MP1474 [MPS]
High-Efficiency, 2A, 16V, 500kHz Synchronous, Step-Down Converter; 高效率， 2A ， 16V ， 500kHz的同步，降压转换器
| 型号： | MP1474 |
| 厂家： | 
MONOLITHIC POWER SYSTEMS |
| 描述： | High-Efficiency, 2A, 16V, 500kHz Synchronous, Step-Down Converter |
| 文件： | 总16页 (文件大小：462K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MP1474
High-Efficiency, 2A, 16V, 500kHz
Synchronous, Step-Down Converter
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP1474 is a high-frequency, synchronous,
rectified, step-down, switch-mode converter
with built-in power MOSFETs. It offers a very
compact solution to achieve a 2A continuous
output current with excellent load and line
regulation over a wide input supply range. The
MP1474 has synchronous mode operation for
higher efficiency over the output current load
range.
Wide 4.5V-to-16V Operating Input Range
100mΩ/40mΩ Low RDS(ON) Internal Power
MOSFETs
High-Efficiency Synchronous Mode
Operation
Fixed 500kHz Switching Frequency
Synchronizes from a 200kHz-to-2MHz
External Clock
Power-Save Mode at Light Load
Internal Soft-Start
Power Good Indicator
OCP Protection and Hiccup
Thermal Shutdown
Output Adjustable from 0.8V
Available in an 8-pin TSOT-23 Package
Current-mode operation provides fast transient
response and eases loop stabilization.
Full protection features include over-current
protection and thermal shut down.
The MP1474 requires a minimal number of
readily-available standard external components,
and is available in a space-saving 8-pin
TSOT23 package.
APPLICATIONS
Notebook Systems and I/O Power
Digital Set-Top Boxes
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 Quality Assurance. “MPS” and “The
Future of Analog IC Technology” are Registered Trademarks of Monolithic
Power Systems, Inc.
TYPICAL APPLICATION
Efficiency vs.
Output Current
R3
20
4.5V-16V
5
2
V
=3.3V, I =0.01A-2A
VIN
IN
BST
SW
OUT
OUT
100
95
90
85
80
75
70
65
60
55
50
C1
22
C4
MP1474
3.3V/2A
3
V
=5V
IN
6
7
1
EN/SYNC
L1
V
=12V
IN
C2
47
EN/
R1
SYNC
R6
16k
V
=16V
40.2k
IN
VCC
8
FB
R5
100k
C5
0.1
R2
13k
PG
GND
4
0.0
0.4
0.8
1.2
1.6
2.0
OUTPUT CURRENT (A)
MP1474 Rev. 1.0
9/26/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
1
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
ORDERING INFORMATION
Part Number*
Package
Top Marking
MP1474DJ
TSOT-23-8
ADK
* For Tape & Reel, add suffix –Z (e.g. MP1474DJ–Z);
For RoHS Compliant Packaging, add suffix –LF (e.g. MP1474DJ–LF–Z)
PACKAGE REFERENCE
TOP VIEW
PG
IN
FB
1
2
3
4
8
7
6
5
VCC
SW
GND
EN/SYNC
BST
ABSOLUTE MAXIMUM RATINGS (1)
VIN ..................................................-0.3V to 17V
Thermal Resistance (5)
TSOT-23-8.............................100..... 55... °C/W
θJA
θJC
V
SW......................................................................
-0.3V (-5V for <10ns) to 17V (19V for <10ns)
BST ........................................................ VSW+6V
Notes:
1) Exceeding these ratings may damage the device.
2) About the details of EN pin’s ABS MAX rating, please refer to
Page 9, Enable/SYNC control section.
V
All Other Pins................................ -0.3V to 6V (2)
3) 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.
(3)
Continuous Power Dissipation (TA = +25°C)
........................................................... 1.25W
Junction Temperature...............................150°C
Lead Temperature ....................................260°C
Storage Temperature................. -65°C to 150°C
Recommended Operating Conditions (4)
Supply Voltage VIN ...........................4.5V to 16V
Output Voltage VOUT.....................0.8V to VIN-3V
Operating Junction Temp. (TJ). -40°C to +125°C
4) The device is not guaranteed to function outside of its
operating conditions.
5) Measured on JESD51-7, 4-layer PCB.
