nx2114 Microsemi Corporation, nx2114 Datasheet - Page 8

• Manufacturer Part Number: nx2114
• Description: 300khz & 600khz Synchronous Pwm Controller
• Manufacturer: Microsemi Corporation

APPLICATION INFORMATION
Symbol Used In Application Information:
Design Example
schematic is figure 2.
Output Inductor Selection
inductor ripple current, power rating, working frequency
and efficiency. Larger inductor value normally means
smaller ripple current. However if the inductance is
chosen too large, it brings slow response and lower
efficiency. Usually the ripple current ranges from 20%
to 40% of the output current. This is a design freedom
which can be decided by design engineer according to
various application requirements. The inductor value
can be calculated by using the following equations:
with L=1.5uH is a good choice.
Rev. 4.0
06/20/06
DV
DI
DV
I
F
V
I
DV
V
V
V
OUT
OUT
S
IN
IN
OUT
OUT
RIPPLE
The following is typical application for NX2114, the
RIPPLE
RIPPLE
DROOP
= 5V
=6A
=1.6V
The selection of inductor value is based on
where k is between 0.2 to 0.4.
Select k=0.4, then
Choose inductor from COILCRAFT DO3316P-152
Current Ripple is recalculated as
L
I
L
L
RIPPLE
OUT
OUT
OUT
<=20mV
<=60mV @ 6A step
- Working frequency
- Inductor current ripple
- Output voltage ripple
- Output current
- Input voltage
- Output voltage
=
=1.51uH
5V-1.6V 1.6V
0.4 6A
V - V
k I
IN
I
RIPPLE
OUTPUT
OUT
V
5V
V
OUT
IN
300kHz
F
1
S
1
...(1)
Output Capacitor Selection
amount of the output voltage ripple allowed during steady
state(DC) load condition as well as specification for the
load transient. The optimum design may require a couple
of iterations to satisfy both condition.
Based on DC Load Condition
condition is determined by equation(3).
series resistance,C
such as Aluminum Electrolytic,POSCAP and OSCON
types are used, the amount of the output voltage ripple
is dominated by the first term in equation(3) and the
second term can be neglected.
capacitors, the ESR and inductor current typically de-
termines the output voltage ripple.
tiple capacitors in parallel are better than a big capaci-
tor. For example, for 20mV output ripple, POSCAP
4TPE220MF with 15m are chosen.
integer. Choose N =2.
I
RIPPLE
ESR
Output capacitor is basically decided by the
The amount of voltage ripple during the DC load
Where ESR is the output capacitors' equivalent
Typically when large value capacitors are selected
For this example, POSCAP are chosen as output
If low ESR is required, for most applications, mul-
Number of Capacitor is calculated as
N
N =1.8
The number of capacitor has to be round up to a
N
V
=
RIPPLE
=
desire
15m
V -V
5V-1.6V 1.6v
E S R
IN
1.5uH
L
20mV
=
OUT
OUT
ESR
V
I
RIPPLE
E
RIPPLE
V
2.3A
OUT
R I P P L E
V
5v
V
OUT
is the value of output capacitors.
I
IN
I
R I P P L E
RIPPLE
20mV
2.3A
NX2114/2114A
300kHz
F
1
S
1
8 F
8.6m
I
S
RIPPLE
2.4A
C
OUT
.
...(2)
...(3)
...(4)
..(5)
8