nx2114 Microsemi Corporation, nx2114 Datasheet - Page 13

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

at 75% of the LC double pole.
at 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
Rev. 4.0
06/20/06
R =
Choose R
5. Calculate C
Choose C
6. Calculate C
Choose C
Output voltage is set by reference voltage and
where R
Choose R
C =
C =
R =
3
=
=4.23k
1
2
1.7V 2
1
=
=13.3nF
=
=235pF
V
12
V
V
1
2
OSC
2
p R
p 3.74k
in
value can be set by voltage divider.
OUT
V
R
10.2k +3.24k
O U T
2
2
1
2
,
1
2
3
is part of the compensator, and the
2
1
=12nF.
=220pF.
3
R
V
=10k , to set the output voltage at
4.51k
3.24k
=4.53k
-V
REF
3
V
F
R
s
1
2
R E F
1
ESR
R E F
F
30kHz 1.5uH
by setting compensator zero F
by setting compensator pole
and voltage divider. .
F
20.5
z
O
300kHz
1
L
0.75 3.5kHz
g
1
m
R +R
...(18)
1
R
1.9mA/V
1
2
1
F
Z
p
1.6V, the result of R
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,
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 2.80A.
ommended. One Sanyo TPD series POSCAP 6TPD220M
6V 220uF with 12m is chosen as input bulk capacitor.
I
D
V
RMS
In general, the minimum output load impedance
Vout=1.6V
The power loss is 1/16W less
Select minimum load, 1k should be good enough.
Input capacitors are usually a mix of high frequency
For higher efficiency, low ESR capacitors are rec-
R
IN
R2
R1
LOAD
= 5V, V
Vout
V
Figure 13 - Voltage divider
V
OUT
I
IN
OUT
Voltage divider
1.6V 1.6V /(1/16W)
Vref
OUT
Fb
D
=1.6V, I
1
is 10k .
1- D
OUT
NX2114/2114A
=6A, using equation
40
...(19)
13