MP2451DT-Z [MPS]
Switching Regulator, Current-mode, 0.85A, 2400kHz Switching Freq-Max, PDSO6, MO-193AB, SOT23, 6 PIN;
| 型号： | MP2451DT-Z |
| 厂家： | 
MONOLITHIC POWER SYSTEMS |
| 描述： | Switching Regulator, Current-mode, 0.85A, 2400kHz Switching Freq-Max, PDSO6, MO-193AB, SOT23, 6 PIN 开关 光电二极管 输出元件 |
| 文件： | 总14页 (文件大小：346K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MP2451
36V, 2MHz, 0.6A
Step-Down Converter
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP2451 is a high frequency (2MHz) step-
down switching regulator with integrated
internal high-side high voltage power MOSFET.
It provides single 0.6A (or less) highly efficient
output with current mode control for fast loop
response.
•
•
•
•
•
•
•
•
130μA Operating Quiescent Current
Wide 3.3V to 36V Operating Input Range
500mΩ Internal Power MOSFET
2MHz fixed Switching Frequency
Internally compensated
Stable with Ceramic Output Capacitors
Internal Soft-Start
Precision Current Limit Without Current
Sensing Resistor
> 90% Efficiency
The wide 3.3V to 36V input range
accommodates
a
variety of step-down
applications in automotive input environment. A
3μA shutdown mode quiescent current allows
use in battery-powered applications.
•
•
•
•
Output Adjustable from +0.8V to 0.8xVIN
3μA Low Shutdown Supply Current
6-Lead SOT23 Package
High power conversion efficiency over a wide
load range is achieved by scaling down the
switching frequency at light load condition to
reduce the switching and gate driving losses.
APPLICATIONS
•
•
•
•
•
High Voltage Power Conversion
Automotive Systems
Industrial Power Systems
Distributed Power Systems
Battery Powered Systems
Frequency fold-back helps prevent inductor
current runaway during start-up. Thermal
shutdown provides reliable, fault-tolerant
operation.
The MP2451 is available in the cost-effective
SOT23-6L 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
Efficiency
V
OUT=5V
95
90
85
80
75
70
VIN=8V
C4
L1
VOUT
5V/0.6A
100nF
6
1
SW
BST
VIN=24V
VIN=36V
VIN=12V
D1
MP2451
VIN
C1
5
4
GND
VIN
EN
65
60
55
3
FB
Control
C3
33pF
50
0
0.1 0.2 0.3 0.4 0.5 0.6
OUTPUT CURRENT(A)
MP2451 Rev. 1.32
3/20/2014
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2014 MPS. All Rights Reserved.
1
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
ORDERING INFORMATION
Part Number*
MP2451DT
Package
SOT23-6L
Top Marking
V7
* For Tape & Reel, add suffix –Z (e.g. MP2451DT–Z)
For RoHS Compliant Packaging, add suffix –LF (e.g. MP2451DT–LF–Z)
PACKAGE REFERENCE
TOP VIEW
BST
GND
FB
1
2
3
6
5
4
SW
VIN
EN
ABSOLUTE MAXIMUM RATINGS (1)
Supply Voltage (VIN)........................-0.3V to 40V
Switch Voltage (VSW)...... -0.3V to VIN (MAX) + 0.3V
BST to SW.......................................-0.3 to 6.0V
Enable (VEN)................................................... 8V
Enable Sink Current (IEN) ......................... 100μA
All Other Pins.................................-0.3V to 5.0V
Thermal Resistance (4)
SOT23-6L..............................220.... 110.. °C/W
θJA
θJC
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.
(2)
Continuous Power Dissipation (TA=+25°C)
........................................................... 0.57W
Junction Temperature...............................150°C
Lead Temperature ....................................260°C
Storage Temperature................. -65°C to 150°C
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 ...........................3.3V to 36V
Output Voltage VOUT.................. +0.8V to 0.8*VIN
Operating Junction Temp. (TJ). -40°C to +125°C
MP2451 Rev. 1.32
3/20/2014
www.MonolithicPower.com
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2
© 2014 MPS. All Rights Reserved.
