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PDF NCP1521B Data sheet ( Hoja de datos )
| Número de pieza | NCP1521B | |
| Descripción | Step-Down DC-DC Converter | |
| Fabricantes | ON Semiconductor | |
| Logotipo |  |
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NCP1521B
1.5 MHz, 600 mA
Step−Down DC−DC
Converter
High−Efficiency, Low Ripple, Adjustable
Output Voltage
The NCP1521B step−down PWM DC−DC converter is optimized
for portable applications powered from one cell Li−ion or three cell
Alkaline/NiCd/NiMH batteries. The part is available in adjustable
output voltage versions ranging from 0.9 V to 3.3 V. It uses
synchronous rectification to increase efficiency and reduce external
part count. The device also has a built−in 1.5 MHz (nominal)
oscillator which reduces component size by allowing smaller
inductors and capacitors. Automatic switching PWM/PFM mode
offers improved system efficiency.
Additional features include integrated soft−start, cycle−by−cycle
current limiting and thermal shutdown protection. The NCP1521B is
available in space saving, low profile TSOP5 and UDFN6 packages.
Features
• Up to 96% Efficiency
• Best−In−Class Ripple, including PFM Mode
• Sources up to 600 mA
• 1.5 MHz Switching Frequency
• Adjustable Output Voltage from 0.9 V to 3.3 V www.DataSheet4U.com
• Synchronous Rectification for Higher Efficiency
• 2.7 V to 5.5 V Input Voltage Range
• Low Quiescent Current
• Shutdown Current Consumption of 0.3 mA
• Thermal Limit Protection
• Short Circuit Protection
• All Pins are Fully ESD Protected
• This is a Pb−Free Device
Typical Applications
• Cellular Phones, Smart Phones and PDAs
• Digital Still/Video Cameras
• MP3 Players and Portable Audio Systems
• Wireless and DSL Modems
• Portable Equipment
• USB Powered Devices
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MARKING
DIAGRAM
5
1
TSOP−5
SN SUFFIX
CASE 483
5
DBPAYWG
G
1
DBP = Specific Device Code
A = Assembly Location
Y = Year
W = Work Week
G = Pb−Free Package
(Note: Microdot may be in either location)
UDFN6
MU SUFFIX
CASE 517AB
1
2
ZCMG
6
5
3G4
ZC = Specific Device Code
M = Date Code
G = Pb−Free Package
(Note: Microdot may be in either location)
ORDERING INFORMATION
Device
NCP1521BSNT1G
NCP1521BMUTBG
Package
Shipping†
TSOP−5 3000/Tape & Reel
(Pb−Free)
UDFN6 3000/Tape & Reel
(Pb−Free)
†For information on tape and reel specifications,
including part orientation and tape sizes, please
refer to our Tape and Reel Packaging Specification
Brochure, BRD8011/D.
VIN
CIN
OFF ON
1 VIN
2 GND
3 EN
LX 5
FB 4
L
COUT
Figure 1. Typical Application − TSOP−5
VOUT
R1
R2
OFF ON
Cff
1 EN FB 6
2 GND LX 5
R2
2.2 mH R1
3 VIN GND 4
18 pF
VOUT
10 mF
4.7 mF
VIN
Figure 2. Typical Application − UDFN6
© Semiconductor Components Industries, LLC, 2007
March, 2007 − Rev. 0
1
Publication Order Number:
NCP1521B/D
1 page  
NCP1521B
TABLE OF GRAPHS
Typical Characteristics for Step−down Converter
ISTB
Iq
VOUT
Eff
Standby Current
Quiescent Current, PFM No Switching
Output Voltage Accuracy
Efficiency
vs. Input Voltage
vs. Input Voltage
vs. Temperature
vs. Output Current
Freq
Switching Frequency
vs. Input Voltage
VOUT
VOUT
VOUT
VOUT
VOUT
VOUT
Soft−Start
Short Circuit Protection
Line Regulation
Line Transient
Load Regulation
Load Transient
vs. Time
vs. Time
vs. Input Voltage
vs. Time
vs. Output Current
vs. Time
Figure
7
8
9 and 10
11, 12, and 13
14
15
16
17 and 18
19, 20, 21, and 22
23 and 24
25, 26, 27, and 28
1.0
0.9 EN = 0 V
0.8 IOUT = 0 mA
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2.7 3.2 3.7 4.2 4.7 5.2
VIN, INPUT VOLTAGE (V)
Figure 7. Shutdown Current vs. Supply Voltage
35
EN = VIN
34 IOUT = 0 mA
33
32
31
30
29
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN, INPUT VOLTAGE (V)
Figure 8. Quiescent Current PFM No Switching
vs. Supply Voltage
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5
5 Page 
NCP1521B
APPLICATION INFORMATION
Output Voltage Selection
The output voltage is programmed through an external
resistor divider connected from VOUT to FB then to GND.
