MP8718
High Efficiency 4A, 21V, 500kHz
Synchronous Step-down Converter
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP8718 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. The
MP8718 has synchronous mode operation for
higher efficiency over output current load range.
•
•
•
•
•
•
•
•
•
•
•
•
•
Current mode operation provides fast transient
response and eases loop stabilization.
Full protection features include OCP and
thermal shut down.
The MP8718 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.
Wide 4.5V to 21V Operating Input Range
4A Output Current
Low Rds(on) Internal Power MOSFETs
Proprietary Switching Loss Reduction
Technique
High Efficiency Synchronous Mode Operation
Fixed 500kHz Switching Frequency
Sync from 300kHz to 2MHz External Clock
1.5ms Internal Soft-Start
Internal Compensation
OCP Protection and Hiccup
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
“MPS” and “The Future of Analog IC Technology” are Registered Trademarks of
Monolithic Power Systems, Inc.
The information in this datasheet about the product and its associated
technologies are proprietary and intellectual property of Monolithic Power
Systems and are protected by copyright and pending patent applications
TYPICAL APPLICATION
Efficiency
VOUT=1.2V
21
VIN
100
1
IN
BST
4
V IN=5V
90
SW
7
VCC
ON/OFF
VOUT 1.2V
MP8718
R1
4.99k
FB
5
2,3
EN/SYNC
6
Rt
47k
R2
10k
EFFICIENCY (%)
80
70
V IN=21V
60
V IN=12V
50
40
30
20
GND
10
8
0
0
1
2
3
4
OUTPUT CURRENT (A)
MP8718 Rev. 0.9
4/12/2016
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
1
MP8718 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
ORDERING INFORMATION
Part Number*
Package
Top Marking
Free Air Temperature (TA)
MP8718EN
SOIC8E
MP8718EN
-20°C to +85°C
* For Tape & Reel, add suffix –Z (e.g. MP8718EN–Z);
For RoHS compliant packaging, add suffix –LF; (e.g. MP8718EN–LF–Z)
PACKAGE REFERENCE
TOP VIEW
IN
1
8
GND
SW
2
7
VCC
SW
3
6
FB
BST
4
5
EN/SYNC
EXPOSED PAD
ON BACKSIDE
CONNECT TO GND
ABSOLUTE MAXIMUM RATINGS (1)
Supply Voltage VIN ....................................... 22V
VSW ........................-0.3V (-5V for < 10ns) to 23V
VBS ....................................................... VSW + 6V
All Other Pins ..................................-0.3V to +6V
Operating Temperature.............. -20°C to +85°C
(2)
Continuous Power Dissipation (TA = +25°C)
……………………………………………....2.5W
Junction Temperature ...............................150°C
Lead Temperature ....................................260°C
Storage Temperature............... -65°C to +150°C
Recommended Operating Conditions
(3)
Thermal Resistance
(4)
θJA
θJC
SOIC8E (Exposed Pad) ..........50 ...... 10 ... °C/W
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-toambient 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.
3) The device is not guaranteed to function outside of its
operating conditions.
4) Measured on JESD51-7, 4-layer PCB.
Supply Voltage VIN ...........................4.5V to 21V
Operating Junct. Temp (TJ)...... -20°C to +125°C
MP8718 Rev. 0.9
4/12/2016
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
2
MP8718 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = +25°C, unless otherwise noted.
