MP28266 [MPS]
21V, 3A, 500kHz, Synchronous Step-Down Converter;
| 型号： | MP28266 |
| 厂家： | 
MONOLITHIC POWER SYSTEMS |
| 描述： | 21V, 3A, 500kHz, Synchronous Step-Down Converter |
| 文件： | 总14页 (文件大小：284K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MP28266
21V, 3A, 500kHz, Synchronous
Step-Down Converter
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP28266 is a synchronous, rectified, step-
down, switch-mode converter with built in
internal power MOSFETs. It offers a very
compact solution to achieve a 3A continuous
output current over a wide input supply range,
with excellent load and line regulation. The
MP28266 has synchronous mode operation for
higher efficiency over the output-current–load
range.
Wide 6V-to-21V Operating Input Range
0.6V Internal Reference with 2% Accuracy
3A Output Current
Low-Rds(ON) Internal Power MOSFETs
Fixed 500kHz Switching Frequency
Frequency SYNC from a 300kHz-to-2MHz
External Clock
External Soft-Start
AAM Power-Save Mode
OCP and Thermal Shutdown
Available in a 3mm×4mm QFN14 Package.
Current-mode operation provides
a
fast
transient response and eases loop stabilization.
Full protection features include over-current
protection and thermal shutdown.
APPLICATIONS
DSL Modems
Cable Modems
Set Top Boxes
The MP28266 requires a minimal number of
readily-available standard external components,
and is available in a space-saving 3mm×4mm
14-pin QFN package.
All MPS parts are lead-free and adhere to the RoHS directive. For MPS green
status, please visit MPS website under Quality Assurance. “MPS” and “The
Future of Analog IC Technology” are Registered Trademarks of Monolithic
Power Systems, Inc.
TYPICAL APPLICATION
6V-21V
1
6
VIN
IN
BST
SW
C1B
0.1
C3
0.1 F
C1A
22 F
L1
2.8 H
1.2V/3A
2,3,4,5
11
VCC
VOUT
C2A
22 F
C4
0.1 F
R4
90.9k
R1
10k
MP28266
7
9
8
AAM
AAM
FB
SS
C5
1 F
R8
24k
R3
10k
10
R2
10k
SYNC
C7
47nF
SYNC
MP28266 Rev. 1.0
3/16/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
1
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
ORDERING INFORMATION
Part Number*
Package
Top Marking
Free Air Temperature (TA)
MP28266DL
QFN14 (3x4mm)
MP28266DL
-40°C to +85°C
* For Tape & Reel, add suffix –Z (eg. MP28266DL–Z);
For RoHS, compliant packaging, add suffix –LF (eg. MP28266DL–LF–Z).
PACKAGE REFERENCE
TOP VIEW
PIN 1 ID
IN
SW
1
2
3
4
5
6
7
14 AGND
13 GND
12 GND
11 VCC
SW
Exposed
Pad
SW
SW
SS
10
9
BST
SYNC
AAM
FB
8
QFN14 (3x4mm)
ABSOLUTE MAXIMUM RATINGS (1)
VIN ..................................................-0.3V to 24V
Thermal Resistance (4)
QFN14 (3x4mm) .....................48 ...... 11...°C/W
θJA
θJC
V
V
SW..................................................-0.3V to 24V
BST ...................................................... 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
Junction Temperature...............................150°C
Lead Temperature ....................................260°C
Junction Temperature...............................150°C
Continuous Power Dissipation (TA = +25°C) (2)
............................................................. 2.6W
Recommended Operating Conditions (3)
Supply Voltage VIN ..............................6V to 21V
Output Voltage VOUT.........................0.6V to 18V
Maximum Junction Temp. (TJ)............... +125°C
3) The device is not guaranteed to function outside of its
operating conditions.
4) Measured on JESD51-7, 4-layer PCB.
MP28266 Rev. 1.0
3/16/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
2
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = 25°C, unless otherwise noted.
