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PDF ( 数据手册 , 数据表 ) NX2415

零件编号 NX2415
描述 TWO PHASE SYNCHRONOUS PWM CONTROLLER
制造商 NEXSEM
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NX2415 数据手册, 描述, 功能
NEXSEM
Evaluation board available.
NX2415
TWO PHASE SYNCHRONOUS PWM CONTROLLER WITH
INTEGRATED FET DRIVER AND DIFFERENTIAL CURRENT SENSE
PRELIMINARY DATA SHEET
Pb Free Product
DESCRIPTION
FEATURES
The NX2415 is a two-phase PWM controller with inte- n Differential inductor DCR sensing eliminates the
grated FET driver designed for low voltage high current
application. The two phase synchronous buck converter
offers ripple cancelation for both input and output. The
NX2415 uses differential remote sensing using either
current sense resistor or inductor DCR sensing to achieve
accurate current matching between the two channels.
n
n
n
n
n
problem with layout parasitic
External programmable voltage droop
Low Impedance On-board Drivers
Hiccup current limit
Power Good for power sequencing
Enable Signal allows external shutdown as well as
Differential sensing eliminates the error caused by PCB
board trace resistance that is otherwise is present when
using a single ended voltage sensing. In addition the
NX2415 offers high drive current capability especially for
n
n
n
programming the BUS voltage start up threshold
Programmable frequency
Prebias start up
Over voltage protection without negative spike at
keeping the synchronous MOSFET off during SW node output
transition, accurate programmable droop allowing to re- n Pb-free and RoHS compliant
duce number of output capacitors, accurate enable cir-
APPLICATIONS
cuit provides programmable start up point for Bus volt- n Graphic card High Current Vcore Supply
age, PGOOD output, programmable switching frequencyn High Current +40A on board DC to DC converter
and hiccup current limiting circuitry.
applications
TYPICAL APPLICATION
+5V
10 31
VCC
1uF
10k 30
EN
+12V
6.49k
1.65k
29 ENBUS
+5V
op
45.3k
10k
7 DROOP
2 RT
28 PGOOD
VOUT
11 CSCOMP
430 220nF
1.8nF 3.92k
10k
2N3906
20k
2.2nF
10k
20k
5.62k
3 PGSEN
1nF
5 FB
6.8nF
6 VCOMP
150pF
PVCC1 23 1uF
+5V
1uH
BST1 24
HDRV1 25
SW1 26
2 x 10uF
180uF
0.22uF M1
2.15 0.68uH
LDRV1 22
M2 620
1uF
100uF
VIN1
+12V
VOUT
+1.2V/50A
2 x (1000uF,7mohm ESR)
PGND1 21
CS+1 9
CS-1 10
PVCC2 18
1uF
+5V
620
17
BST2
16
HDRV2
15
SW2
19
LDRV2
0.22uF
2.15
10uF
M3
0.68uH
M4 620
1uF
1k
180k
10nF
100k
4
8
VP
OCP
1 VREF
10nF
20
PGND2
CS+2 12
CS-2 13
1nF 14 IOUT AGND
32
620
Figure1 - Typical application of NX2415
ORDERING INFORMATION
Device
NX2415CMTR
Temperature
0 to 70oC
Package
MLPQ-32L
Frequency
200kHz to 1MHz
Pb-Free
Yes
Rev.4.8
05/06/08
www.nexsem.com
1
Free Datasheet http://www.Datasheet4U.com







