MP8709EN-LF [MPS]
Switching Regulator, Current-mode, 7.4A, 500kHz Switching Freq-Max, PDSO8, ROHS COMPLIANT, MS-012BA, SOIC-8;
| 型号： | MP8709EN-LF |
| 厂家： | 
MONOLITHIC POWER SYSTEMS |
| 描述： | Switching Regulator, Current-mode, 7.4A, 500kHz Switching Freq-Max, PDSO8, ROHS COMPLIANT, MS-012BA, SOIC-8 开关 光电二极管 输出元件 |
| 文件： | 总14页 (文件大小：414K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MP8709
High Efficiency 4A, 21V, 500kHz
Synchronous Step-down Converter
The Future of Analog IC Technology
DESCRIPTION
FEATURES
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.
•
•
•
•
•
•
•
•
•
•
•
•
•
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
MP8709 achieves low EMI signature with well
controlled switching edges.
Current mode operation provides fast transient
response and eases loop stabilization.
Output Adjustable from 0.8V
Available in a Thermally Enhanced 8-pin SOIC
package
Full protection features include OCP and
thermal shut down.
APPLICATIONS
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.
•
•
•
•
•
•
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
Efficiency
VOUT=1.2V
100
V
=4.5V
IN
90
80
70
60
50
40
30
20
10
0
21
1
4
VIN
IN
BST
C1
22uF
C4
0.1uF
V
=12V
IN
L1
1.8uH
V
=21V
2,3
IN
VOUT 1.2V
SW
FB
7
5
MP8709
VCC
R1
4.99k
C3
0.1uF
C2
47uF
6
Rt
56k
R2
10k
ON/OFF
EN/SYNC
GND
8
0
0.5
1
1.5
2
2.5
3
3.5
4
OUTPUT CURRENT (A)
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
1
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
ORDERING INFORMATION
Part Number*
Package
Top Marking
Free Air Temperature (TA)
MP8709EN
SOIC8E
MP8709EN
-20°C to +85°C
* For Tape & Reel, add suffix –Z (e.g. MP8709EN–Z);
For RoHS compliant packaging, add suffix –LF (e.g. MP8709EN–LF–Z)
PACKAGE REFERENCE
TOP VIEW
IN
SW
1
2
3
4
8
7
6
5
GND
VCC
SW
FB
BST
EN/SYNC
EXPOSED PAD
ON BACKSIDE
CONNECT TO GND
Thermal Resistance (4)
SOIC8E (Exposed Pad)..........50 ...... 10...°C/W
θJA
θJC
ABSOLUTE MAXIMUM RATINGS (1)
Supply Voltage VIN ....................................... 22V
V
V
SW........................-0.3V (-5V for < 10ns) to 23V
BS .......................................................VSW + 6V
Notes:
1) Exceeding these ratings may damage the device.
2) The maximum allowable power dissipation is a function of the
maximum junction temperature TJ(MAX), the junction-to-
ambient thermal resistance θJA, and the ambient temperature
TA. The maximum allowable continuous power dissipation at
any ambient temperature is calculated by PD(MAX)=(TJ(MAX)-
TA)/θJA. Exceeding the maximum allowable power dissipation
will cause excessive die temperature, and the regulator will go
into thermal shutdown. Internal thermal shutdown circuitry
protects the device from permanent damage.
All Other Pins..................................-0.3V to +6V
Operating Temperature.............. -20°C to +85°C
Continuous Power Dissipation (TA = +25°C)
……………………………………………....2.5W
Junction Temperature...............................150°C
Lead Temperature ....................................260°C
Storage Temperature............... -65°C to +150°C
(2)
3) The device is not guaranteed to function outside of its
operating conditions.
4) Measured on JESD51-7, 4-layer PCB.
Recommended Operating Conditions (3)
Supply Voltage VIN ...........................4.5V to 21V
Operating Junct. Temp (TJ)...... -20°C to +125°C
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
2
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = +25°C, unless otherwise noted.
