
= Output current
= Ripple current ratio
OUT
2
* ra * Co
@ DCR ³
@
) LP
ra
12
³ 0.346 A + 4 A
CU_AC
2
ESR
@ 17.5 mW
) LP
)
8 * F
8 * 350 kHz * 470 mF
Core
SW
1
³
* C
30%
12
OUT
1
(eq. 12)
(eq. 14)
(eq. 13)
(eq. 11)
³
http://onsemi.com
11
but tends to range from 1 nH to 20 nH, where ceramic
capacitors have the lowest inductance and electrolytic
capacitors have the highest. The calculated contributing
voltage ripple from ESL is shown for the switch on and
switch off below:
D
ESL
F
Ipp
response of the power supply. For the first few microseconds
of a load transient, the output capacitor supplies current to
the load. Once the regulator recognizes a load transient, it
adjusts the duty ratio, but the current slope is limited by the
inductor value.
drops due to the current variation inside the capacitor and the
ESR (neglecting the effect of the ESL).
Co
I
DV
current during the load transient without discharging it. The
voltage drop due to output capacitor discharge is given by
the following equation:
C
D
I
L
V
V
DV
of capacitor discharge
DV
TRAN
TRAN
SW
OUT
V
V
DV
OUT
MAX
IN
OUT
The ESL of capacitors depends on the technology chosen,
The output capacitor is a basic component for the fast
During a load step transient, the output voltage initially
A minimum capacitor value is required to sustain the
ESR
ESLON
ESLOFF
OUT_ESR
OUT_DIS
OUT*ESR
OUT*DIS
4.9 mV +
+
15.27 mV +
5.79 mV +
+
ESL * Ipp * F
+ I
ESL * Ipp * F
+
= Duty ratio
= Capacitor inductance
= Switching frequency
= Peak−to−peak current
= Output capacitor Equivalent Series
= Output transient current
= Voltage deviation of V
= Output capacitance
= Maximum duty ratio
= Output transient current
= Output inductor value
= Input voltage
= Output voltage
= Voltage deviation of V
TRAN
2
Resistance
effects of ESR
( 1 * D )
D
2
D
10 nH * 1.2 A * 350 kHz
MAX
10 nH * 1.2 A * 350 kHz
Co
75%
SW
I
SW
TRAN
C
ESR
1 * 27.5%
³
OUT
³
2.3 A
27.5%
³ 115 mV + 2.3
2
470 mF
L
2
V
OUT
OUT
IN
OUT
* V
5.6 mH
due to the effects
12 V * 3.3 V
due to the
OUT
³
(eq. 15)
(eq. 16)
(eq. 17)
(eq. 18)
50 mW