MP1474 Rev. 1.0
9/26/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
2
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
ELECTRICAL CHARACTERISTICS (6)
VIN = 12V, TA = 25°C, unless otherwise noted.
Parameter
Symbol Condition
Min
Typ
7
Max
Units
μA
Supply Current (Shutdown)
Supply Current (Quiescent)
HS Switch-On Resistance
LS Switch-On Resistance
Switch Leakage
IIN
Iq
VEN = 0V
VEN = 2V, VFB = 1V
0.6
100
40
1
mA
mΩ
mΩ
μA
HSRDS-ON VBST-SW=5V
LSRDS-ON VCC =5V
SWLKG VEN = 0V, VSW =12V
1
Current Limit (6)
ILIMIT
fSW
Under 40% Duty Cycle
VFB=0.75V
3
A
Oscillator Frequency
Fold-Back Frequency
Maximum Duty Cycle
Minimum On Time(6)
Sync Frequency Range
430
500
0.25
95
570
kHz
fSW
fFB
VFB<400mV
DMAX
τON MIN
fSYNC
VFB=700mV
90
%
40
ns
0.2
791
787
2
MHz
TA =25°C
-40°C<TA<85°C (7)
807
807
10
823
827
50
Feedback Voltage
VFB
mV
Feedback Current
IFB
VFB=820mV
nA
V
EN Rising Threshold
EN Falling Threshold
VEN RISING
VEN FALLING
1.2
1.1
1.4
1.6
1.4
1.25
V
VEN=2V
VEN=0
2
0
μA
μA
EN Input Current
IEN
EN Turn-Off Delay
ENtd-off
PGvth-Hi
PGvth-Lo
PGTd
5
μs
VFB
VFB
ms
Power-Good Rising Threshold
Power-Good Falling Threshold
Power-Good Delay
0.9
0.85
0.4
Power-Good Sink Current
Capability
VPG
Sink 4mA
0.4
1
V
μA
V
Power-Good Leakage Current
IPG-LEAK
INUVVth
VIN Under-Voltage Lockout
Threshold—Rising
3.7
3.9
4.1
VIN Under-Voltage Lockout
Threshold—Hysteresis
INUVHYS
VCC
650
mV
VCC Regulator
5
3
V
%
VCC Load Regulation
ICC=5mA
Soft-Start Period
τSS
1.2
150
20
ms
°C
°C
Thermal Shutdown (6)
Thermal Hysteresis (6)
Notes:
6) Guaranteed by design.
7) Not tested in production and guaranteed by over-temperature correlation.
MP1474 Rev. 1.0
9/26/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
3
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
TYPICAL CHARACTERISTICS
VIN = 12V, VOUT = 3.3V, L=5.5μH, TA = 25°C, unless otherwise noted.
Peak Current
vs. Duty Cycle
Load Regulation Line Regulation
V
=5-16V, I
=0-2A
V =5V-16V
IN
IN OUT
0.5
0.3
4.3
4
0.3
I
=0A
OUT
0.2
0.1
0
V
=12V
IN
V
=16V
IN
3.7
3.4
3.1
2.8
2.5
0.1
I
=1A
OUT
-0.1
-0.3
-0.5
V
=5V
IN
-0.1
-0.2
-0.3
I
=2A
OUT
0
0.4
0.8
1.2
1.6
2
5
6
7
8
9 10 11 12 13 14 15 16
25 30 35 40 45 50 55 60 65 70 75
OUTPUT CURRENT (A)
INPUT VOLTAGE(V)
Disabled Supply Current
vs. Input Voltage
Enabled Supply Current
vs. Input Voltage
V =1V
FB
V
=0V
EN
20
800
750
700
650
600
550
500
450
400
17
14
11
8
5
2
-1
-4
-7
-10
0
5
10
15
20
4
6
8
10 12 14 16 18
INPUT VOLTAGE(V)
INPUT VOLTAGE(V)
MP1474 Rev. 1.0
9/26/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
4
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS
Performance waveforms are tested on the evaluation board of the Design Example section.
VIN = 12V, VOUT = 3.3V, L=5.5μH, TA = 25°C, unless otherwise noted.