Parameters
Symbol
IIN
Condition
Min
Typ
Max
Units
μA
Supply Current (Shutdown)
Supply Current (Quiescent)
HS Switch On Resistance
LS Switch On Resistance
VEN = 0V
10
Iq
VEN = 2V, VFB = 1V
0.7
120
20
mA
HSRDS-ON
LSRDS-ON
mΩ
mΩ
VEN = 0V, VSW = 0V or
12V
Switch Leakage
SWLKG
0
10
μA
Current Limit (5)
ILIMIT
FSW
5
6.1
500
0.25
90
7.4
A
kHz
fSW
%
Oscillator Frequency
Fold-back Frequency
Maximum Duty Cycle
Sync Frequency Range
Feedback Voltage
VFB = 0.75V
VFB = 300mV
VFB = 700mV
425
575
FFB
DMAX
FSYNC
VFB
85
0.3
789
2
MHz
mV
nA
V
805
10
1.3
0.4
2
821
50
TA = -20°C to + 85°C
Feedback Current
IFB
VFB = 800mV
EN Rising Threshold
EN Threshold Hysteresis
VEN_RISING
VEN_HYS
1
1.6
V
VEN = 2V
EN Input Current
IEN
μA
VEN = 0V
0
EN Turn Off Delay
ENTd-Off
INUVVth
5
μs
VIN Under Voltage Lockout
Threshold Rising
3.8
4.0
4.2
6.5
V
VIN Under Voltage Lockout
Threshold Hysteresis
INUVHYS
VCC
880
mV
VCC Regulator
5
5
V
%
VCC Load Regulation
Soft-Start Period
Thermal Shutdown
Icc=2mA
2
4
ms
°C
TSD
150
Note:
5) Guaranteed by design.
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
3
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
PIN FUNCTIONS
Pin #
Name
Description
Supply Voltage. The MP8709 operates from a +4.5V to +21V input rail. C1 is
needed to decouple the input rail. Use wide PCB trace to make the connection.
1
IN
2,3
4
SW
Switch Output. Use wide PCB trace to make the connection.
Bootstrap. A capacitor connected between SW and BS pins is required to form a
floating supply across the high-side switch driver.
BST
EN=1 to enable the chip. External clock can be applied to EN pin for changing
switching frequency. For automatic start-up, connect EN pin to VIN by proper EN
resistor divider as Figure 2 shows.
5
6
EN/SYNC
Feedback. An external resistor divider from the output to GND, tapped to the FB
pin, sets the output voltage. To prevent current limit run away during a short
circuit fault condition the frequency fold-back comparator lowers the oscillator
frequency when the FB voltage is below 500mV.
FB
Bias Supply. Decouple with 0.1μF~0.22μF cap. And the capacitance should be
no more than 0.22μF
7
8
VCC
System Ground. This pin is the reference ground of the regulated output voltage.
For this reason care must be taken in PCB layout. Suggested to be connected to
GND with copper and vias.
GND,
Exposed Pad
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
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© 2011 MPS. All Rights Reserved.
4
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, VOUT = 1.2V, L=1.8μH, TA = +25ºC, unless otherwise noted.
Disabled Supply Current vs
Input Voltage
Enabled Supply Current vs
Input Voltage
Vcc Regulator Line Regulation
5.5
5
0.2
0.15
0.1
750
745
740
735
730
725
720
715
710
705
700
0.05
0
4.5
4
-0.05
-0.1
-0.15
-0.2
3.5
0
5
10
15
20
25
0
5
10
15
20
25
0
5
10
15
20
25
Load Regulation
Peak Current vs
Duty Cycle
Operating Range
0.1
0.05
0
7
6.8
6.6
6.4
6.2
6
100
10
V
=4.5V
IN
Dmax Limit
VIN=12V
V
=21V
IN
-0.05
-0.1
-0.15
-0.2
5.8
5.6
5.4
5.2
5
1
Minimum on time Limit
0.1
0 10 20 30 40 50 60 70 80 90100
0
5
10
15
20
25
0
1
2
3
4
Case Temperature Rise vs.