Parameters
Supply Current (Shutdown)
Supply Current (Quiescent)
HS Switch On Resistance (5)
LS Switch On Resistance (5)
Switch Leakage
Current Limit (5)
Oscillator Frequency
Fold-back Frequency
Maximum Duty Cycle
Sync Frequency Range
Symbol
IIN
IQ
HSRDS-ON
LSRDS-ON
SWLKG
ILIMIT
FSW
FFB
DMAX
FSYNC
Feedback Voltage
VFB
Feedback Current
EN Rising Threshold
EN Threshold Hysteresis
IFB
EN Input Current
Min
VEN = 0V, VSW = 0V or 12V
VFB = 0.75V
VFB = 300mV
VFB = 700mV
425
TA = -20°C to +85°C
VFB = 800mV
789
VEN_RISING
VEN_HYS
IEN
EN Turn Off Delay
VIN Under Voltage Lockout
Threshold Rising
VIN Under Voltage Lockout
Threshold Hysteresis
VCC Regulator
VCC Load Regulation
Soft-Start Period
Thermal Shutdown
Condition
VEN = 0V
VEN = 2V, VFB = 1V
85
0.3
1.1
VEN = 2V
VEN = 0V
ENTd-Off
3.8
INUVVth
INUVHYS
VCC
Icc=2mA
TSD
Typ
2
Units
μA
mA
mΩ
mΩ
μA
A
kHz
fSW
%
MHz
805
821
mV
10
1.3
0.4
2
0
5
50
1.6
nA
V
V
4.0
4.2
0.7
120
20
0
6.1
500
0.25
90
Max
10
10
575
μA
μs
V
880
mV
5
5
1.5
150
V
%
ms
°C
2
Note:
5) Guaranteed by design.
MP8718 Rev. 0.9
4/12/2016
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
3
MP8718 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
PIN FUNCTIONS
Pin #
1
2,3
4
5
6
7
8
MP8718 Rev. 0.9
4/12/2016
Name
Description
Supply Voltage. The MP8718 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.
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
BST
floating supply across the high-side switch driver.
EN=1 to enable the chip. External clock can be applied to EN pin for changing
EN/SYNC
switching frequency. For automatic start-up, connect EN pin to VIN by proper EN
resistor divider as Figure 2 shows.
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
FB
circuit fault condition the frequency fold-back comparator lowers the oscillator
frequency when the FB voltage is below 500mV.
Bias Supply. Decouple with 0.1uF~0.22μF cap. And the capacitance should be
VCC
no more than 0.22μF
System Ground. This pin is the reference ground of the regulated output voltage.
GND,
For this reason care must be taken in PCB layout. Suggested to be connected to
Exposed Pad
GND with copper and vias.
IN
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
4
MP8718 – 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
750
0.2
745
0.15
740
735
5.5
5
0.1
725
0
720
-0.05
715
710
VCC (V)
0.05
730
VEN=0V
-0.15
VFB=1V
3.5
-0.2
700
5
10
15
20
25
0
5
10
15
20
Peak Current vs
Duty Cycle
100
6.6
6.4
6.2
6
5.8
5.6
5.4
5.2
5
Dmax Limit
10
1
Minimum on time Limit
0.1
0 10 20 30 40 50 60 70 80 90100
0
5
DUTY CYCLE (%)
10
15
10
15
20
25
Load Regulation
Operating Range
OUTPUT VOLTAGE (V)
PEAK CURRENT (A)
5
INPUT VOLTAGE (V)
6.8
20
25
INPUT VOLTAGE (V)
0.4
0.3
VIN=4.5V
0.2
0.1
0.0
-0.1
VIN=21V
VIN=12V
-0.2
-0.3
-0.4
0 0.5
1 1.5
2 2.5
3 3.5
4
OUTPUT CURRENT (A)
Case Temperature Rise vs.