100
95
90
85
80
75
70
65
60
55
50
100
95
90
85
80
75
70
65
60
55
50
100
95
90
85
80
75
70
65
60
55
50
V
=5V
V
=5V
IN
IN
V
=12V
V
=5V
IN
IN
V
=12V
IN
V
=12V
IN
V
=16V
IN
V
=16V
IN
V
=16V
IN
0.0
0.4
0.8
1.2
1.6
2.0
0.0
0.4
0.8
1.2
1.6
2.0
0.0
0.4
0.8
1.2
1.6
2.0
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Case Temperature Rise
vs. Output Current
I
=0A-2A
OUT
100
95
90
85
80
75
70
65
60
55
50
100
95
90
85
80
75
70
65
60
55
50
18
15
12
9
V
=7V
V
=5V
IN
IN
V
=12V
IN
V
=12V
IN
V
=16V
IN
V
=16V
IN
6
3
0
0.0
0.4
0.8
1.2
1.6
2.0
0.0
0.4
0.8
1.2
1.6
2.0
0
0.5
1
1.5
2
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Short Entry
Short Recovery
Startup through Enable
I
=0A
I
=0A
I
=0A
OUT
OUT
OUT
V
OUT
V
V
OUT
OUT
2V/div.
V
5V/div.
2V/div.
V
5V/div.
2V/div.
V
5V/div.
PG
PG
PG
V
IN
V
V
EN
IN
10V/div.
5V/div.
10V/div.
V
SW
V
V
SW
SW
10V/div.
10V/div.
10V/div.
I
INDUCTOR
5A/div.
I
I
INDUCTOR
2A/div.
INDUCTOR
5A/div.
MP1474 Rev. 1.0
9/26/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
5
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Performance waveforms are tested on the evaluation board of the Design Example section.
VIN = 12V, VOUT = 3.3V, L=5.5μH, TA = 25°C, unless otherwise noted.
Startup through Enable
Shutdown through
Enable
Shutdown through
Enable
I
=2A
OUT
I
=0A
I
=2A
OUT
OUT
V
V
OUT
V
OUT
OUT
2V/div.
2V/div.
2V/div.
V
V
PG
V
PG
PG
5V/div.
5V/div.
5V/div.
V
V
EN
V
EN
EN
5V/div.
5V/div.
5V/div.
V
V
SW
V
SW
SW
10V/div.
10V/div.
10V/div.
I
I
INDUCTOR
2A/div.
I
INDUCTOR
2A/div.
INDUCTOR
2A/div.
Startup through Input
Voltage
Startup through Input
Voltage
Shutdown through
Input Voltage
I
=0A
I
=2A
I
=0A
OUT
OUT
OUT
V
V
OUT
V
OUT
OUT
2V/div.
2V/div.
2V/div.
V
V
PG
V
PG
PG
5V/div.
5V/div.
5V/div.
V
V
IN
V
IN
IN
5V/div.
5V/div.
5V/div.
V
V
SW
V
SW
SW
5V/div.
5V/div.
5V/div.
I
I
INDUCTOR
2A/div.
I
INDUCTOR
2A/div.
INDUCTOR
2A/div.
Shutdown through
Input Voltage
Input / Output Ripple
Load Transient Reponse
I
=2A
I
=1A-2A
OUT
OUT
I
=2A
OUT
V
/AC
OUT
V
20mV/div.
OUT
2V/div.
V
V
/AC
PG
OUT
V
AC
IN/
5V/div.
50mV/div.
200mV/div.
V
IN
5V/div.
V
SW
V
SW
10V/div.
5V/div.
I
OUT
I
L
1A/div.
I
INDUCTOR
2A/div.
2A/div.
MP1474 Rev. 1.0
9/26/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
6
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
PIN FUNCTIONS
Package
Pin #
Name Description
Power Good Output. The output of this pin is an open drain that goes high if the output
voltage exceeds 90% of the normal voltage. There is a 0.4ms delay between when
FB≥90% to when the PG pin goes high.
1
PG
IN
Supply Voltage. The IN pin supplies power for internal MOSFET and regulator. The
MP1474 operates from a +4.5V to +16V input rail. Requires a low-ESR, and low-
inductance capacitor (C1) to decouple the input rail. Place the input capacitor very close to
this pin and connect it with wide PCB traces and multiple vias.