Parameters
Symbol
Condition
Min
Typ
Max
Units
VIN = 12V, VFB = 1V,
0.55
0.7
0.85
VAAM=5V
Supply Current (Quiescent)
Iq
mA
VIN = 12V, VFB = 1V,
0.45
0.6
0.75
VAAM=0.5V
HS Switch On Resistance
LS Switch On Resistance
HSRDS-ON
LSRDS-ON
120
20
mΩ
mΩ
V
SW = 0V or 12V,
Switch Leakage
SWLKG
0.1
1
μA
VFB =0.7V, VAAM=0.5V
Current Limit(5)
ILIMIT
fSW
D=40%
4.2
5.5
500
80
A
kHz
ns
Oscillator Frequency
Minimum On Time(5)
Maximum Duty Cycle
Sync Frequency Range
VFB=550mV
425
595
tON-MIN
DMAX
fSYNC
VFB = 550mV
85
90
%
0.3
591
588
2
MHz
TA = 25oC
-40oC<TA<85oC(6)
603
603
10
615
618
50
Feedback Voltage
VFB
mV
Feedback Current
AAM-High Threshold
AAM-Low Threshold
IFB
VFB = 650mV
nA
V
VAAM HIGH
VAAM LOW
2.9
2.2
V
VAAM=0V
VAAM=5V
0
μA
μA
V
AAM Input Current
IAAM
3.3
SYNC Input HIGH Level
SYNC Input LOW Level
SYNC Input Current
Soft-Start current
VHI
VLO
ISYNC
ISS
1.8
0.4
V
VSYNC=6V
VSS=0
6
μA
μA
10
VIN Under-Voltage Lockout
Threshold—Rising
INUVVth_rising
5.2
4.1
5.5
4.4
5.8
4.7
V
V
VIN Under-Voltage Lockout
Threshold—Falling
INUVVth_falling
VCC
VCC Regulator
5
5
V
%
°C
VCC Load Regulation
Thermal Shutdown(5)
Icc=5mA
TSD
150
Notes:
5) Guaranteed by design.
6) Not tested in production and guaranteed by over-temperature correlation.
MP28266 Rev. 1.0
3/16/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
3
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS
Performance curves are tested on the evaluation board of the Design Example section.
VIN = 12V, VOUT = 1.2V, VAAM=0.5V, L = 2.8µH, TA = +25°C, unless otherwise noted.
Efficiency vs.
Supply Current vs.
Input Voltage
V =1V
FB
Output Current
I
=0.1A-3A
OUT
100
95
90
85
80
75
70
65
60
55
50
100
95
90
85
80
75
70
65
60
55
50
800.00
700.00
600.00
500.00
400.00
300.00
200.00
V
=6V
IN
V
=12V
IN
V
=6V
IN
V
=12V
IN
V
=21V
IN
V
=21V
IN
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0
5
10
15
20
25
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
INPUT VOLTAGE (V)
Case Temperature Rise vs.
Load Regulation
Line Regulatioin
V
=6V-21V
IN
I
OUT
=0A-3A
I
OUT
1.00
12
0.30
0.80
0.60
0.20
0.10
10
8
I
=0A
OUT
0.40
V
=6V
IN
I
=1.5A
V
=12V
0.20
OUT
IN
0.00
6
4
2
0
0.00
-0.20
-0.40
-0.60
-0.80
-1.00
I
OUT
=3A
V
=21V
IN
-0.10
-0.20
-0.30
0
0.5
1
1.5
2
2.5
3
0
0.5
1
1.5
2
2.5
3
5
7
9
11 13 15 17 19 21 23
INPUT VOLTAGE (V)
LOAD CURRENT (A)
OUTPUT CURRENT (A)
Current Limit vs.
Duty Cycle
7
6.5
6
5.5
5
4.5
4
3.5
3
0 10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
MP28266 Rev. 1.0
3/16/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
4
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Performance curves are tested on the evaluation board of the Design Example section.
VIN = 12V, VOUT = 1.2V, VAAM=0.5V, L = 2.8µH, TA = +25°C, unless otherwise noted.
Short Entry
Short Recovery
Startup through
Input Voltage
I
= 0A
I
= 0A
OUT
OUT
I
= 0A
OUT
V
V
V
OUT
OUT
OUT
500mV/div.
500mV/div.
500mV/div.
V
IN
10V/div.
V
V
SW
SW
10V/div.
10V/div.
V
SW
5V/div.
