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PDF NCV8925 Data sheet ( Hoja de datos )
| Número de pieza | NCV8925 | |
| Descripción | 600mA Step-Down DC-DC Converter | |
| Fabricantes | ON Semiconductor | |
| Logotipo |  |
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NCV8925
3 MHz, 600 mA Step-Down
DC-DC Converter
High-Efficiency, Low Ripple, Adjustable
Output Voltage
The NCV8925 DC-DC buck converter is available in a space saving
low profile TSOP-5 and mUDFN6 package. The part can supply output
voltages from 0.9 V to 3.3 V by an external resistor divider and is able
to deliver output currents up to 600 mA. This switching regulator
operates at 3.0 MHz and automatically switches between PFM and
PWM modes to improve system efficiency.
Soft-start, cycle-by-cycle current limiting and thermal shutdown
protection are also integrated in NCV8925.
The device is optimized for automotive applications and bring a high
frequency DC-DC solution for automotive requirements.
Features
•ăUp to 93% Efficiency
•ăAllow Use of Small External Components
•ăSource up to 600 mA
•ă3 MHz Switching Frequency
•ăAdjustable Output Voltage from 0.9 V to 3.3 V
•ăSynchronous Rectification for Higher Efficiency
•ă2.7 V to 5.5 V Input Voltage Range
•ăLow Quiescent Current
•ăShutdown Current Consumption of 0.3 mA
•ăThermal Limit Protection
•ăShort Circuit Protection
•ăAll Pins are Fully ESD Protected
•ăThese are Pb-Free Devices
•ăNCV Prefix for Automotive and Other Applications Requiring Site
and Control Changes
http://onsemi.com
UDFN6
MU SUFFIX
CASE 517AB
MARKING
DIAGRAMS
16
2 ZEG 5
3 G4
5
1
TSOP-5
SN SUFFIX
CASE 483
5
ACNAYWG
G
1
ZE,ACN= Specific Device Code
A = Assembly Location
Y = Year
W = Work Week
G = Pb-Free Package
(Note: Microdot may be in either location)
ORDERING INFORMATION
Device
Package
Shipping†
NCV8925MUTBG UDFN6 3000/Tape & Reel
(Pb-Free)
NCV8925SNT1G
TSOP-5 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 LX 5
2 GND
3 EN
FB 4
L
COUT
VOUT
R1
R2
Figure 1. Typical Application - TSOP-5
OFF ON
Cff
1 EN FB 6
2 GND LX 5
3 VIN GND 4
R2
L R1
Cff
VOUT
COUT
CIN
VIN
Figure 2. Typical Application - UDFN6
©Ă Semiconductor Components Industries, LLC, 2008
April, 2008 - Rev. 0
1
Publication Order Number:
NCV8925/D
1 page  
NCV8925
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
6
7
8, 9
10, 11, 12
13
14
15
16, 17
18, 19
20, 21
22, 23, 25, 25
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN, INPUT VOLTAGE (V)
Figure 6. Shutdown Current vs. Supply Voltage
56
54
52
50
48
46
44
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN, INPUT VOLTAGE (V)
Figure 7. Quiescent Current PFM No Switching
vs. Supply Voltage
http://onsemi.com
5
5 Page 
NCV8925
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 a 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 NCV8925, a low profile 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 AUTOMOTIVE CAPACITORS
Murata
GCM31CR71C475
4.7 mF
TDK
C3216X7R1E475MT
4.7 mF
Output L-C Filter Design Considerations
The NCV8925 operates at 3 MHz frequency and uses
voltage 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 NCV8925, the internal compensation is internally
fixed and it is optimized for an output filter of L = 2.2 mH
and COUT = 4.7 mF.
The corner frequency is given by:
fc + 2p ǸL
1
COUT
+
2p
1
Ǹ2.2ĂmH
+ 49ĂkHz
4.7ĂmF
(eq. 3)
The device is intended to operate with inductance value
of 2.2 mH.
If the corner frequency is moved, it is recommended to
check the loop stability depending on the accepted output
ripple voltage and the required output curret. 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
2.2 mH
Output Capacitor (COUT)
10 mF
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 performance, the DC
resistance should be less than 0.3 W for good efficiency.
Table 3. LIST OF AUTOMOTIVE INDUCTORS
Coilcraft
DO3316T-102ML
DO3316T-222ML
1.0 mH
2.2 mH
TDK
NLCV32T-1R0M-PF
NLCV32T-2R2M-PF
1.0 mH
2.2 mH
11 A
7.8 A
1.0 A
0.77 A
http://onsemi.com
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| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet NCV8925.PDF ] | |
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