2
3
Switch Output. Connect to the inductor and bootstrap capacitor. This pin is driven up to VIN
by the high-side switch during the PWM duty cycle ON time. The inductor current drives
the SW pin negative during the OFF time. The ON resistance of the low-side switch and
the internal body diode fixes the negative voltage. Connect using wide PCB traces and
multiple vias.
SW
System Ground. Reference ground of the regulated output voltage. PCB layout Requires
extra care. For best results, connect to GND with copper and vias.
4
5
6
7
GND
BST
Bootstrap. Requires a capacitor connected between SW and BST pins to form a floating
supply across the high-side switch driver.
Enable. EN=high to enable the MP1474. Apply an external clock change the switching
frequency. For automatic start-up, connect EN pin to VIN with a 100kꢀ resistor.
EN/SYNC
VCC
Internal 5V LDO output. Powers the driver and control circuits. Decouple with 0.1μF-to-
0.22μF capacitor. Do not use a capacitor ≥0.22μF.
Feedback. Connect to the tap of an external resistor divider from the output to GND to set
the output voltage. The frequency fold-back comparator lowers the oscillator frequency
when the FB voltage is below 400mV to prevent current limit runaway during a short circuit
fault. Place the resistor divider as close to the FB pin as possible. Avoid placing vias on
the FB traces.
8
FB
MP1474 Rev. 1.0
9/26/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
7
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
FUNCTIONAL BLOCK DIAGRAM
IN
+
-
VCC
Regulator
RSEN
Currrent Sense
VCC
Amplifer
Bootstrap
Regulator
BST
Oscillator
HS
Driver
+
-
SW
Comparator
On Time Control
Logic Control
1pF
VCC
Current Limit
Comparator
50pF
400k
Reference
EN/SYNC
LS
Driver
1MEG
6.5V
+
+
-
FB
GND
-
Error Amplifier
PG
+
Ref
Figure 1: Functional Block Diagram
MP1474 Rev. 1.0
9/26/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
8
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
OPERATION
The MP1474 is a high-frequency, synchronous,
rectified, step-down, switch-mode converter
with built-in power MOSFETs. It offers a very
compact solution that achieves a 2A continuous
output current with excellent load and line
regulation over a wide input supply range.
The EN pin is clamped internally using a 6.5V
series-Zener-diode as shown in Figure 2.
Connecting the EN input pin through a pullup
resistor to the voltage on the IN pin limits the
EN input current to less than 100µA.
For example, with 12V connected to IN, RPULLUP
≥ (12V – 6.5V) ÷ 100µA = 55kꢀ.
The MP1474 operates in a fixed-frequency,
peak-current–control mode to regulate the
output voltage. An internal clock initiates a
PWM cycle. The integrated high-side power
MOSFET turns on and remains on until the
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 95% of one PWM period, the current in
the power MOSFET does not reach the value
set by the COMP value, the power MOSFET is
forced off.
Connecting the EN pin is directly to a voltage
source without any pullup resistor requires
limiting the amplitude of the voltage source to
≤6V to prevent damage to the Zener diode.
Figure 2: 6.5V Zener Diode Connection
Internal Regulator
For external clock synchronization, connect a
clock with a frequency range between 200kHz
and 2MHz 2ms after the output voltage is set:
The internal clock rising edge will synchronize
with the external clock rising edge. Select an
external clock signal with a pulse width less
than 1.7μs.
A 5V internal regulator powers most of the
internal circuitries. This regulator takes VIN and
operates in the full VIN range. When VIN
exceeds 5.0V, the output of the regulator is in
full regulation. When VIN is less than 5.0V, the
output decreases, and the part requires a 0.1µF
ceramic decoupling capacitor.
Under-Voltage Lockout (UVLO)
Error Amplifier
The MP1474 has under-voltage lock-out
protection (UVLO). When the VCC voltage
exceeds the UVLO rising threshold voltage, the
MP1474 powers up. It shuts off when the VCC
voltage drops below the UVLO falling threshold
voltage. This is non-latch protection.
The error amplifier compares the FB pin voltage
to the internal 0.807V reference (VREF) and
outputs a current proportional to the difference
between the two. This output current then
charges
or
discharges
the
internal
compensation network to form 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.
