nx2116 Microsemi Corporation, nx2116 Datasheet - Page 12

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

at 75% of the LC double pole.
at half the swithing frequency.
Output Voltage Calculation
ternal voltage divider. The reference voltage is fixed at
0.8V. The divider consists of two ratioed resistors so
that the output voltage applied at the Fb pin is 0.8V when
the output voltage is at the desired value. The following
equation and picture show the relationship between
of R
Rev. 3.0
03/14/06
V
OUT
1
R =
value can be set by voltage divider.
4.Calculate R
Choose R
5. Calculate C
Choose C
6. Calculate C
Choose C
Output voltage is set by reference voltage and ex-
where R
See compensator design for R
C =
R =
3
C =
,
=
=8.15k
V
1
1
1.5V
2
12V
=
=8.9nF
REF
V
=
= 1 2 9 p F
V
2
OSC
2
in
V
R
and voltage divider. .
O U T
1.8V
0.8V
2
2
is part of the compensator, and the value
2
1
1
2
=120pF.
3
=8.2nF.
R
1
8 . 2 k
R
8.2k
=8.2k
1
-V
V
3
3
3
R
1
2
R E F
value by the following equation.
R E F
by setting compensator pole
by setting compensator zero F
ESR
F
6.5m
60kHz 1uH
F
F
z
O
s
1
1
0.75 2.9kHz
L
3 0 0 k H z
g
1
m
...(18)
V
V
1
OUT
REF
2.0mA/V
and R
1
2
selection.
NX2116/2116A/2116B/2117/2117A
F
p
Z
Input Capacitor Selection
ceramic capacitors and bulk capacitors. Ceramic ca-
pacitors bypass the high frequency noise, and bulk ca-
pacitors supply switching current to the MOSFETs. Usu-
ally 1uF ceramic capacitor is chosen to decouple the
high frequency noise.The bulk input capacitors are de-
cided by voltage rating and RMS current rating. The RMS
current in the input capacitors can be calculated as:
the result of input RMS current is 3.2A.
ommended. One Sanyo OS-CON 16SP180M 16V 180uF
20m
capacitors.
Power MOSFETs Selection
MOSFETs. The selection of MOSFETs is based on
maximum drain source voltage, gate source voltage,
maximum current rating, MOSFET on resistance and
power dissipation. The main consideration is the power
loss contribution of MOSFETs to the overall converter
efficiency. In this design example, two IRFR3709Z are
used. They have the following parameters: V
=6.5m ,Q
loss:conduction loss, switching loss.
V
IN
Input capacitors are usually a mix of high frequency
For higher efficiency, low ESR capacitors are rec-
The power stage requires two N-Channel power
Conduction loss is simply defined as:
I
D
There are two factors causing the MOSFET power
R2
R1
RMS
= 12V, V
with 3.4A RMS rating is chosen as input bulk
Vout
Figure 8 - Voltage divider
GATE
V
Voltage divider
V
OUT
I
OUT
IN
Vref
=17nC.
OUT
Fb
=1.8V, I
D
1- D
OUT
=9A, using equation (19),
...(19)
DS
=30V,R
DSON
12