nx2113 Microsemi Corporation, nx2113 Datasheet - Page 14

• Manufacturer Part Number: nx2113
• Description: 300khz & 600khz Synchronous Pwm Controller With Programmable Bus Uvlo
• Manufacturer: Microsemi Corporation

at 75% of the LC double pole.
half the swithing frequency.
Output Voltage Calculation
external 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
value of R
1.6V, the result of R
Rev. 2.0
11/18/05
6. Calculate C
5. Calculate C
Choose C
Choose C
Output voltage is set by reference voltage and
wher e R
Choose R
C =
R =
C =
R2
R1
1
1
Vout
2
=
=10.7nF
Figure 13 - Voltage divider load
V
=
= 1 0 6 p F
1
2
2
value can be set by voltage divider.
OUT
Voltage divider
V
R
O U T
2
2
Vref
,
1
2
is part of the compensator, and the
Fb
2
=10nF.
=100pF.
V
=10k , to set the output voltage at
1
R
1 0 k
R
10k
-V
REF
V
2
1
3
3
by setting compensator pole
1
R E F
1
R E F
by setting compensator zero F
is 10k .
and voltage divider. .
F
F
z
1
s
1
0.75 6.5kHz
3 0 0 k H z
...(18)
F
p
Z
at
including the resistor divider should be less than 5k to
prevent overcharge the output voltage by leakage cur-
rent (e.g. Error Amplifier feedback pin bias current). A
minimum load for 5k less (<1/16w for most of applica-
tion) is recommended to put at the output. For example,
in this application,
enough.
Input Capacitor Selection
ceramic capacitors and bulk capacitors. Ceramic ca-
pacitors bypass the high frequency noise, and bulk ca-
pacitors supply current to the MOSFETs. Usually 1uF
ceramic capacitor is chosen to decouple the high fre-
quency noise. The bulk input capacitors are decided by
voltage rating and RMS current rating. The RMS current
in the input capacitors can be calculated as:
(19), the result of input RMS current is 3.4A.
recommended. One Sanyo OSCON SP series
16SP270M 16V 270uF with 4.4A is chosen as input
bulk capacitor.
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 IRFR3706 are
used. They have the following parameters: V
=75A,R
I
D
V
RMS
In general, the minimum output load impedance
Vout=1.6V
The power loss is 1/16W less
Select minimum load is 1k
Input capacitors are usually a mix of high frequency
For higher efficiency, low ESR capacitors are
The NX2113 requires two N-Channel power
R
IN
LOAD
DSON
= 12V, V
V
V
OUT
I
IN
OUT
=9m ,Q
1.6V 1.6V /(1/16W)
OUT
D
=1.6V, I
GATE
1- D
=23nC.
NX2113/2113A
OUT
=10A, using equation
40
should be good
DS
=30V, I
...(19)
14
D