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PDF NX2307 Data sheet ( Hoja de datos )
| Número de pieza | NX2307 | |
| Descripción | SINGLE SUPPLY 12V SYNCHRONOUS PWM CONTROLLER | |
| Fabricantes | Microsemi | |
| Logotipo |  |
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NX2307
SINGLE SUPPLY 12V SYNCHRONOUS PWM CONTROLLER
ADVANCE DATA SHEET
Pb Free Product
DESCRIPTION
FEATURES
The NX2307 controller IC is a compact synchronous Buck
controller IC with 8 lead SOIC8 package designed for
step down DC to DC converter applications. The NX2307
n
n
n
12V Gate Driver
Bus voltage operation from 7V to 15V
Fixed hiccup current limit by sensing Rdson of
controller is optimized to convert single supply 12V bus
voltage to as low as 0.8V output voltage. Internal UVLO
n
Synchronous MOSFET
Internal 300kHz
keeps the regulator off until the supply voltage exceeds n Internal Digital Soft Start Function
7V where internal digital soft starts get initiated to ramp n Adaptive deadband Control
up output. The NX2307 employs fixed current limiting n Shut Down via pulling COMP pin
followed by HICCUP feature. Other features includes: n Pb-free and RoHS compliant
12V gate drive capability , Converter Shutdown by pull-
ing COMP pin to Gnd, Adaptive dead band control.
APPLICATIONS
n Graphic Card on board converters
n Vddq Supply in mother board applications
n On board DC to DC such as
12V to 3.3V, 2.5V or 1.8V
n Set Top Box and LCD Display
TYPICAL APPLICATION
Vin
+12V
M3
HI=SD
C7
200pF
L2 1uH
C4
100uF
R6
10
C3
1uF 5
Vcc
R4
5.36k
7 COMP
D1 MBR0530T1
1
BST
Hdrv 2
SW 8
C6
0.1uF
C2
6.8nF
6 FB
Ldrv 4
Gnd
3
C5
1uF
M1
IRFR3706
L1 1.5uH
R1
M2 1.43k
IRFR3706
C1
2.7nF
Cin
16SVP180M
16V,180uF
Vout
+1.8V 10A
Co
4SEPC560M
560uF,7mohm
R2
10k
R3
8k
Device
NX2307CSTR
Figure1 - Typical application of NX2307
ORDERING INFORMATION
Temperature
0 to 70oC
Package
SOIC - 8L
Frequency
300kHz
Pb-Free
Yes
Rev. 3.2
06/22/06
1
1 page  
BLOCK DIAGRAM
NX2307
VCC
Bias
Regulator
FB
COMP
Bias
Generator
1.25V
0.8V
6.6/6.3V
UVLO
COMP
0.2V
START 0.8V
Digital
start Up
OSC
ramp
POR
OC
SQ
R
START
PWM
Control
Logic
VCC
OC
START
0.6V
CLAMP
1.3V
CLAMP
Hiccup Logic
OCP
comparator
240mV
BST
HDRV
SW
LDRV
GND
Figure 2 - Simplified block diagram of the NX2307
Rev. 3.2
06/22/06
5
5 Page 
NX2307
The number of capacitors has to satisfied both ripple
and transient requirement. Overall, we choose N=1.
It should be considered that the proposed equa-
tion is based on ideal case, in reality, the droop or over-
shoot is typically more than the calculation. The equa-
tion gives a good start. For more margin, more capaci-
tors have to be chosen after the test. Typically, for high
frequency capacitor such as high quality POSCAP es-
pecially ceramic capacitor, 20% to 100% (for ceramic)
more capacitors have to be chosen since the ESR of
capacitors is so low that the PCB parasitic can affect
the results tremendously. More capacitors have to be
selected to compensate these parasitic parameters.
Compensator Design
Due to the double pole generated by LC filter of the
power stage, the power system has 180o phase shift ,
and therefore, is unstable by itself. In order to achieve
accurate output voltage and fast transient response,
compensator is employed to provide highest possible
bandwidth and enough phase margin. Ideally, the Bode
plot of the closed loop system has crossover frequency
between 1/10 and 1/5 of the switching frequency, phase
margin greater than 50o and the gain crossing 0dB with -
20dB/decade. Power stage output capacitors usually
decide the compensator type. If electrolytic capacitors
are chosen as output capacitors, type II compensator
can be used to compensate the system, because the
zero caused by output capacitor ESR is lower than cross-
over frequency. Otherwise type III compensator should
be chosen.
FZ1
=
1
2 × π ×R4
× C2
FZ2
=
1
2 × π × (R2 + R3 ) × C3
FP1
=
1
2 × π × R3
× C3
FP2
=
1
2
×
π
×
R4
×
C1
C1
×
+
C2
C2
...(11)
...(12)
...(13)
...(14)
where FZ1,FZ2,FP1 and FP2 are poles and zeros in
the compensator.
The transfer function of type III compensator for
transconductance amplifier is given by:
Ve =
1 − gm × Zf
VOUT 1 + gm × Zin + Zin / R1
For the voltage amplifier, the transfer function of
compensator is
Ve = −Zf
VOUT
Zin
To achieve the same effect as voltage amplifier, the
compensator of transconductance amplifier must sat-
isfy this condition: R4>>2/gm. And it would be desir-
able if R1||R2||R3>>1/gm can be met at the same time.
Vout
Zin
R3
R2
Zf
C1
C2 R4
A. Type III compensator design
For low ESR output capacitors, typically such as
Sanyo oscap and poscap, the frequency of ESR zero
caused by output capacitors is higher than the cross-
over frequency. In this case, it is necessary to compen-
sate the system with type III compensator. The follow-
ing figures and equations show how to realize the type III
compensator by transconductance amplifier.
C3 Fb
gm Ve
R1
Vref
Figure 10 - Type III compensator using
transconductance amplifier(C1 can also be
connected from comp pin to ground)
Rev. 3.2
06/22/06
11
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet NX2307.PDF ] | |
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