I
I
L
L
5A/div.
5A/div.
I
INDUCTOR
500mA/div.
Startup through
Input Voltage
Shutdown through
Input Voltage
Shutdown through
Input Voltage
I
= 3A
I
= 0A
I
= 3A
OUT
OUT
OUT
V
V
V
OUT
OUT
OUT
500mV/div.
500mV/div.
500mV/div.
V
V
V
IN
IN
IN
10V/div.
10V/div.
10V/div.
V
V
V
SW
SW
SW
5V/div.
5V/div.
5V/div.
I
I
I
INDUCTOR
INDUCTOR
INDUCTOR
2A/div.
2A/div.
2A/div.
Input/Output Ripple
Load Transient Reponse
I
= 3A
I
= 1.5A-3A
OUT
OUT
V
/AC
OUT
10mV/div.
V
/AC
OUT
50mV/div.
V
/AC
IN
100mV/div.
V
SW
10V/div.
I
L
1A/div.
I
L
2A/div.
MP28266 Rev. 1.0
3/16/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
5
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
PIN FUNCTIONS
QFN14
Name
Pin #
Description
Supply Voltage. The MP28266 operates from a 6V-to-21V input rail. C1 decouples
the input rail. Connect using wide PCB traces and multiple vias.
1
IN
SW
2,3,4,5
Switch Output. Connect using wide PCB traces and multiple vias.
Bootstrap. A capacitor connected between SW and BST pins is required to form a
floating supply across the high-side switch driver.
6
7
BST
SYNC
This pin serves as frequency synchronous clock input.
Feedback. Connect to the tap of an external resistor divider from the output to GND
to set the output voltage. To prevent current-limit runaway during a short circuit fault
condition, the frequency fold-back comparator lowers the oscillator frequency when
the FB voltage is below 100mV.
8
9
FB
Advanced Asynchronous Modulation. Connect to a voltage supply through 2 resistor
dividers to force the MP28266 into non-synchronous mode under light loads. Drive
AAM pin high (VCC) to force the MP28266 into CCM.
AAM
Soft Start. Connect an external capacitor to program the soft start time for the switch
mode regulator.
10
11
SS
VCC
Bias Supply. Decouple with 0.1μF-to-0.22μF capacitor. And the capacitance should
be no more than 0.22μF.
System Ground. This reference ground of the regulated output voltage. Requires
special considerations during PCB layout.
12,13
14
GND
Signal Ground. AGND is not internally connected to System Ground; connect AGND
to system Ground in PCB layout.
AGND
No Internal Connection. Connect the exposed pad to GND plane for optimal thermal
performance.
Exposed Pad
MP28266 Rev. 1.0
3/16/2012
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6
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
BLOCK DIAGRAM
IN
+
-
RSEN
VCC
VCC
Current Sense
Amplifer
Regulator
Bootstrap
Regulator
BST
Oscillator
HS
Driver
+
SW
-
Comparetor
On Time Control
Logic Control
Current Limit
Comparator
VCC
1pF
Reference
400k
50pF
LS
Driver
+
+
-
FB
Error Amplifier
GND
SYNC
SS
AAM
Figure 1: Functional Block Diagram
MP28266 Rev. 1.0
3/16/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
7
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
OPERATION
The MP28266’s UVLO comparator monitors the
output voltage of the internal regulator, VCC. The
UVLO rising threshold is about 5.5V while its
falling threshold is a consistent 4.4V.
The MP28266 is a high-frequency, synchronous,
rectified, step-down, switch-mode converter with
built-in power MOSFETs. It offers a very compact
solution to achieve more than 3A continuous
output current over a wide input supply range,
with excellent load and line regulation.
External Soft-Start
Adjust the soft start time through the capacitor
connected from SS to ground. When the soft-
start period starts, an internal 10µA current
source charges the external capacitor. During
soft-start, the voltage on the soft-start capacitor
connects to the non-inverting input of the error
amplifier. The soft-start period lasts until the
voltage on the soft-start capacitor exceeds the
reference voltage of 0.6V. At this point the
reference voltage takes over at the non-inverting
error amplifier input. The soft-start time can be
calculated as follows:
The MP28266 operates in a fixed-frequency,
peak-current–control mode to regulate the output
voltage. An internal clock initiates the PWM cycle
to turn on the integrated high-side power
MOSFET. This MOSFET 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
within 90% of one PWM period the power
MOSFET current does not reach the COMP-set
current value, the power MOSFET will be forced
to turn off.