The MP1474 is disabled when the input voltage
falls below 3.25V. If an application requires a
higher under-voltage lockout (UVLO) threshold,
use the EN pin as shown in Figure 3 to adjust
the input voltage UVLO by using two external
resistors. For best results, set the UVLO falling
threshold (VSTOP) above 4.5V using the
enable resistors. Set the rising threshold
(VSTART) to provide enough hysteresis to
allow for any input supply variations.
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. An
internal 1Mꢀ resistor from EN/SYNC to GND
allows EN/SYNC to be floated to shut down the
chip.
MP1474 Rev. 1.0
9/26/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
9
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
Thermal Shutdown
Thermal shutdown prevents the chip from
operating at exceedingly high temperatures.
When the silicon die reaches temperatures that
exceed 150°C, it shuts down the whole chip.
When the temperature drops below its lower
threshold, typically 130°C, the chip is enabled
again.
Floating Driver and Bootstrap Charging
An external bootstrap capacitor powers the
floating power MOSFET driver. This floating
Figure 3: Adjustable UVLO
Internal Soft-Start
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, M1, R3, C4, L1 and C2 (Figure 4). If (VIN-
VSW) exceeds 5V, U1 will regulate M1 to
maintain a 5V BST voltage across C4. A 20ꢀ
resistor placed between SW and BST cap. is
strongly recommended to reduce SW spike
voltage.
The soft-start prevents the converter output
voltage from overshooting during startup. When
the chip starts, the internal circuitry generates a
soft-start voltage (VSS) that ramps up from 0V to
1.2V. When VSS is less than VREF, the error
amplifier uses VSS as the reference. When VSS
exceeds VREF, the error amplifier uses VREF as
the reference. The SS time is internally set to
1.2ms.
Power Good Indicator
D1
MP1474 has an open drain pin as the power-
good indicator (PG). Pull this up to VCC or
another external source through a 100kꢀ
resistor. When VFB exceeds 90% of VREF, PG
switches goes high with 0.4ms delay time. If VFB
goes below 85% of VREF, an internal MOSFET
pulls the PG pin down to ground.
VIN
M1
BST
U1
R3
5V
C4
VOUT
C2
L1
SW
The internal circuit keeps the PG low once the
input supply exceeds 1.2V.
Figure 4: Internal Bootstrap Charging Circuit
Over-Current-Protection and Hiccup
The MP1474 has a cycle-by-cycle over-current
limit when the inductor current peak value
exceeds the set current limit threshold.
Meanwhile, the output voltage drops until VFB is
below the Under-Voltage (UV) threshold—
typically 50% below the reference. Once UV is
triggered, the MP1474 enters hiccup mode to
periodically restart the part. This protection
mode is especially useful when the output is
dead-shorted to ground, and greatly reduces
the average short circuit current to alleviate
thermal issues and protect the regulator. The
MP1474 exits the hiccup mode once the over-
current condition is removed.
Startup and Shutdown
If both VIN and VEN exceed their respective
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 a stable supply
for the remaining circuitries.
Three events can shut down the chip: VEN low,
VIN low, and thermal shutdown. During 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.
MP1474 Rev. 1.0
9/26/2012
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2012 MPS. All Rights Reserved.
10
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
APPLICATION INFORMATION
Setting the Output Voltage
Where ΔIL is the inductor ripple current.
The external resistor divider sets 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 around 40kꢀ. R2 is then given by:
Choose the inductor ripple current to be
approximately 30% of the maximum load current.
The maximum inductor peak current is:
IL
IL(MAX) ILOAD
2
R1
Use a larger inductor for improved efficiency
under light-load conditions—below 100mA.
R2
V
OUT
1
Selecting the Input Capacitor
0.807V
The input current to the step-down converter is
discontinuous, therefore requires a capacitor is to
supply the AC current to the step-down converter
while maintaining the DC input voltage. Use low
ESR capacitors for the best performance. Use
ceramic capacitors with X5R or X7R dielectrics
for best results because of their low ESR and
small temperature coefficients. For most
applications, use a 22µF capacitor.
The T-type network—as shown in Figure 5—is
highly recommended when VOUT is low.