For low power consumption and noise immunity, the
resistor from FB to GND (R2) should be in the
[100 k−600 k] range. If R2 is 200 k given the VFB is 0.6 V,
the current through the divider will be 3.0 mA.
The formula below gives the value of VOUT, given the
desired R1 and the R1 value:
VOUT + VFB (1 ) RR12)
• VOUT: Output Voltage (Volts)
• VFB: Feedback Voltage = 0.6 V
• R1: Feedback Resistor from VOUT to FB
• R2: Feedback Resistor from FB to GND
(eq. 2)
Input Capacitor Selection
In PWM operating mode, the input current is pulsating
with large switching noise. Using an input bypass capacitor
can reduce the peak current transients drawn from the
input supply source, thereby reducing switching noise
significantly. The capacitance needed for the input bypass
capacitor depends on the source impedance of the input
supply.
The maximum RMS current occurs at 50% duty cycle
with maximum output current, which is Iout_max/2.
For NCP1521B, a low profile, low ESR ceramic
capacitor of 4.7 mF should be used for most of the cases. For
effective bypass results, the input capacitor should be
placed as close as possible to the VIN pin.
Table 1. List of Input Capacitor
Murata
GRM188R60J475KE
GRM21BR71C475KA
Taiyo Yuden
JMK212BY475MG
TDK
C2012X5ROJ475KB
C1632X5ROJ475KT
Output L−C Filter Design Considerations
The NCP1521B operates at 1.5 MHz frequency and uses
current mode architecture. The correct selection of the
output filter ensures good stability and fast transient
response.
Due to the nature of the buck converter, the output L−C
filter must be selected to work with internal compensation.
For NCP1521B, the internal compensation is internally
fixed and it is optimized for an output filter of L = 2.2 mH
and COUT = 10 mF.
The corner frequency is given by:
fc + 2p ǸL
1
COUT
+
2p
Ǹ2.2
1
mH
+ 34 kHz
10 mF
(eq. 3)
The device is intended to operate with inductance values
between 1.0 mH and maximum of 4.7 mH.
If the corner frequency is moved, it is recommended to
check the loop stability depending on the output ripple
voltage accepted and output current required. For lower
frequency, the stability will be increased; a larger output
capacitor value could be chosen without critical effect on
the system. On the other hand, a smaller capacitor value
increases the corner frequency and it should be critical for
the system stability. Take care to check the loop stability.
The phase margin is usually higher than 45°.
Table 2. L−C Filter Example
Inductance (L)
1.0 mH
Output Capacitor (Cout)
22 mF
2.2 mH
10 mF
4.7 mH
4.7 mF
Inductor Selection
The inductor parameters directly related to device
performances are saturation current and DC resistance and
inductance value. The inductor ripple current (DIL)
decreases with higher inductance:
ǒ ǓDIL
+
VOUT
L fSW
1−
VOUT
VIN
(eq. 4)
DIL peak to peak inductor ripple current
L inductor value
fSW switching frequency
The saturation current of the inductor should be rated
higher than the maximum load current plus half the ripple
current:
IL(MAX)
+
IO(MAX)
)
DIL
2
(eq. 5)
DIL(MAX) Maximum inductor current
DIO(MAX) Maximum Output current
The inductor’s resistance will factor into the overall
efficiency of the converter. For best performances, the DC
resistance should be less than 0.3 W for good efficiency.
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11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet NCP1521B.PDF ] | |
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