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
ELECTRICAL CHARACTERISTICS
VIN = 12V, VEN = 2V, TA= 25°C, unless otherwise noted.
Parameter
Condition
Min
Typ
0.794
0.794
500
Max
0.810
0.818
Units
V
Feedback Voltage
4.0V < VIN < 36V
3.3V < VIN < 4.0V
VBST-VSW=5V
0.778
0.770
V
Upper Switch On Resistance
Upper Switch Leakage
Current Limit
mΩ
μA
A
VEN = 0V, VSW = 0V
0.1
1
1.0
COMP to Current Sense
Transconductance
GCS
3
A/V
Minimum Operating VIN Voltage
VIN UVLO Up Threshold
VIN UVLO Hysteresis
3.3
2.7
V
V
3.2
0.4
0.5
V
Soft-start time
FB from 0 to 1.8V
VEN = 0V
msec
kHz
ns
μA
uA
°C
V
Oscillator Frequency
1600
1.4
2000
100
3
2400
15
Minimum Switch On Time
Shutdown Supply Current
Average Quiescent Supply Current No load, VFB=0.9
Thermal Shutdown
130
150
1.55
0.3
Enable up Threshold
1.7
Enable Threshold Hysteresis
Enable Clamping Voltage
V
7.5
V
PIN FUNCTIONS
Pin #
Name
Description
Bootstrap. This is the positive power supply for the internal floating high side MOSFET
driver. Connect a bypass capacitor between this pin and SW pin.
1
BST
Ground. It should be connected as close as possible to the output capacitor avoiding
the high current switch paths.
2
3
4
5
6
GND
FB
Feedback. This is the input to the error amplifier. An external resistive divider
connected between the output and GND is compared to the internal +0.8V reference
to set the regulation voltage.
Enable input. Pulling this pin below the specified threshold shuts the chip down. Pulling
it above the specified threshold enables the chip. Floating this pin shuts the chip down.
EN
Input Supply. This supplies power to all the internal control circuitry, both BS regulators
and the high side switch. A decoupling capacitor to ground is required close to this pin
to reduce switching spikes.
VIN
SW
Switch node. This is the output from the high-side switch. A low VF Schottky diode to
ground is required close to this pin to reduce switching spikes.
MP2451 Rev. 1.32
3/20/2014
www.MonolithicPower.com
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© 2014 MPS. All Rights Reserved.
3
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, C1 = 4.7µF, C2 = 10µF, L = 3.3µH and TA = +25°C, unless otherwise noted.
Efficiency
Efficiency
V
OUT=2.5V
V
OUT=3.3V
90
85
80
75
70
65
60
90
85
80
75
70
65
60
V
IN=6V
V
IN=8V
V
IN=12V
VIN=12V
V
IN=24V
0
0.1 0.2 0.3 0.4 0.5 0.6
OUTPUT CURRENT(A)
0
0.1 0.2 0.3 0.4 0.5 0.6
OUTPUT CURRENT(A)
Steady State
Startup Through EN
Steady State
V
IN=12V,VOUT=5V,IOUT=0.6A
V
IN=12V,VOUT=5V,IOUT=0.1A
V
IN=12V,VOUT=5V,IOUT=0.1A
V
OUT
V
OUT
(AC coupled)
(AC coupled)
V
OUT
10mV/div.
10mV/div.
5
V/div.
VEN
2V/div.
VSW
10V/div.
VSW
10V/div.
VSW
10V/div.
IL
IL
500mA/div.
IL
500mA/div.
.
500mA/div
400ns/div.
400ns/div.
Shutdown Through EN
Shutdown Through EN
Startup Through EN
V
IN=12V,VOUT=5V,IOUT=0.1A
V
IN=12V,VOUT=5V,IOUT=0.6A
V
IN=12V,VOUT=5V,IOUT=0.6A
V
OUT
V
OUT
V
OUT
5V/div.
