nx2116 Microsemi Corporation, nx2116 Datasheet - Page 6

• Manufacturer Part Number: nx2116
• Description: Synchronous Pwm Controller With Current Limit, Power Good & Over Voltage
• Manufacturer: Microsemi Corporation

APPLICATION INFORMATION
Symbol Used In Application Information:
Design Example
the schematic is figure 1.
Output Inductor Selection
tor 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. Usu-
ally 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 appli-
cation requirements. The inductor value can be calcu-
lated by using the following equations:
102HC with L=1uH is a good choice.
Rev. 3.0
03/14/06
DI
I
DV
F
F
I
DV
DV
V
V
V
V
OUT
OUT
S
S
IN
IN
OUT
OUT
RIPPLE
=600kHz
The following is typical application for NX2116A,
RIPPLE
RIPPLE
DROOP
= 12V
=9A
=1.8V
The selection of inductor value is based on induc-
where k is between 0.2 to 0.4.
Select k=0.3, then
Choose inductor from COILCRAFT DO3316P-
Current Ripple is recalculated as
I
L
L
L
RIPPLE
OUT
OUT
OUT
<=100mV @ 9A step
<=20mV
- Working frequency
- Inductor current ripple
- Output voltage ripple
- Output current
- Input voltage
- Output voltage
=
=0.94uH
=
=k I
12V-1.8V 1.8V
V -V
0.3 9A
IN
I
RIPPLE
OUTPUT
OUT
V
12V
V
OUT
IN
600kHz
F
1
S
1
...(1)
NX2116/2116A/2116B/2117/2117A
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
2R5TPE220MC with 12m are chosen.
integer. Choose N =2.
I
RIPPLE
ESR
N
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 =1.5
The number of capacitor has to be round up to a
If ceramic capacitors are chosen as output ca
N
V
=
=
RIPPLE
12m
desire
V -V
12V-1.8V 1.8v
IN
E S R
L
1uH
OUT
=
20mV
OUT
ESR
V
I
2.56A
RIPPLE
E
RIPPLE
V
OUT
R I P P L E
V
V
12V 600kHz
OUT
IN
is the value of output capacitors.
I
I
R I P P L E
RIPPLE
2.55A
20mV
F
1
S
1
8 F
7.8m
I
S
RIPPLE
2.55A
C
OUT
.
...(2)
...(3)
...(4)
..(5)
6