0.6V CSS (nF)
tSS (ms)
Error Amplifier
10A
The error amplifier compares the FB pin voltage
against the internal 0.6V reference (REF) and
outputs a current proportional to their difference.
This output current charges or discharges the
internal compensation network for the COMP
voltage, which controls the power MOSFET
current. The optimized internal compensation
network minimizes the external component
counts and simplifies the control loop design.
If the output of the MP28266 is pre-biased to a
certain voltage during startup, the IC will disable
both the high-side and low-side switches until the
voltage on the internal soft-start capacitor
exceeds the sensed output voltage at the FB pin.
Over-Current Protection
The MP28266 has a hiccup over-current limit for
when the inductor current peak value exceeds
the set current limit threshold. When the output
voltage drops below 70% of the reference while
the inductor current exceeds the current limit, the
MP28266 enters hiccup mode. This is especially
useful to ensure system safety under fault
conditions. The latch-off function is disabled
during the soft-start duration.
Internal Regulator
The 5V internal regulator powers most of the
internal circuits. This regulator takes the VIN input
and operates in the full VIN range. When VIN
exceeds 5.0V, the output of the regulator is in full
regulation. When VIN is lower than 5.0V, the
output decreases and requires a 0.1μF ceramic
decoupling capacitor.
Thermal Shutdown
Thermal shutdown prevents the chip from
operating at exceedingly high temperatures.
When the silicon die temperature exceeds
150°C, it shuts down the whole chip. When the
temperature is below its lower threshold—
typically 140°C—the chip is enabled again.
Frequency Synchronizing
The MP28266 can be synchronized through the
SYNC pin to an external clock with a range from
300kHz up to 2MHz. The internal clock rising
edge is synchronized to the external clock rising
edge.
Floating Driver and Bootstrap Charging
Under-Voltage Lockout (UVLO)
Under-voltage lockout (UVLO) protects the chip
against operating at an insufficient supply
voltage.
An external bootstrap capacitor powers the
floating power MOSFET driver. This floating
driver has its own UVLO protection with a rising
MP28266 Rev. 1.0
3/16/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
8
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
threshold of 2.2V and a hysteresis of 150mV. VIN
internally regulates the bootstrap capacitor
voltage through D1, M1, C4, L1 and C2 (Figure
2). If (VIN-VSW) exceeds 5V, U1 regulates M1 to
maintain a 5V BST voltage across C4.
D1
V
IN
M1
BST
U1
5V
C4
V
OUT
SW
L1
C2
Figure 2: Internal Bootstrap Charging Circuit
MP28266 Rev. 1.0
3/16/2012
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© 2012 MPS. All Rights Reserved.
9
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
Where ΔIL is the inductor ripple current.
APPLICATION INFORMATION
Choose inductor current to be approximately
30% of the maximum load current. The maximum
inductor peak current is:
COMPONENT SELECTION
Setting the Output Voltage
The external resistor divider sets the output
voltage (see the Typical Application on page 1).
The feedback resistor R1—with the internal
compensation capacitor—also sets the feedback
loop bandwidth (see the Typical Application on
page 1). Choose R1 equal to 10kΩ. R2 is then:
IL
IL(MAX) ILOAD
2
Under light-load conditions (below 100mA), use a
larger inductance for improved efficiency.
Selecting the Input Capacitor
R1
The input current to the step-down converter is
discontinuous, therefore requires a capacitor to
supply the AC current to the step-down converter
and maintain the DC input voltage. Use low ESR
capacitors; in particular ceramic capacitors with
X5R or X7R dielectrics not only because of their
low ESR values, but also their small temperature
coefficients. A 22µF capacitor will suffice for most
applications.
R2
V
OUT
1
0.6V
The T-type network is highly recommended when
V
OUT is low.