Output Current
Line Regulation
0.2
0.15
0.1
50
40
30
20
10
0
Io=0A
0.05
0
Io=2A
Io=4A
-0.05
-0.1
-0.15
-0.2
0
5
10
15
20
25
0
1
2
3
4
5
.
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
5
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
TYPICAL PERFORMANCE CHARACTERISTICS (continues)
VIN = 12V, VOUT = 1.2V, L=1.8μH, TA = +25ºC, unless otherwise noted.
Efficiency
VOUT=1.8V
Efficiency
VOUT=1.2V
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
V
=4.5V
V
=4.5V
IN
IN
V
=12V
IN
V
=12V
IN
V
=21V
IN
V
=21V
IN
0
0.5
1
1.5
2
2.5
3
3.5
4
0
0.5
1
1.5
2
2.5
3
3.5
4
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Efficiency
VOUT=3.3V
Efficiency
VOUT=2.5V
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
V
=4.5V
IN
V
=21V
V
=4.5V
IN
IN
V
=12V
IN
V
=12V
IN
V
=21V
IN
0
0.5
1
1.5
2
2.5
3
3.5
4
0
0.5
1
1.5
2
2.5
3
3.5
4
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
6
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
TYPICAL PERFORMANCE CHARACTERISTICS (continues)
VIN = 12V, VOUT = 1.2V, L=1.8μH, TA = +25ºC, unless otherwise noted.
Short Entry
Power up without Load
Short Recovery
V
OUT
1V/div
V
OUT
V
OUT
1V/div
1V/div
V
SW
10V/div
V
V
SW
SW
10V/div
V
10V/div
IN
10V/div
INDUCTOR
5A/div
I
I
INDUCTOR
5A/div
I
INDUCTOR
5A/div
2ms/div
10ms/div
4ms/div
Enable Startup
without Load
Enable Startup
with 4A Load
Power up with 4A Load
V
V
OUT
1V/div
V
OUT
1V/div
OUT
1V/div
V
SW
V
V
SW
SW
10V/div
10V/div
10V/div
V
V
EN
V
IN
EN
5V/div
10V/div
5V/div
I
I
INDUCTOR
5A/div
I
INDUCTOR
5A/div
INDUCTOR
5A/div
4ms/div
10ms/div
10ms/div
Load Transient Response
IOUT=2A to 4A
Output Ripple Voltage
IOUT=4A
Input Ripple Voltage
IOUT=4A
V
OUT/AC
V
OUT/AC
50mV/div
VIN/AC
20mV/div
100mV/div
V
SW
5V/div
V
SW
5V/div
I
LOAD
2A/div
I
INDUCTOR
5A/div
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
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© 2011 MPS. All Rights Reserved.
7
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
BLOCK DIAGRAM
IN
+
-
VCC
Regulator
Current Sense
Amplifer
VCC
BOOST
BST
SW
Regulator
Oscillator
HS
Driver
M1
LOGIC
+
-
VCC
Current Limit
Comparator
1pF
Reference
EN/SYNC
FB
LS
Driver
M2
50pF 400K
1MEG
+
+
+
-
+
-
-
PWM Comparator
LS ILIM
Comparator
Error Amplifier
GND
Figure 1—Functional Block Diagram
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
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© 2011 MPS. All Rights Reserved.
8
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
OPERATION
The MP8709 is a high frequency synchronous
rectified step-down switch mode converter with
built in internal 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.
EN/SYNC input low voltage (0.4V). To disable
the chip, EN must be pulled low for at least 5µs.
The input is compatible with both CMOS and TTL.
2) Enabled by Vin through voltage divider.