5V/div.
5
V/div.
VEN
2V/div.
VEN
2V/div.
VEN
2V/div.
VSW
VSW
10V/div.
VSW
10V/div.
10V/div.
IL
IL
IL
500mA/div.
500mA/div.
500mA/div.
.
2ms/div.
MP2451 Rev. 1.32
3/20/2014
www.MonolithicPower.com
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© 2014 MPS. All Rights Reserved.
4
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VIN = 12V, C1 = 4.7µF, C2 = 10µF, L = 3.3µH and TA = +25°C, unless otherwise noted.
Short Circuit Entry
Short Circuit Recovery
I
OUT=0A to Short
I
OUT= Short to 0A
VOUT
VOUT
2V/div.
2V/div.
IL
IL
500mA/div
500mA/div
MP2451 Rev. 1.32
3/20/2014
www.MonolithicPower.com
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© 2014 MPS. All Rights Reserved.
5
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
FUNCTION BLOCK DIAGRAM
VIN
INTERNAL
REGULATOR
REFERENCE
UVLO
EN
BST
ISW
-
LOGIC
+
GND
SS
0.5ms SS
ISW
SW
--
COMP
FB
SS
0.8V
+
OSCILATOR
2MHz
Figure 1—Function Block Diagram
OPERATION
The MP2451 is a 2MHz, non-synchronous, step-
down switching regulator with integrated internal
high-side high voltage power MOSFET. It
provides internally compensated single 0.6A
highly efficient output with current mode control.
It features wide input voltage range, internal soft-
start control, and precision current limit. Its very
low operational quiescent current suits it for
battery powered applications.
If, in one PWM period, the current in the power
MOSFET does not reach COMP set current
value, the power MOSFET remains on, saving a
turn-off operation.
Pulse Skipping Mode
At light load condition, the MP2451 goes into
pulse skipping mode to improve light load
efficiency. Pulse skipping decision is based on its
internal COMP voltage. If COMP is lower than
the internal sleep threshold, a PAUSE command
is generated to block the turn-on clock pulse so
the power MOSFET is not commanded ON
subsequently, saving gate driving and switching
losses. This PAUSE command also puts the
whole chip into sleep mode, consuming very low
quiescent current to further improve the light load
efficiency.
PWM Control
At moderate to high output current, the MP2451
operates in a fixed frequency, peak current
control mode to regulate the output voltage. A
PWM cycle is initiated by the internal clock. The
power MOSFET is turned on and remains on
until its current reaches the value set by COMP
voltage. When the power switch is off, it remains
off for at least 100ns before the next cycle starts.
MP2451 Rev. 1.32
3/20/2014
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6
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© 2014 MPS. All Rights Reserved.
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
When COMP voltage is higher than the sleep
doesn't have another logic input acting as enable
signal. The resistor needs to be designed to limit
the EN pin sink current less than 100μA.
threshold, the PAUSE signal is reset so the chip
is back into normal PWM operation. Every time
when the PAUSE changes states from low to
high, a turn-on signal is generated right away,
turning on the power MOSFET.
Under Voltage Lockout (UVLO)
VIN Under voltage lockout (UVLO) is implemented
to protect the chip from operating at insufficient
supply voltage. The UVLO rising threshold is
about 2.9V while its trailing threshold is about
400mV lower.
Error Amplifier
The Error amplifier is composed of an internal
OP-AMP with an R-C feedback network
connected between its output node (internal
COMP node) and its negative input node (FB).
When FB is lower than its internal reference
voltage (REF), the COMP output is then driven
higher by the OP-AMP, causing higher switch
peak current output hence more energy delivered
to the output. Vise versus.
Internal Soft-start
Reference type 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 at a slow pace set by
the soft-start time. When it is lower than the
internal reference REF, SS overrides the REF so
the error amplifier uses SS instead of REF as the
reference. When SS is higher than REF, REF
gains the control back.
