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PDF NB634 Data sheet ( Hoja de datos )
| Número de pieza | NB634 | |
| Descripción | Synchronous Step-down Converter | |
| Fabricantes | MPS | |
| Logotipo |  |
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The Future of Analog IC Technology
DESCRIPTION
The NB634 is a high efficiency synchronous
rectified step-down switch mode converter with
built-in internal power MOSFETs. It offers a
very compact solution to achieve 5A continuous
output current over a wide input supply range
with excellent load and line regulation. The
NB634 operates at high efficiency over a wide
output current load range.
Current mode operation provides fast transient
response and eases loop stabilization.
Full protection features include latch-off OCP and
thermal shut down.
The NB634 requires a minimum number of
readily available standard external components
and is available in a space saving QFN14 (3mm x
4mm) package.
NB634
High Efficiency 5A, 24V, 500kHz
Synchronous Step-down Converter
FEATURES
Wide 4.5V to 24V Operating Input Range
5A Output Current
Low RDS(ON) Internal Power MOSFETs
Proprietary Switching Loss Reduction
Technique
Fixed 500kHz Switching Frequency
Sync from 300kHz to 2MHz External Clock
Internal Compensation
Latch-off OCP Protection and Thermal
Shutdown
Output Adjustable from 0.8V
Available in a QFN14 (3mmx4mm) Package
APPLICATIONS
Notebook Systems and I/O Power
Networking Systems
Digital Set Top Boxes
Personal Video Recorders
Flat Panel Television and Monitors
Distributed Power Systems
All MPS parts are lead-free and adhere to the RoHS directive. For MPS green
status, please visit MPS website under Products, Quality Assurance page.
“MPS” and “The Future of Analog IC Technology” are registered trademarks of
Monolithic Power Systems, Inc.
TYPICAL APPLICATION （FOR NOTEBOOK）
4.5V-24V
VIN
VCC
C1
22uF
R3
R4
ON/OFF
1 IN
3.3V
9
PG
10 AAM
11
C3
VCC
0.1uF
NB634
7 EN/SY NC
BST 6
SW 2,3,4,5
C4
0.1uF
L1
2.3uH
8
FB
Rt
24.9k
GND
12,13,14
R1
10k
R2
8.06k
C2
47uF
VOUT 1.8V
Efficiency
VOUT=1.8V, L=1.0uH
100
95 VIN=7V
90
VIN=12V
85
80 VIN=24V
75
70
65
60
55
50
012345
OUTPUT CURRENT (A)
6
NB634 Rev. 0.94
12/25/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
1
1 page  
NB634 –HIGH EFFICIENCY, 5A, 24V, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS
VIN=12V, VOUT =1.8V, L=1.0µH, TA=+25°C, unless otherwise noted.
Quiescent Current vs.
Input Voltage
590
Shutdown Current vs.
Input Voltage
0.1
585
580 0.05
575
570 0
565
560 -0.05
555
550
0
VFB=1V
5 10 15 20
INPUT VOLTAGE (V)
25
-0.1
0
5 10 15 20
INPUT VOLTAGE (V)
25
VCC Regulator Line Regulation
5.5
5.0
4.5
4.0
3.5
0
IOUT=0A
5 10 15 20
INPUT VOLTAGE (V)
25
Peak Current vs.
Duty Cycle
10
9
8
7
6
5
4
3
2
1
0
0 20 40 60 80
DUTY CYCLE(%)
100
Line Regulation
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
0
IO=2.5A
IO=5A
5 10 15 20
INPUT VOLTAGE (V)
25
Operating Range
100
Dmax Limit
10
1 Minimun on time Limit
0.1
0
5 10 15 20
INPUT VOLTAGE (V)
25
Case Temperature Rise
vs. Output Current
50
40
30
20
10
0
012345
OUTPUT CURRENT (A)
6
Load Regulation
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
0
VIN=7V
VIN=24V
VIN=12V
12345
OUTPUT CURRENT (A)
6
Efficiency
VOUT=1.8V, L=1.0uH
100
95 VIN=7V
90
VIN=12V
85
80 VIN=24V
75
70
65
60
55
50
012345
OUTPUT CURRENT (A)
6
NB634 Rev. 0.94
12/25/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
5
5 Page 
NB634 –HIGH EFFICIENCY, 5A, 24V, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER
1.0
0.9 VO=3.3V
0.8 VO=5V
0.7 VO=1.8V
0.6
0.5
0.4
0.3
0.2 VO=1.05V
0.1
0.0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Figure 5— AAM Selection for Common
Output Voltages (VIN=7V-24V)
Selecting the Input Capacitor
The input current to the step-down converter is
discontinuous, therefore a capacitor is required to
supply the AC current to the step-down converter
while maintaining the DC input voltage. Use low ESR
capacitors for the best performance. Ceramic
capacitors with X5R or X7R dielectrics are highly
recommended because of their low ESR and
small temperature coefficients. For most
applications, a 22µF capacitor is sufficient.
Since the input capacitor (C1) absorbs the input
switching current, it requires an adequate ripple
current rating. The RMS current in the input capacitor
can be estimated by:
IC1 ILOAD
VOUT
VIN
1
VOUT
VIN
(5)
The worst case condition occurs at VIN = 2VOUT,
where:
IC1
ILOAD
2
(6)
For simplification, choose the input capacitor
whose RMS current rating is greater than half of
the maximum load current.
The input capacitor can be electrolytic, tantalum
or ceramic. When using electrolytic or tantalum
capacitors, a small, high quality ceramic
capacitor, i.e. 0.1μF, should be placed as close
to the IC as possible. When using ceramic
capacitors, make sure that they have enough
capacitance to provide sufficient charge to
prevent excessive voltage ripple at input. The
input voltage ripple caused by capacitance can
be estimated by:
VIN
ILOAD
fSW C1
VOUT
VIN
1
VOUT
VIN
(7)
Selecting the Output Capacitor
The output capacitor (C2) is required to maintain
the DC output voltage. Ceramic, tantalum, or low
ESR electrolytic capacitors are recommended.
Low ESR capacitors are preferred to keep the
output voltage ripple low. The output voltage
ripple can be estimated by:
VOUT
VOUT
fSW L1
1
VOUT
VIN
RESR
1
8
fSW
C2
(8)
Where L1 is the inductor value and RESR is the
equivalent series resistance (ESR) value of the
output capacitor.
In the case of ceramic capacitors, the impedance
at the switching frequency is dominated by the
capacitance. The output voltage ripple is mainly
caused by the capacitance. For simplification, the
output voltage ripple can be estimated by:
ΔVOUT
8
VOUT
fSW 2 L1
C2
1
VOUT
VIN
(9)
In the case of tantalum or electrolytic capacitors,
the ESR dominates the impedance at the
switching frequency. For simplification, the output
ripple can be approximated to:
ΔVOUT
VOUT
fSW L1
1
VOUT
VIN
RESR
(10)
The characteristics of the output capacitor also
affect the stability of the regulation system. The
NB634 can be optimized for a wide range of
capacitance and ESR values.
NB634 Rev. 0.94
12/25/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet NB634.PDF ] | |
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