Connect EN with Vin through a resistive voltage
divider for automatic startup as the figure 2
shows.
The MP8709 operates in a fixed frequency, peak
current control mode to regulate the output
voltage. A PWM cycle is initiated by the internal
clock. The integrated high-side power MOSFET
is turned on and remains on until its current
reaches the value set by the COMP voltage.
When the power switch is off, it remains off until
the next clock cycle starts. If, in 90% of one PWM
period, the current in the power MOSFET does
not reach the COMP set current value, the power
MOSFET will be forced to turn off
V
IN
R
EN1
EN
R
EN2
Figure 2—Enable Divider Circuit
Choose the value of the pull-up resistor REN1 and
pull-down resistor REN2 to reset the automatic
start-up voltage:
Internal Regulator
(REN1 + REN2 ||1MΩ)
V
= VEN_RISING ⋅
IN_START
Most of the internal circuitries are powered from
the 5V internal regulator. This regulator takes the
VIN input and operates in the full VIN range.
When VIN is greater than 5.0V, the output of the
regulator is in full regulation. When VIN is lower
than 5.0V, the output decreases, a 0.1uF ceramic
capacitor for decoupling purpose is required.
REN2 ||1MΩ
Where VEN_RISING is 1.3V
(REN1 + REN2 ||1MΩ)
REN2 ||1MΩ
Where VEN_FALLING is 0.9V
For example, REN1=100kꢀ and REN2=20kꢀ, the
IN-START is set at 7.9V, VIN-STOP is set at 5.49V.
V
=
VEN-FALLING ⋅
IN_STOP
V
Error Amplifier
The startup sequence is as below using the EN
divider. VCC-Rising is the VCC UVLO rising
threshold which is about 4.0V.
The error amplifier compares the FB pin voltage
with the internal 0.805V reference (REF) and
outputs a current proportional to the difference
between the two. This output current is then used
to charge or discharge the internal compensation
network to form the COMP voltage, which is used
to control the power MOSFET current. The
optimized
internal
compensation
network
minimizes the external component counts and
simplifies the control loop design.
Enable/Sync Control
EN/Sync is a digital control pin that turns the
regulator on and off. Drive EN high to turn on the
regulator, drive it low to turn it off. There is an
internal 1MEG resistor from EN/Sync to GND
thus EN/Sync can be floated to shut down the
chip.
Figure 3—Startup Sequence Using EN Divider
3) Synchronized by External Sync Clock Signal
The chip can be synchronized to external clock
range from 300kHz up to 2MHz through this pin
2ms right after output voltage is set, with the
1) Enabled by external logic H/L signal
The chip starts up once the enable signal goes
higher than EN/SYNC input high voltage (2V),
and is shut down when the signal is lower than
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
9
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
internal clock rising edge synchronized to the
external clock rising edge.
Thermal shutdown is implemented to prevent the
chip from operating at exceedingly high
temperatures. When the silicon die temperature
is higher than 150°C, it shuts down the whole
chip. When the temperature is lower than its
lower threshold, typically 140°C, the chip is
enabled again.
Floating Driver and Bootstrap Charging
The floating power MOSFET driver is powered by
an external bootstrap capacitor. This floating
driver has its own UVLO protection. This UVLO’s
rising threshold is 2.2V with a hysteresis of
150mV. The bootstrap capacitor voltage is
regulated internally by VIN through D1, M3, C4,
L1 and C2 (Figure 2). If (VIN-VSW) is more than
5V, U2 will regulate M3 to maintain a 5V BST
voltage across C4.
Figure 4—Startup Sequence Using External
Sync Clock Signal
Under-Voltage Lockout (UVLO)
Under-voltage lockout (UVLO) is implemented to
protect the chip from operating at insufficient
supply voltage. The MP8709 UVLO comparator
monitors the output voltage of the internal
regulator, VCC. The UVLO rising threshold is
about 4.0V while its falling threshold is a
consistent 3.2V.