Cf
R1
Rt
8
FB
VOUT
R2
Since C1 absorbs the input switching current, it
requires an adequate ripple current rating. The
RMS current in the input capacitor can be
estimated by:
Figure 5: 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
VIN
VOUT
VIN
IC1 ILOAD
1
VOUT
(V)
R1 (kΩ) R2 (kΩ) Rt (kΩ) Cf(pF) L(μH)
The worse case condition occurs at VIN = 2VOUT
,
where:
1.0
1.2
1.8
2.5
3.3
5
20.5
30.1
40.2
40.2
40.2
40.2
84.5
61.9
32.4
19.1
13
82
82
33
33
16
16
15
15
15
15
15
15
2.2
2.2
4.7
4.7
5.5
5.5
ILOAD
IC1
2
For simplification, choose an input capacitor with
an RMS current rating greater than half of the
maximum load current.
7.68
The input capacitor can be electrolytic, tantalum
or ceramic. When using electrolytic or tantalum
capacitors, add a small, high quality ceramic
capacitor (e.g. 0.1μF) 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 as:
Selecting the Inductor
Use a1µH-to-10µH inductor with a DC current
rating of at least 25% percent higher than the
maximum load current for most applications. For
highest efficiency, use an inductor with a DC
resistance less than 15mꢀ. For most designs,
the inductance value can be derived from the
following equation.
ILOAD
VOUT
VOUT
VOUT (V VOUT
)
IN
V
1
IN
L1
fS C1
V
IN
V
IN
V IL fOSC
IN
MP1474 Rev. 1.0
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11
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
External Bootstrap Diode
Selecting the Output Capacitor
The output capacitor (C2) maintains the DC
output voltage. Use ceramic, tantalum, or low-
ESR electrolytic capacitors. For best results,
use low ESR capacitors to keep the output
voltage ripple low. The output voltage ripple can
be estimated as:
An external bootstrap diode can enhance the
efficiency of the regulator given the following
conditions:
VOUT is 5V or 3.3V; and
VOUT
Duty cycle is high: D=
>65%
VIN
VOUT
VOUT
1
In these cases, add an external BST diode from
the VCC pin to BST pin, as shown in Figure 6.
VOUT
1
R
ESR
fS L1
V
8 fS C2
IN
External BST Diode
IN4148
Where L1 is the inductor value and RESR is the
equivalent series resistance (ESR) value of the
output capacitor.
BST
VCC
CBST
MP1474
SW
For ceramic capacitors, the capacitance
dominates the impedance at the switching
frequency, and the capacitance causes the
majority of the output voltage ripple. For
simplification, the output voltage ripple can be
estimated as:
L
COUT
Figure 6: Optional External Bootstrap Diode to
Enhance Efficiency
The recommended external BST diode is
IN4148, and the BST capacitor value is 0.1µF
to 1μF.
VOUT
8 fS2 L1 C2
VOUT
ΔVOUT
1
V
IN
For tantalum or electrolytic capacitors, the ESR
dominates the impedance at the switching
frequency. For simplification, the output ripple
can be approximated as:
VOUT
VOUT
ΔVOUT
1
RESR
fS L1
V
IN
The characteristics of the output capacitor also
affect the stability of the regulation system. The
MP1474 can be optimized for a wide range of
capacitance and ESR values.
MP1474 Rev. 1.0
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12
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
PC Board Layout (8)
PCB layout is very important to achieve stable
operation especially for VCC capacitor and
input capacitor placement. For best results,
follow these guidelines:
1. Use large ground plane directly connect to
GND pin. Add vias near the GND pin if
bottom layer is ground plane.
2. Place the VCC capacitor to VCC pin and
GND pin as close as possible. Make the
trace length of VCC pin-VCC capacitor
anode-VCC capacitor cathode-chip GND
pin as short as possible.
3. Place the ceramic input capacitor close to
IN and GND pins. Keep the connection of
input capacitor and IN pin as short and
wide as possible.
Design Example
Below is a design example following the
application guidelines for the specifications:
4. Route SW, BST away from sensitive
analog areas such as FB. It’s not
recommended to route SW, BST trace
under chip’s bottom side.