R1
RT
8
FB
VOUT
R2
The input capacitor (C1) requires an adequate
ripple current rating because it absorbs the input
switching current. Estimate the RMS current in
the input capacitor with:
Figure 3: T-Type Network
Table 1 lists the recommended T-type resistors
value for common output voltages.
VOUT
VIN
VOUT
VIN
IC1 ILOAD
1
Table 1: Resistor Selection for Common
Output Voltages
The worst-case condition occurs at VIN = 2VOUT
where:
,
VOUT (V)
1.05
1.2
R1 (kΩ)
7.5(1%)
10(1%)
10(1%)
10(1%)
10(1%)
10(1%)
R2 (kΩ)
Rt (kΩ)
24.9(1%)
24.9(1%)
24.9(1%)
24.9(1%)
24.9(1%)
24.9(1%)
10(1%)
ILOAD
IC1
10(1%)
2
1.8
4.99(1%)
3.16(1%)
2.20(1%)
1.36(1%)
For simplification, choose an input capacitor with
an RMS current rating greater than half the
maximum load current.
2.5
3.3
5
The input capacitor can be electrolytic, tantalum
or ceramic. When using electrolytic or tantalum
capacitors, place a small, high-quality ceramic
capacitor with a value of 0.1μF as close to the IC
as possible. When using ceramic capacitors,
select those with enough capacitance to prevent
excessive input voltage ripple. Estimate the input
voltage ripple caused by the capacitance with:
Selecting the Inductor
For most applications, use a 1µH-to-10µH
inductor with a DC current rating of at least 25%
percent higher than the maximum load current.
For highest efficiency, select an inductor with a
DC resistance less than 15mꢀ. For most
designs, derive the inductance value from the
following equation:
ILOAD
VOUT
VOUT
V
1
IN
fS C1
V
IN
V
IN
VOUT (V VOUT
)
IN
L1
V IL fOSC
IN
MP28266 Rev. 1.0
3/16/2012
www.MonolithicPower.com
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10
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
VCC(5V)
Selecting the Output Capacitor
The output capacitor (C2) maintains the DC
output voltage. Use ceramic, tantalum, or low-
ESR electrolytic capacitors. Use low ESR
capacitors in particular to keep the output voltage
ripple low, as estimated by:
R4
R3
AAM
VOUT
VOUT
1
VOUT
1
R
ESR
Figure 4: AAM Network
fS L1
V
8 fS C2
IN
Normally, the convertor has three operating
modes: AAM, DCM, CCM. The boundary
between DCM and CCM occurs when the
inductor ripple minimum is zero. The input
voltage, output voltage and inductance are all
fixed, so to calculate the compensation voltage at
the boundary between DCM and CCM
(VCritical_COMP), use the following equation:
Where L1 is the inductor value and RESR is the
equivalent series resistance (ESR) value of the
output capacitor.
For ceramic capacitors, the capacitance
dominates the impedance at the switching
frequency and is the primary source of the output
voltage ripple. For simplification, estimate the
output voltage ripple with:
V V V
O
O
IN
Ipeak _ Critical
VOUT
VOUT
V L f OSC
IN
ΔVOUT
1
8 fS2 L1 C2
V
IN
Ipeak
VCritical_ COMP
Vslope V
is
For tantalum or electrolytic capacitors, the ESR
dominates the impedance at the switching
frequency. For simplification, estimate the output
ripple as:
GCS
Where GCS=3.2A/V, Vis=0.21V, and Vslope=D. D is
the duty cycle.
If VAAM exceeds VCritical_COMP, the convertor moves
from AAM to CCM directly and eliminates DCM.
This setting improves light-load efficiency.
However, the output ripple increases during light-
load. The inductor peak current at the transition
point is:
VOUT
VOUT
ΔVOUT
1
RESR
fS L1
V
IN
The characteristics of the output capacitor also
affect the stability of the regulation system. The
MP28266 can be optimized for a wide range of
capacitance and ESR values.
Ipeak VAAM V Vslope G
is
CS
Setting the AAM Voltage
If VAAM is lower than VCritical_COMP, the convertor
has three operating modes in the full load range.