Internal Soft-Start
The soft-start is implemented to prevent the
converter output voltage from overshooting
during startup. When the chip starts, the internal
circuitry generates a soft-start voltage (SS)
ramping up from 0V to 1.2V. When it is lower
than the internal reference (REF), SS overrides
REF so the error amplifier uses SS as the
reference. When SS is higher than REF, REF
regains control. The SS time is internally fixed to
4ms.
SW
Figure 2—Internal Bootstrap Charging Circuit
Startup and Shutdown
If both VIN and EN are higher than their
appropriate thresholds, the chip starts. The
reference block starts first, generating stable
reference voltage and currents, and then the
internal regulator is enabled. The regulator
provides stable supply for the remaining
circuitries.
Over-Current-Protection and Hiccup
The MP8709 has cycle-by-cycle over current limit
when the inductor current peak value exceeds
the set current limit threshold. Meanwhile, output
voltage starts to drop until FB is below the Under-
Voltage (UV) threshold, typically 30% below the
reference. Once a UV is triggered, the MP8709
enters hiccup mode to periodically restart the part.
This protection mode is especially useful when
the output is dead-short to ground. The average
short circuit current is greatly reduced to alleviate
the thermal issue and to protect the regulator.
The MP8709 exits the hiccup mode once the
over current condition is removed.
Three events can shut down the chip: EN low,
VIN low and thermal shutdown. In the shutdown
procedure, the signaling path is first blocked to
avoid any fault triggering. The COMP voltage and
the internal supply rail are then pulled down. The
floating driver is not subject to this shutdown
command.
Thermal Shutdown
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
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© 2011 MPS. All Rights Reserved.
10
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
APPLICATION INFORMATION
VOUT × (VIN − VOUT
VIN × ΔIL × fOSC
)
Setting the Output Voltage
L =
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 40.2kꢀ for
optimal transient response. R2 is then given by:
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:
ΔIL
IL(MAX) = ILOAD
+
R1
R2 =
2
VOUT
Under light load conditions below 100mA, larger
inductance is recommended for improved
efficiency.
−1
VFB
The T-type network is highly recommended when
Vo is low, as Figure 3 shows.
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.
R1
Rt
1
FB
VOUT
R2
Figure 3— T-type Network
Table 1 lists the recommended T-type resistors
value for common output voltages.
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:
Table 1—Resistor Selection for Common
Output Voltages
VOUT R1
R2
Rt
L
COUT
(V) (kΩ)
(kΩ)
(kΩ)
(μH) (μF, Ceramic)
⎛
⎞
⎟
VOUT
VIN
VOUT
VIN
1.05 4.99
1.2 4.99
1.5 4.99
1.8 4.99
16.5
10.2
5.76
4.02
4.75
3.24
1.91
56
56
47
47
30
20
15
1-4.7
1-4.7
1-4.7
1-4.7
1-4.7
1-4.7
1-4.7
47
47
47
47
47
47
47
⎜
IC1 = ILOAD
×
× 1−
⎜
⎝
⎟
⎠
The worse case condition occurs at VIN = 2VOUT,
where:
ILOAD
2.5
3.3
5
10
10
10
IC1
=
2
For simplification, choose the input capacitor
whose RMS current rating greater than half of the
maximum load current.
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.
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
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 15mꢀ. For
most designs, the inductance value can be
derived from the following equation.
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
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11
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
2) Keep the connection of input capacitor and
capacitors, make sure that they have enough
IN pin as short and wide as possible.
capacitance to provide sufficient charge to
prevent excessive voltage ripple at input. The
input voltage ripple caused by capacitance can
be estimated by:
3) Ensure all feedback connections are short
and direct. Place the feedback resistors
and compensation components as close to
the chip as possible.
⎛
⎜
⎝
⎞
⎟
⎟
⎠
ILOAD
VOUT
VIN
VOUT
⎜
ΔV
=
×
× 1−
IN
fS × C1
V
IN
4) Route SW away from sensitive analog
areas such as FB.