NX2415 pdf, 数据表
NEXSEM
APPLICATION INFORMATION
Symbol Used In Application Information:
VIN - Input voltage
VOUT - Output voltage
IOUT - Output current
DVRIPPLE - Output voltage ripple
FS - Operation frequency for each channel
DIRIPPLE - Inductor current ripple
NX2415
LOUT =0.54uH
Choose inductor from Vishay IHLP_5050FD-01
with L=0.68uH DCR=1.4m.
Current Ripple is recalculated as
IRIPPLE
=
VIN -VOUT
LOUT
× VOUT
VIN
×1
FS
=12V-1.2V × 1.2V × 1 = 3.97A
0.68uH 12V 400kHz
...(2)
Design Example
The following is typical application for NX2415.
VIN = 12V
VOUT=1.2V
IOUT=50A
IOUT_max=60A
DVRIPPLE <=12mV
DVDROOP<=120mV @30A step
FS=400kHz
Phase number N=2
Output Inductor Selection
The selection of inductor value is based on induc-
tor ripple current, power rating, working frequency and
efficiency. Larger inductor value normally means smaller
ripple current. However if the inductance is chosen too
large, it brings slow response and lower efficiency. Usu-
ally the ripple current ranges from 20% to 40% of the
output current. This is a design freedom which can be
decided by design engineer according to various appli-
cation requirements. The inductor value can be calcu-
lated by using the following equations:
LOUT
=
VIN -VOUT
IRIPPLE
× VOUT
VIN
×1
FS
IRIPPLE
=k
×
IOUTPUT
N
where k is between 0.2 to 0.4.
Select k=0.2, then
...(1)
12V-1.2V
LOUT = 0.2 × 50A
×
1.2V
12V
×
1
400kHz
2
Output Capacitor Selection
Output capacitor value is basically decided by the
output voltage ripple, capacitor RMS current rating and
load transient.
Based on Voltage Ripple
For electrolytic, POSCAP bulk capacitor, the ESR
(equivalent series resistance) and inductor current typi-
cally determines the output voltage ripple.
ESRdesire
=
VRIPPLE
IRIPPLE
=
12mV
3.97A
= 3.022m
...(3)
If low ESR is required, for most applications, mul-
tiple capacitors in parallel are better than a big capaci-
tor. For example, for 12mV output ripple, SANYO OS-
CON capacitors 2R5SEPC1000MX(1000uF 7mΩ) are
chosen.
N = E S R E × ∆ IR I P P L E
VRIPPLE
Number of Capacitor is calculated as
...(4)
N = 7mΩ × 3.97A
12mV
N =2.3
For ceramic capacitor, the current ripple is deter-
mined by the number of capacitor instead of ESR
COUT
=
IRIPPLE
8 × FS × ∆VRIPPLE
...(5)
Typically, the calculated capacitance is so small
that the output voltage droop during the transient can
not meet the spec although ripple is small.
Rev.4.8
05/06/08
www.nexsem.com
8
Free Datasheet http://www.Datasheet4U.com







NX2415 equivalent, schematic
NEXSEM
NX2415
C2
=
1
π × Rcc
× FS
=
1
π × 430Ω × 400kHz
= 1.85nF
Select C2=2.2nF.
VREF
100k
OCP
Frequency Selection
The frequency can be set by external Rt resistor.
The relationship between frequency per phase and RT
pin is shown as follows.
RT
18600000
FS
...(20)
800
700
600
500
400
300
200
100
0
0
FREQUENCY(kHz) vs RT(kohm )
50 100 150
Rt(kohm )
200
ROCP
Figure 12 - Over current protection
Output Voltage Droop Operation
The effective output impedance of the controller must
be adjusted to maximize the output voltage fluctuation
range. A program resistor attached to the Droop pin
RDROOP will program this value. The function works by an
internal current source connected to the FB pin. This
current flows output of the FB pin and through the Rin
resistance from the FB pin to the output.
This current source is a function of the sensed
output current. As the output current increases, the droop
current will increase and causes the output voltage
todroop proportionately. The droop current is programmed
by a resistor attached to the Droop pin. The value of the
resistor is chosen as follows.
Figure 11 - Frequency vs Rt chart
Over Current/Short Circuit Protection
The converter will go into hiccup mode if the
output current reaches a programmed limit VOCP
determined by the voltage at pin OCP.
VOCP
=
0.6 60k
2kΩ +RS
DCR
2 IOCP
ROCP
=
VOCP
VREF VOCP
× 100k
...(21)
Where Iocp is the desired over current protection
level,100kis the resistor connecting VREF pin and
IOCP pin. RS is the current sensing matching resistor
when using DCR sensing method.
VOUT
RIN
FB
IDROOP
COMP
VP Error Amplifer
Figure 13 - Output voltage droop funciton
VOUT = IDROOP × RIN = ∆ILOAD × RLL
...(22)
Where R is desired load impedance. For example,
LL
if we want Vout droops 60mV @ 20A,
RLL
=
60mV
20A
=
3m
IDROOP
=
V(IOUT)
RDROOP
=
0.6 ×
60k
2kΩ + RS
×
DCR
2
× ILOAD
RDROOP
...(23)
Rev.4.8
05/06/08
www.nexsem.com
16
Free Datasheet http://www.Datasheet4U.com










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