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PDF MP8709 Data sheet ( Hoja de datos )
| Número de pieza | MP8709 | |
| Descripción | Synchronous Step-down Converter | |
| Fabricantes | MPS | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de MP8709 (archivo pdf) en la parte inferior de esta página. Total 14 Páginas | ||
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The Future of Analog IC Technology
MP8709
High Efficiency 4A, 21V, 500kHz
Synchronous Step-down Converter
DESCRIPTION
The MP8709 is a high frequency synchronous
rectified step-down switch mode converter with
built in power MOSFETs. It offers a very
compact solution to achieve 4A continuous
output current over a wide input supply range
with excellent load and line regulation. The
MP8709 has synchronous mode operation for
higher efficiency over output current load range.
MP8709 achieves low EMI signature with well
controlled switching edges.
Current mode operation provides fast transient
response and eases loop stabilization.
Full protection features include OCP and
thermal shut down.
The MP8709 requires a minimum number of
readily available standard external components
and is available in a space saving 8-pin SOIC
package with an exposed pad.
FEATURES
• Wide 4.5V to 21V Operating Input Range
• 4A Output Current
• Low Rds(on) Internal Power MOSFETs
• Low-EMI Switching Speed Technology
• High Efficiency Synchronous Mode Operation
• Fixed 500kHz Switching Frequency
• Sync from 300kHz to 2MHz External Clock
• Internal Compensation
• Integrated Bootstrap Diode
• OCP Protection (Hiccup Mode)
• Thermal Shutdown
• Output Adjustable from 0.8V
• Available in a Thermally Enhanced 8-pin SOIC
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 “MPS”
and “The Future of Analog IC Technology” are Registered Trademarks of
Monolithic Power Systems, Inc.
TYPICAL APPLICATION
VIN
ON/OFF
21
1 IN
C1
22uF
7 VCC
C3
0.1uF
MP8709
5 EN/SYNC
GND
8
BST 4
SW 2,3
C4
0.1uF
L1
1.8uH
FB 6
Rt
56k
R1
4.99k
R2
10k
C2
47uF
VOUT 1.2V
Efficiency
VOUT=1.2V
100
90
VIN=4.5V
80
70
60
50 VIN=21V
VIN=12V
40
30
20
10
0
0 0.5 1 1.5 2 2.5 3 3.5
4
OUTPUT CURRENT (A)
MP8709 Rev. 1.01
www.MonolithicPower.com
12/14/2011
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
1
1 page  
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, VOUT = 1.2V, L=1.8μH, TA = +25ºC, unless otherwise noted.
Enabled Supply Current vs
Input Voltage
750
745
740
735
730
725
720
715
710
705
700
0 5 10 15 20 25
Disabled Supply Current vs
Input Voltage
0.2
0.15
0.1
0.05
0
-0.05
-0.1
-0.15
-0.2
0 5 10 15 20 25
Vcc Regulator Line Regulation
5.5
5
4.5
4
3.5
0
5 10 15 20 25
Peak Current vs
Duty Cycle
7
6.8
6.6
6.4
6.2
6
5.8
5.6
5.4
5.2
5
0 10 20 30 40 50 60 70 80 90100
Operating Range
100
Dmax Limit
10
1
0.1
0
Minimum on time Limit
5 10 15 20 25
Load Regulation
0.1
0.05
VIN=4.5V
0
-0.05
VIN=21V
VIN=12V
-0.1
-0.15
-0.2
01234
Line Regulation
0.2
0.15
0.1
0.05
0
-0.05
-0.1
-0.15
-0.2
0
Io=0A
Io=2A
Io=4A
5 10 15 20 25
.
Case Temperature Rise vs.
Output Current
50
40
30
20
10
0
012345
MP8709 Rev. 1.01
www.MonolithicPower.com
12/14/2011
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
5
5 Page 
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
APPLICATION INFORMATION
Setting the Output Voltage
The external resistor divider is used to set the
output voltage (see Typical Application on page
1). The feedback resistor R1 also sets the
feedback loop bandwidth with the internal
compensation capacitor (see Typical Application
on page 1). Choose R1 to be around 40.2kΩ for
optimal transient response. R2 is then given by:
R2 = R1
VOUT − 1
VFB
The T-type network is highly recommended when
Vo is low, as Figure 3 shows.
FB 1
Rt
R1
VOUT
R2
Figure 3— T-type Network
Table 1 lists the recommended T-type resistors
value for common output voltages.
Table 1—Resistor Selection for Common
Output Voltages
VOUT R1
(V) (kΩ)
R2
(kΩ)
Rt L
COUT
(kΩ) (μH) (μF, Ceramic)
1.05 4.99 16.5
56 1-4.7
47
1.2 4.99 10.2
56 1-4.7
47
1.5 4.99 5.76
47 1-4.7
47
1.8 4.99 4.02
47 1-4.7
47
2.5 10 4.75
30 1-4.7
47
3.3 10 3.24
20 1-4.7
47
5 10 1.91
15 1-4.7
47
Note:
The above feedback resistor table applies to a specific load
capacitor condition as shown in the table 1. Other capacitive loading
conditions will require different values.
Selecting the Inductor
A 1µH to 10µH inductor with a DC current rating
of at least 25% percent higher than the maximum
load current is recommended for most
applications. For highest efficiency, the inductor
DC resistance should be less than 15mΩ. For
most designs, the inductance value can be
derived from the following equation.
L
=
VOUT × (VIN − VOUT )
VIN × ΔIL × fOSC
Where ΔIL is the inductor ripple current.
Choose inductor ripple current to be
approximately 30% if the maximum load current,
4A. The maximum inductor peak current is:
IL(MAX)
= ILOAD
+
ΔIL
2
Under light load conditions below 100mA, larger
inductance is recommended for improved
efficiency.
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
⎟⎞
⎟
⎠
The worse case condition occurs at VIN = 2VOUT,
where:
IC1
=
ILOAD
2
For simplification, choose the input capacitor
whose RMS current rating greater than half of the
maximum load current.
The input capacitor can be electrolytic, tantalum
or ceramic. When electrolytic or tantalum
capacitors are used, a small, high quality ceramic
capacitor, i.e. 0.1μF, should be placed as close
to the IC as possible. When using ceramic
MP8709 Rev. 1.01
www.MonolithicPower.com
12/14/2011
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet MP8709.PDF ] | |
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