Selecting the Output Capacitor
5) Connect IN, SW, and especially GND
respectively to a large copper area to cool
the chip to improve thermal performance
and long-term reliability.
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:
6) Adding RC snubber circuit from IN pin to
SW pin can reduce SW spikes.
GND
⎛
⎜
⎝
⎞
⎟
⎟
⎛
⎜
⎝
⎞
⎟
⎟
⎠
VOUT
VOUT
VIN
1
⎜
⎜
ΔVOUT
=
× 1−
× RESR
+
C2
fS × L
8 × fS × C2
⎠
Where L is the inductor value and RESR is the
equivalent series resistance (ESR) value of the
output capacitor.
R
2
ON/OFF
EN
BST
SW
SW
IN
L1
FB
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:
VCC
GND
C1
⎛
⎜
⎝
⎞
⎟
⎟
⎠
VOUT
8 × fS2 × L × C2
VOUT
⎜
ΔVOUT
=
× 1−
Top Layer
V
IN
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:
VOUT
VOUT
VIN
⎛
⎞
ΔVOUT
=
× ⎜1−
⎟ ×RESR
⎜
⎟
fS ×L
⎝
⎠
The characteristics of the output capacitor also
affect the stability of the regulation system. The
MP8709 can be optimized for a wide range of
capacitance and ESR values.
Bottom Layer
PCB Layout
PCB layout is very important to achieve stable
operation. Please follow these guidelines and
take Figure 4 for references.
Figure 4—PCB Layout
1) Keep the connection of input ground and
GND pin as short and wide as possible.
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
12
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
External Bootstrap Diode
An external bootstrap diode may enhance the
efficiency of the regulator, the applicable
conditions of external BST diode is:
VOUT
z Duty cycle is high: D=
>65%
VIN
In this case, an external BST diode is
recommended from the VCC pin to BST pin, as
shown in Figure 5
External BST Diode
IN4148
BST
VCC
CBST
MP8709
SW
L
COUT
Figure 5—Add Optional External Bootstrap
Diode to Enhance Efficiency
The recommended external BST diode is
IN4148, and the BST cap is 0.1~1µF.
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
13
MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
PACKAGE INFORMATION
SOIC8E (EXPOSED PAD)
0.189(4.80)
0.197(5.00)
0.124(3.15)
0.136(3.45)
8
5
0.150(3.80)
0.157(4.00)
0.228(5.80)
0.244(6.20)
0.089(2.26)
0.101(2.56)
PIN 1 ID
1
4
TOP VIEW
BOTTOM VIEW
SEE DETAIL "A"
0.051(1.30)
0.067(1.70)
SEATING PLANE
0.000(0.00)
0.006(0.15)
0.0075(0.19)
0.0098(0.25)
0.013(0.33)
0.020(0.51)
SIDE VIEW
0.050(1.27)
BSC
FRONT VIEW
0.010(0.25)
0.020(0.50)
x 45o
GAUGE PLANE
0.010(0.25) BSC
0.050(1.27)
0.024(0.61)
0.063(1.60)
0.016(0.41)
0.050(1.27)
0o-8o
DETAIL "A"
0.103(2.62)
0.213(5.40)
NOTE:
1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN
BRACKET IS IN MILLIMETERS.
2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH,
PROTRUSIONS OR GATE BURRS.
3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH
OR PROTRUSIONS.
0.138(3.51)
4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING)
SHALL BE 0.004" INCHES MAX.
5) DRAWING CONFORMS TO JEDEC MS-012, VARIATION BA.
6) DRAWING IS NOT TO SCALE.
RECOMMENDED LAND PATTERN
NOTICE: The information in this document is subject to change without notice. Users should warrant and guarantee that third
party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not
assume any legal responsibility for any said applications.
MP8709 Rev. 1.01
12/14/2011
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
14
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