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NX2141 Schematic ( PDF Datasheet ) - Microsemi

Teilenummer NX2141
Beschreibung SINGLE CHANNEL MOBILE PWM CONTROLLER
Hersteller Microsemi
Logo Microsemi Logo 




Gesamt 21 Seiten
NX2141 Datasheet, Funktion
NX2141
SINGLE CHANNEL MOBILE PWM CONTROLLER WITH
FEEDFORWARD AND ENABLE
ADVANCE DATA SHEET
Pb Free Product
DESCRIPTION
FEATURES
The NX2141 controller IC is a compact synchronous Buck n Bus voltage operation from 7V to 24V
controller IC designed for step down DC to DC con- n Less than 1uA shutdown current with Enable low
verter applications with voltage feedforward functionality. n Excellent dynamic response with input voltage feed-
Voltage feedforward provides fast response, good line forward and voltage mode control
regulation and nearly constant power stage gain under n Internal Digital Soft Start Function
wide voltage input range. The NX2141 controller is opti- n Fixed internal hiccup current limit
mized to convert single supply up to 24V bus voltage to n FB UVLO followed by hiccup feature
as low as 0.8V output voltage. Internal UVLO keeps the n Power Good indicator available
regulator off until the supply voltage exceeds 7V where n Start into precharged output
internal digital soft starts get initiated to ramp up output. n Pb-free and RoHS compliant
The NX2141 employs fixed current limiting and FB UVLO
followed by hiccup feature. Other features includes: 5V
gate drive capability , Adaptive dead band control, avail- n
able in 16 lead MLPQ and 10 lead MSOP package. n
n
APPLICATIONS
Notebook PC
Graphic Card on board converters
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
Vin1
1uH
+8 to 20V
100uF
MBR0530T1
1uF
25TQC33M
25V,33uF
Vin2
+5V
1uF 13 8 16
10
1uF
PVCC VIN
14 VCC
BST
Hdrv 1
0.1uF
M1
10k
ON
OFF
5 PGOOD
9 EN
SW 15
12 COMP
2.3k
1nF
15nF
11 FB
Pgnd
2
Ldrv 3
Gnd
17
1uH
M2 1.5k
2.2nF
Vout
+1.05V 10A
Co
2*2R5TPE220MC
(220uF,12mohm)
10k
32k
Figure1 - Typical application of NX2141(MLPQ)
ORDERING INFORMATION
Device
NX2141CMTR
NX2141CUTR
Temperature
-40o C to 85o C
-40o C to 85o C
Package
MLPQ-16L
MSOP-10L
Frequency
200kHz
200kHz
Pb-Free
Yes
Yes
Rev. 1.6
05/15/07
1






NX2141 Datasheet, Funktion
NX2141
Vin1
+8 to 20V
100uF
Vin2
+5V
1nF
1uH
10
0.1uF
MBR0530T1
1uF 13 8 16
10
1uF
PVCC VIN
14 VCC
BST
Hdrv 1
0.1uF
10k 5 PGOOD
9 EN
12 COMP
2.3k
SW 15
Ldrv 3
15nF
11 FB
Pgnd
2
Gnd
17
1uF
M1
1uH
M2 1.5k
2.2nF
25TQC33M
25V,33uF
Vout
+1.05V 10A
Co
2*2R5TPE220MC
(220uF,12mohm)
10k
32k
Figure 3 - Simplified Demo board schematic(MLPQ)
Rev. 1.6
05/15/07
6

6 Page









NX2141 pdf, datenblatt
NX2141
If ceramic capacitors are chosen as output ca-
pacitors, both terms in equation (3) need to be evalu-
ated to determine the overall ripple. Usually when this
type of capacitors are selected, the amount of capaci-
tance per single unit is not sufficient to meet the tran-
sient specification, which results in parallel configura-
tion of multiple capacitors.
For example, two 100uF, X5R ceramic capacitor
with 2mESR is used. The amount of output ripple is
VRIPPLE
= 1mΩ× 4.97A +
4.97A
8× 200kHz× 200uF
= 5mV +15mV = 20mV
Two ceramic capacitors are needed. Although this
can meet DC ripple spec, however it needs to be stud-
ied for transient requirement.
Based On Transient Requirement
Typically, the output voltage droop during transient
is specified as
V droop < ∆V tran @step load DISTEP
During the transient, the voltage droop during the
transient is composed of two sections. One section is
dependent on the ESR of capacitor, the other section is
a function of the inductor, output capacitance as well
as input, output voltage. For example, for the over-
shoot when load from high load to light load with a
DISTEP transient load, if assuming the bandwidth of
system is high enough, the overshoot can be esti-
mated as the following equation.
Vovershoot
= ESR × ∆Istep
+
VOUT
2 × L × COUT
× τ2
...(6)
where τ is the a function of capacitor,etc.
τ
=
0
 L

if
× ∆Istep
VOUT
L
Lcrit
ESR ×
COUT
where
if L Lcrit
...(7)
Lcrit
=
ESR × COUT × VOUT
Istep
=
ESR E × CE × VOUT
Istep
...(8)
where ESRE and CE represents ESR and capaci-
tance of each capacitor if multiple capacitors are used
in parallel.
The above equation shows that if the selected out-
put inductor is smaller than the critical inductance, the
voltage droop or overshoot is only dependent on the ESR
of output capacitor. For low frequency capacitor such
as electrolytic capacitor, the product of ESR and ca-
pacitance is high and L Lcrit is true. In that case, the
transient spec is mostly like to dependent on the ESR
of capacitor.
Most case, the output capacitor is multiple capaci-
tor in parallel. The number of capacitor can be calcu-
lated by the following
N = ESR E × ∆Istep +
VOUT
× τ2
Vtran
2 × L × CE × ∆Vtran
where
...(9)
τ
=
0
 L

if
× ∆Istep
VOUT
L
Lcrit
ESR E
×
CE
if L Lcrit ...(10)
For example, assume voltage droop during tran-
sient is 50mV for 5A load step.
If the POSCAP 2R5TPE220MC(220uF, 12mohm
ESR) is used, the crticial inductance is given as
Lcrit
=
ESRE ×CE × VOUT
Istep
=
12mΩ×220µF×1.05V = 0.55µH
5A
The selected inductor is 1uH which is bigger than
critical inductance. In that case, the output voltage tran-
sient not only dependent on the ESR, but also capaci-
tance.
number of capacitor is
τ
=
L × ∆Istep
VOUT
ESR E
× CE
= 1µH × 5A 12mΩ × 220µF = 2.12us
1.05V
N = ESR E × ∆Istep +
VOUT
× τ2
Vtran
2 × L × CE × ∆Vtran
= 12mΩ × 5A +
1.05V
× (2.12us)2
53mV 2 ×1µH × 220µF × 53mV
= 1.35
Rev. 1.6
05/15/07
12

12 Page





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