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PDF ( 数据手册 , 数据表 ) NX2307

零件编号 NX2307
描述 SINGLE SUPPLY 12V SYNCHRONOUS PWM CONTROLLER
制造商 Microsemi
LOGO Microsemi LOGO 


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NX2307 数据手册, 描述, 功能
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







NX2307 pdf, 数据表
Demoboard waveforms
NX2307
Figure 4 - Output ripple for power output
Figure 5 - Output voltage transient response for
load current 0A-5A
Figure 6 - Start up time
Figure 7 - Prebias startup
Figure 8 - Shutdown via pulling comp pin down
Rev. 3.2
06/22/06
Figure 9 - Short circuit protection
8







NX2307 equivalent, schematic
NX2307
FESR
=
1
2 × π × ESR × COUT
=1
2 × π × 20.5mΩ ×1360uF
= 5.7kHz
2.Set R2 equal to10k. Using equation 18, the fi-
nal
selection
of
R
1
is
4.7kΩ.
3. Set crossover frequency at 1/10~ 1/5 of the
swithing frequency, here FO=30kHz.
4.Calculate R value by the following equation.
3
R3
=
VOSC
Vin
×
2 × π × FO
RESR
×L
×
1
gm
×
VOUT
VREF
=1.1V × 2 × π × 30kHz × 2.2uH × 1
12
20.5m
2mA/V
× 2.5V
0.8V
=2.9k
Choose R3 =2.87k.
5. Calculate C1 by setting compensator zero FZ
at 75% of the LC double pole.
C1=
2
×
π
1
× R3
×
Fz
=1
2 × π × 2.87kΩ × 0.75 × 2.9kHz
=25nF
Choose C1=27nF.
6. Calculate C2 by setting compensator pole Fp
at half the swithing frequency.
C2=
π
×
1
R3
×
Fs
=1
π × 2.87kΩ × 150kH z
=369pF
Choose C2=390pF.
Output Voltage Calculation
Output voltage is set by reference voltage and ex-
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 applies to figure 17, which shows the relation-
ship between VOUT , VREF and voltage divider.
Vout
R2
Fb
R1
Vref
Figure 16 - Voltage divider
R1=
R2 ×
VOUT
VREF
-VREF
...(21)
where R2 is part of the compensator, and the value
of R1 value can be set by voltage divider.
Input Capacitor Selection
Input capacitors are usually a mix of high frequency
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:
IRMS = IOUT × D × 1- D
D = VOUT
VIN
...(22)
VIN = 12V, VOUT=1.8V, IOUT=10A, the result of input
RMS current is 3.6A.
For higher efficiency, low ESR capacitors are
recommended. One Sanyo OS-CON 16SVP180M 16V
180uF 20mwith 3.64A RMS rating are chosen as
input bulk capacitors.
Rev. 3.2
06/22/06
16










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