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PDF ( 数据手册 , 数据表 ) NX2114

零件编号 NX2114
描述 300kHz & 600kHz SYNCHRONOUS PWM CONTROLLER
制造商 Microsemi
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NX2114 数据手册, 描述, 功能
Evaluation board available.
NX2114/2114A
300kHz & 600kHz SYNCHRONOUS PWM CONTROLLER
PRELIMINARY DATA SHEET
Pb Free Product
DESCRIPTION
FEATURES
The NX2114 controller IC is a synchronous Buck con- n Synchronous Controller in 8 Pin Package
troller IC designed for step down DC to DC converter n Bus voltage operation from 2V to 25V
applications. Synchronous control operation replaces n Single 5V Supply Operation
the traditional catch diode with an Nch MOSFET result- n Short protection with feedback UVLO
ing in improved converter efficiency.Although the NX2114 n Internal 300kHz for 2114 and 600kHz for 2114A
controller is optimized to convert single 5V bus voltages n Internal Digital Soft Start Function
to supplies as low as 0.8V output voltage, however us- n Shut Down via pulling comp pin low
ing a few external components it can also be used for n Pb-free and RoHS compliant
other input supplies such as 12V input (See NX2113
data sheet for more optimized solution). The NX2114
operates at 300kHz while 2114A is set at 600kHz n
operation which together with less than 50 nS of dead n
band provides an efficient and cost effective solution. n
Other features of the device are:
Internal digital soft start; Vcc undervoltage lock out; Out- n
put undervoltage protection with digital filter and shut- n
down capability via the enable pin.
APPLICATIONS
Graphic Card on board converters
Memory Vddq Supply in mother board applications
On board DC to DC such as
5V to 3.3V, 2.5V or 1.8V
Hard Disk Drive
Set Top Box
TYPICAL APPLICATION
L2 1uH
Vin
+5V C4
47uF,70mohm
R5
10 D1 MBR0530T1
OFF R6 10k
ON
R7
10k
C8
47uF,70mohm
2N3904
C1
47pF
C6
1uF
5
Vcc
7 Comp
C2
1.5nF
R4
22.1k
6
Fb
1
BST
Hdrv 2
SW 8
Ldrv 4
C7
0.1uF
Gnd
3
C5
1uF
M1
L1 1.5uH
M2
Cin
220uF,12mohm
Vout
+1.6V,6A
Co
2 x (220uF,15mohm)
R2
10.2k
R1 10.2k
R3 C3
1.5k 2.2nF
Device
NX2114CSTR
NX2114ACSTR
Figure1 - Typical application of 2114
ORDERING INFORMATION
Temperature
0 to 70oC
0 to 70o C
Package
SOIC-8L
SOIC-8L
Frequency
300kHz
600kHz
Pb-Free
Yes
Yes
Rev. 4.0
06/20/06
1







NX2114 pdf, 数据表
NX2114/2114A
APPLICATION INFORMATION
Symbol Used In Application Information:
VIN - Input voltage
VOUT - Output voltage
IOUT - Output current
DVRIPPLE - Output voltage ripple
FS - Working frequency
DIRIPPLE - Inductor current ripple
Design Example
The following is typical application for NX2114, the
schematic is figure 2.
VIN = 5V
VOUT=1.6V
IOUT=6A
DVRIPPLE <=20mV
DVDROOP<=60mV @ 6A step
Output Inductor Selection
The selection of inductor value is based on
inductor 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. Usually 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 application requirements. The inductor value
can be calculated by using the following equations:
LOUT
= VIN - VOUT
IRIPPLE
× VOUT
VIN
×1
FS
IRIPPLE = k ×IOUTPUT
where k is between 0.2 to 0.4.
Select k=0.4, then
...(1)
LOUT
=
5V-1.6V
0.4 × 6A
×
1.6V
5V
×
1
300kHz
LOUT =1.51uH
Choose inductor from COILCRAFT DO3316P-152
with L=1.5uH is a good choice.
Current Ripple is recalculated as
IRIPPLE
=
VIN -VOUT
LOUT
× VOUT
VIN
×1
FS
= 5V-1.6V × 1.6v × 1 = 2.4A
1.5uH 5v 300kHz
...(2)
Output Capacitor Selection
Output capacitor is basically decided by the
amount of the output voltage ripple allowed during steady
state(DC) load condition as well as specification for the
load transient. The optimum design may require a couple
of iterations to satisfy both condition.
Based on DC Load Condition
The amount of voltage ripple during the DC load
condition is determined by equation(3).
VRIPPLE
=
ESR × ∆IRIPPLE
+
IRIPPLE
8 × FS × COUT
...(3)
Where ESR is the output capacitors' equivalent
series resistance,COUT is the value of output capacitors.
Typically when large value capacitors are selected
such as Aluminum Electrolytic,POSCAP and OSCON
types are used, the amount of the output voltage ripple
is dominated by the first term in equation(3) and the
second term can be neglected.
For this example, POSCAP are chosen as output
capacitors, the ESR and inductor current typically de-
termines the output voltage ripple.
ESRdesire
=
VRIPPLE
IRIPPLE
=
20mV
2.3A
= 8.6m
...(4)
If low ESR is required, for most applications, mul-
tiple capacitors in parallel are better than a big capaci-
tor. For example, for 20mV output ripple, POSCAP
4TPE220MF with 15mare chosen.
N = E S R E × ∆ IR I P P L E
VRIPPLE
Number of Capacitor is calculated as
...(5)
N = 15mΩ × 2.3A
20mV
N =1.8
The number of capacitor has to be round up to a
integer. Choose N =2.
Rev. 4.0
06/20/06
8







NX2114 equivalent, schematic
cap which usually is 1uF need to be practically touch-
ing the drain pin of the upper MOSFET, a plane connec-
tion is a must.
3. The output capacitors should be placed as close
as to the load as possible and plane connection is re-
quired.
4. Drain of the low-side MOSFET and source of
the high-side MOSFET need to be connected thru a plane
ans as close as possible. A snubber nedds to be placed
as close to this junction as possible.
5. Source of the lower MOSFET needs to be con-
nected to the GND plane with multiple vias. One is not
enough. This is very important. The same applies to the
output capacitors and input capacitors.
6. Hdrv and Ldrv pins should be as close to
MOSFET gate as possible. The gate traces should be
wide and short. A place for gate drv resistors is needed
to fine tune noise if needed.
7. Vcc capacitor, BST capacitor or any other by-
passing capacitor needs to be placed first around the IC
and as close as possible. The capacitor on comp to
GND or comp back to FB needs to be place as close to
the pin as well as resistor divider.
8. The output sense line which is sensing output
back to the resistor divider should not go through high
frequency signals.
9. All GNDs need to go directly thru via to GND
plane.
10. The feedback part of the system should be
kept away from the inductor and other noise sources,
and be placed close to the IC.
11. In multilayer PCB, separate power ground and
analog ground. These two grounds must be connected
together on the PC board layout at a single point. The
goal is to localize the high current path to a separate
loop that does not interfere with the more sensitive ana-
log control function.
Rev. 4.0
06/20/06
NX2114/2114A
16










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