Table 2: Design Example
VIN
VOUT
Io
12V
3.3V
2A
5. Place the T-type feedback resistor R6 close
to chip to ensure the trace which connects
to FB pin as short as possible
Notes:
The detailed application schematic is shown in
Figure 8. The typical performance and circuit
waveforms have been shown in the Typical
Performance Characteristics section. For more
device applications, please refer to the related
Evaluation Board Datasheets.
8) The recommended layout is based on the Figure 7 Typical
Application circuit on the next page.
MP1474 Rev. 1.0
9/26/2012
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13
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
TYPICAL APPLICATION CIRCUITS
R3
20
2
5
VIN
BST
IN
C1
0.1uF
25V
C1A
22uF
25V
C4
0.1uF
MP1474
L1
GND
GND
5.5uH
VOUT
VOUT
VOUT
5V/2A
C2A
7
1
6
3
VCC
PG
VCC
PG
SW
C5
0.1uF
C2
22uF
22uF
R5
100k
GND
GND
GND
C3
15pF
R4
100k
R6
16k
8
EN/SYNC
FB
EN/SYNC
R1
GND
GND
40.2k
R2
7.68k
GND
Figure 7: 12VIN, 5V/2A Output
R3
20
2
5
VIN
VCC
BST
IN
C1
C1A
22uF
25V
C4
0.1uF
0.1uF
25V
MP1474
L1
5.5uH
GND
GND
3.3V/2A
C2A
7
1
6
3
VCC
PG
SW
C5
0.1uF
C2
22uF
22uF
R5
100k
GND
GND
GND
PG
C3
15pF
R4
100k
R6
16k
8
EN/SYNC
FB
EN/SYNC
R1
GND
GND
40.2k
R2
13k
GND
Figure 8: 12VIN, 3.3V/2A Output
R3
20
2
5
VIN
VCC
BST
IN
C1
C1A
22uF
25V
C4
0.1uF
0.1uF
25V
MP1474
L1
4.7uH
GND
GND
2.5V/2A
C2A
7
3
VCC
PG
SW
C5
0.1uF
C2
22uF
22uF
R5
100k
GND
GND
GND
1
6
PG
C3
15pF
R4
100k
R6
33k
8
EN/SYNC
FB
EN/SYNC
R1
40.2k
GND
GND
R2
19.1k
GND
Figure 9: 12VIN, 2.5V/2A Output
MP1474 Rev. 1.0
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14
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER
R3
20
2
7
1
6
5
VIN
VCC
BST
IN
C1
C1A
22uF
25V
C4
0.1uF
25V
0.1uF
MP1474
L1
GND
GND
4.7uH
VOUT
1.8V/2A
C2A
3
VCC
PG
SW
C5
0.1uF
C2
22uF
22uF
R5
100k
GND
GND
GND
PG
C3
15pF
R4
100k
R6
33k
8
EN/SYNC
FB
EN/SYNC
R1
40.2k
GND
GND
R2
32.4k
GND
Figure 10: 12VIN, 1.8V/2A Output
R3
20
2
5
VIN
VCC
BST
IN
C1
C1A
22uF
25V
C4
0.1uF
25V
0.1uF
MP1474
L1
GND
GND
2.2uH
VOUT
1.2V/2A
7
1
6
3
VCC
PG
SW
C5
0.1uF
C2
22uF
C2A
22uF
R5
100k
GND
GND
GND
PG
C3
15pF
R4
100k
R6
82k
8
EN/SYNC
FB
EN/SYNC
R1
30.1k
GND
GND
R2
61.9k
GND
Figure 11: 12VIN, 1.2V/2A Output
R3
20
2
7
1
6
5
VIN
VCC
BST
IN
C1
C1A
22uF
25V
C4
0.1uF
25V
0.1uF
MP1474
L1
GND
GND
2.2uH
VOUT
1V/2A
3
VCC
PG
SW
C5
0.1uF
C2
22uF
C2A
22uF
R5
100k
GND
GND
GND
PG
C3
15pF
R4
100k
R6
82k
8
EN/SYNC
FB
EN/SYNC
R1
20.5k
GND
GND
R2
84.5k
GND
Figure 12: 12VIN, 1V/2A Output
MP1474 Rev. 1.0
9/26/2012
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15
MP1474 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
PACKAGE INFORMATION
TSOT23-8
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.
MP1474 Rev. 1.0
9/26/2012
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16
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