As the gap between VAAM and VCritical_COMP
narrows, so does the DCM range. To improve
efficiency while retaining a reasonable ripple, set
VAAM close to VCritical_COMP. The inductor peak
current at this transition point is:
The AAM voltage sets the transition point from
AAM to CCM. Select a value that balances
efficiency, stability, ripple, and transient
response: A low AAM voltage improves stability
and ripple, but degrades AAM Mode efficiency
and transient response; Conversely, a high AAM
voltage improves AAM efficiency and transient
response, but degrades stability and ripple.
V
V G V V
is O
AAM
CS
IN
Ipeak
V VO L fOSC GCS
IN
Set the AAM voltage using a resistor divider as
shown in Figure 4.
MP28266 Rev. 1.0
3/16/2012
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11
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
Refer to Figure 5 to select an optimal voltage and
then use the following equation to determine the
value of R4. Assume R3 to be 10kꢀ:
The external BST diode connects from the VCC
pin to the BST pin, as shown in Figure 6.
External BST Diode
IN4148
BST
VCC
VCC
AAM
CBST
R4 R3
1
MP28266
SW
+
COUT
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
L
V
=5V
V
=2.5V
OUT
OUT
V
=3.3V
OUT
Figure 6: Optional External Bootstrap Diode
for Enhanced Efficiency
The recommended external BST diode is
IN4148, and the BST capacitor is 0.1µF to 1μF.
V
=1.2V
OUT
V
=1.8V
OUT
PC Board Layout
Place the high current paths (GND, IN and SW)
very close to the device with short, direct, and
wide traces. Place the input capacitor as close as
possible to the IN and GND pins. Place the
external feedback resistors next to the FB pin.
Keep the switching node SW short and away
from the feedback network.
0 1 2 3 4 5 6
7 8 9 10 1112
Figure 5: AAM Selection for Common Output
Voltages (VIN=6V-to-21V)
External Bootstrap Diode
An external bootstrap diode can enhance the
efficiency of the regulator given the applicable
conditions:
VOUT is 5V or 3.3V; and
VOUT
Duty cycle is high: D=
>65%
VIN
MP28266 Rev. 1.0
3/16/2012
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© 2012 MPS. All Rights Reserved.
12
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
TYPICAL APPLICATION CIRCUIT
U1
R5
20
1
6
IN
BST
SW
VIN
C1B
0.1
C1A
22
L1
2.8
C3
0.1
SW
F
F
F
H
MP28266
1.2V/3A
2,3,4,5
11
VCC
VOUT
GND
VCC
C2A
22
C2B
22
C2C
0.1
C6
C4
R6
F
F
F
R4
90.9k
15pF
0
0.1
F
GND
AAM
FB
7
9
8
AAM
FB
SS
C5
1
R8
24k
R1
10k
R7
10
R3
10k
F
R9
100k
10
SYNC
R2
10k
C7
47nF
SYNC
SS
Figure 7: Typical Application Circuit
MP28266 Rev. 1.0
3/16/2012
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© 2012 MPS. All Rights Reserved.
13
MP28266 – 21V, 3A, 500kHz, SYNCHRONOUS, STEP-DOWN CONVERTER
PACKAGE INFORMATION
QFN14 (3×4mm)
1.60
1.80
2.90
3.10
0.30
0.50
PIN 1 ID
SEE DETAIL A
PIN 1 ID
MARKING
1
14
0.18
0.30
3.20
3.40
3.90
4.10
PIN 1 ID
INDEX AREA
0.50
BSC
7
8
TOP VIEW
BOTTOM VIEW
PIN 1 ID OPTION A
0.30x45º TYP.
PIN 1 ID OPTION B
R0.20 TYP.
0.80
1.00
0.20 REF
0.00
0.05
SIDE VIEW
DETAIL A
2.90
1.70
NOTE:
0.70
1) ALL DIMENSIONS ARE IN MILLIMETERS.
2) EXPOSED PADDLE SIZE DOES NOT INCLUDE MOLD FLASH.
3) LEAD COPLANARITY SHALL BE 0.10 MILLIMETER MAX.
4) JEDEC REFERENCE IS MO-229, VARIATION VGED-3.
5) DRAWING IS NOT TO SCALE.
0.25
3.30
0.50
RECOMMENDED LAND PATTERN
NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications.
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.
MP28266 Rev. 1.0
3/16/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
14
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