Output Current
Line Regulation
NORMALIZED OUTPUT VOLTAGE(%)
0
25
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
NORMALIZED OUTPUT VOLTAGE(%)
0
4.5
4
-0.1
705
7
Vcc Regulator Line Regulation
0.3
25
0.2
20
IO=0A
0.1
15
0.0
IO=2A
10
-0.1
IO=4A
-0.2
5
-0.3
0
0
5
10
15
20
INPUT CURRENT (V)
MP8718 Rev. 0.9
4/12/2016
25
0
1
2
3
4
5
OUTPUT CURRENT (A)
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
5
MP8718 – 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
Efficiency
VOUT=1.2V
100
VOUT=1.8V
100
V IN=5V
90
80
80
70
V IN=21V
60
EFFICIENCY (%)
EFFICIENCY (%)
V IN=5V
90
V IN=12V
50
40
30
20
10
V IN=21V
70
60
V IN=12V
50
40
30
20
10
0
0
1
2
3
0
4
0
Efficiency
100
90
90
80
V IN=5V
EFFICIENCY (%)
EFFICIENCY (%)
60
V IN=12V
50
40
30
20
V IN=21V
70
V IN=5V
V IN=12V
60
50
40
30
20
10
10
0
0
0
MP8718 Rev. 0.9
4/12/2016
4
VOUT=3.3V
100
V IN=21V
3
Efficiency
VOUT=2.5V
70
2
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
80
1
1
2
3
OUTPUT CURRENT (A)
4
0
1
2
3
4
OUTPUT CURRENT (A)
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
6
MP8718 – 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
VOUT
1V/div
VOUT
1V/div
VOUT
1V/div
VSW
10V/div
VSW
10V/div
VSW
10V/div
VIN
10V/div
IINDUCTOR
5A/div
IINDUCTOR
5A/div
IINDUCTOR
5A/div
Power up with 4A Load
1ms/div
1ms/div
Enable Startup
without Load
Enable Startup
with 4A Load
VOUT
1V/div
VOUT
1V/div
VOUT
1V/div
VSW
10V/div
VSW
10V/div
VSW
10V/div
VIN
10V/div
VEN
5V/div
VEN
5V/div
IINDUCTOR
5A/div
IINDUCTOR
5A/div
IINDUCTOR
5A/div
1ms/div
1ms/div
Input Ripple Voltage
Output Ripple Voltage
IOUT=4A
IOUT=4A
VIN/AC
100mV/div
VOUT/AC
10mV/div
VSW
10V/div
VSW
5V/div
MP8718 Rev. 0.9
4/12/2016
IINDUCTOR
2A/div
1ms/div
Load Transient Response
IOUT=2A to 4A
VOUT/AC
50mV/div
VSW
10V/div
ILOAD
2A/div
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
7
MP8718 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
BLOCK DIAGRAM
IN
+
VCC
Regulator
VCC
Current Sense
Amplifer
BOOST
Regulator
Oscillator
BST
HS
Driver
LOGIC
M1
+
SW
-
Reference
1MEG
FB
LS
Driver
400K
+
+
Error Amplifier
M2
+
PWM Comparator
LS ILIM
Comparator
-
50pF
+
EN/SYNC
VCC
Current Limit
Comparator
1pF
GND
Figure 1—Functional Block Diagram
MP8718 Rev. 0.9
4/12/2016
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
8
MP8718 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
OPERATION
The MP8718 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.
The MP8718 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
Internal Regulator
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.
Error Amplifier
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.
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
MP8718 Rev. 0.9
4/12/2016
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.
VIN
REN1
EN
REN2
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:
VIN_START = VEN_RISING ⋅
Where VEN_RISING is 1.3V
VIN_STOP = VEN-FALLING ⋅
(REN1 + REN2 || 1MΩ)
REN2 || 1MΩ
(REN1 + REN2 || 1MΩ)
REN2 || 1MΩ
Where VEN_FALLING is 0.9V
For example, REN1=100kΩ and REN2=20kΩ, the
VIN-START is set at 7.9V, VIN-STOP is set at 5.49V.
The startup sequence is as below using the EN
divider. VCC-Rising is the VCC UVLO rising
threshold which is about 4.0V.
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
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
9
MP8718 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
internal clock rising edge synchronized to the
external clock rising edge.
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 MP8718 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.
Over-Current-Protection and Hiccup
The MP8718 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 UnderVoltage (UV) threshold, typically 30% below the
reference. Once a UV is triggered, the MP8718
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 MP8718 exits the hiccup mode once the
over current condition is removed.
MP8718 Rev. 0.9
4/12/2016
Thermal Shutdown
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.
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.
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.
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
10
MP8718 – 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 =
1
VOUT
−1
VFB
R1
Rt
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
(V)
1.05
1.2
1.5
1.8
2.5
3.3
5
R1
(kΩ)
4.99
4.99
4.99
4.99
82
82.5
54.9
R2
(kΩ)
16.5
10.2
5.76
4.02
39.2
26.7
10.5
Rt
(kΩ)
47
47
47
47
0
0
0
L
(μH)
1-4.7
1-4.7
1-4.7
1-4.7
1-4.7
1-4.7
1-4.7
COUT
(μF, Ceramic)
47
47
47
47
47
47
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.
MP8718 Rev. 0.9
4/12/2016
VOUT × ( VIN − VOUT )
VIN × ΔIL × f OSC
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 +
R1
The T-type network is highly recommended when
Vo is low, as Figure 3 shows.
FB
L=
ΔI L
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:
I C1 = ILOAD ×
VOUT ⎛⎜ VOUT
× 1−
VIN
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
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:
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
11
MP8718 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
⎛
I
V
V
ΔVIN = LOAD × OUT × ⎜⎜1 − OUT
fS × C1 VIN ⎝
VIN
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:
ΔVOUT
⎛
V
V
= OUT × ⎜⎜1 − OUT
fS × L ⎝
VIN
3)
Ensure all feedback connections are short
and direct. Place the feedback resistors
and compensation components as close to
the chip as possible.
4)
Route SW away from sensitive analog
areas such as FB.
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.
6)
Adding RC snubber circuit from IN pin to
SW pin can reduce SW spikes.
⎞
⎟⎟
⎠
⎞
⎞ ⎛
1
⎟
⎟⎟ × ⎜ R ESR +
⎜
8 × f S × C2 ⎟⎠
⎠ ⎝
ΔVOUT =
8 × fS
2
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 ⎛
V
× ⎜1 − OUT
f S × L ⎜⎝
VIN
4
C4
5
3
6
Rt
2
7
1
8
⎞
⎛
V
× ⎜⎜1 − OUT ⎟⎟
VIN ⎠
× L × C2 ⎝
VOUT
C
3
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:
R
1
Where L is the inductor value and RESR is the
equivalent series resistance (ESR) value of the
output capacitor.
Top Layer
⎞
⎟⎟ × R ESR
⎠
The characteristics of the output capacitor also
affect the stability of the regulation system. The
MP8718 can be optimized for a wide range of
capacitance and ESR values.
PCB Layout
PCB layout is very important to achieve stable
operation. Please follow these guidelines and
take Figure 4 for references.
1)
Keep the connection of input ground and
GND pin as short and wide as possible.
2)
Keep the connection of input capacitor and
IN pin as short and wide as possible.
Bottom Layer
Figure 4—PCB Layout
MP8718 Rev. 0.9
4/12/2016
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
12
MP8718 – 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:
z
Duty cycle is high: D=
VOUT
>65%
VIN
In this case, an external BST diode is
recommended from the VCC pin to BST pin, as
shown in Figure 5
BST
MP8718
SW
External BST Diode
IN4148
VCC
CBST
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.
MP8718 Rev. 0.9
4/12/2016
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
13
MP8718 – 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)
PIN 1 ID
1
0.228(5.80)
0.244(6.20)
0.089(2.26)
0.101(2.56)
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)
0.013(0.33)
0.020(0.51)
0.0075(0.19)
0.0098(0.25)
SIDE VIEW
0.050(1.27)
BSC
FRONT VIEW
0.010(0.25)
x 45o
0.020(0.50)
GAUGE PLANE
0.010(0.25) BSC
0.050(1.27)
0.024(0.61)
0o-8o
0.016(0.41)
0.050(1.27)
0.063(1.60)
DETAIL "A"
0.103(2.62)
0.138(3.51)
RECOMMENDED LAND PATTERN
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.
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.
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.
MP8718 Rev. 0.9
4/12/2016
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
14
工商网监
湘ICP备2023018690号