When connecting to the FB pin, normally there is
a voltage divider composed of RUP and RDN
where RDN is between FB and GND while RUP is
between the voltage output node and FB. RUP
serves also to control the gain of the error
amplifier along with the internal compensation R-
C network.
SS is also associated with FB. Though SS can
be much lower than FB, it can only be slightly
higher than FB. If somehow FB is brought down,
SS follows to track FB. This function is designed
to accommodate the short-circuit recovery
situation. When a short-circuit is removed, the SS
ramps up as if it is a fresh soft-start process. This
prevents output voltage overshoot.
Internal Regulator
Most of the internal circuitry is powered on by the
2.6V internal regulator. This regulator takes VIN
input and operates in the full VIN range. When
VIN is greater than 3.0V, the output of the
regulator is in full regulation. When VIN is lower,
the output degrades.
Thermal Shutdown
Thermal shutdown is implemented to prevent the
chip from thermally running away. When the
silicon die temperature is higher than its upper
threshold, it shuts down the whole chip. When
the temperature is lower than its lower threshold,
thermal shutdown is gone so the chip is enabled
again.
Enable Control
The MP2451 has a dedicated enable control pin
EN. With high enough VIN, the chip can be
enabled and disabled by EN pin. This is a HIGH
effective logic. Its rising threshold is 1.55V
typically and its trailing threshold is about 300mV
lower. When floating, EN pin is internally pulled
down to GND so the chip is disabled.
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 about 2.4V with a threshold of
about 300mV. During this UVLO, the SS voltage
of the controller is reset to zero. When the UVLO
is removed, the controller follows soft-start
process.
When EN is pulled down to 0V, the chip is put
into the lowest shutdown current mode. When
EN is higher than zero but lower than its rising
threshold, the chip is still in shutdown mode but
the shutdown current increases slightly.
Internally a zener diode is connected from EN pin
to GND pin. The typical clamping voltage of the
zener diode is 7.5V. So VIN can be connected to
EN through a high ohm resistor if the system
MP2451 Rev. 1.32
3/20/2014
www.MonolithicPower.com
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© 2014 MPS. All Rights Reserved.
7
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
The bootstrap capacitor is charged and regulated
to about 5V by the dedicated internal bootstrap
regulator. When the voltage between BST and
maximum current of the internal power MOSFET
is internally limited cycle by cycle.
Startup and Shutdown
SW nodes is lower than its regulation, a PMOS
pass transistor connected from VIN to BST is
turned on. The charging current path is from VIN,
BST and then to SW. External circuit should
provide enough voltage headroom to facilitate the
charging.
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 rest circuitries.
As long as VIN is sufficiently higher than SW, the
bootstrap capacitor can be charged. When the
power MOSFET is ON, VIN is about equal to SW
so the bootstrap capacitor cannot be charged.
When the external free wheeling diode is on, VIN
to SW difference is the largest so it is the best
period to charge. When there is no current in the
inductor, SW equals to the output voltage VOUT so
the difference between VIN and VOUT can be used
to charge the bootstrap capacitor.
While the internal supply rail is up, an internal
timer holds the power MOSFET OFF for about
50usec to blank the startup glitches. When the
internal soft-start block is enabled, it first holds its
SS output low to ensure the rest circuitries are
ready and then slowly ramps up.
Three events shut down the chip: EN low, VIN low,
thermal shutdown. In the shutdown procedure,
the signaling path is blocked first to avoid any
fault triggering. COMP voltage and the internal
supply rail are pulled down then. The floating
driver is not subject to this shutdown command
but its charging path is disabled.
At higher duty cycle operation condition, the time
period available to the bootstrap charging is less
so the bootstrap capacitor may not be charged
sufficiently.
In case the external circuit has not sufficient
voltage and time to charge the bootstrap
capacitor, extra external circuitry can be used to
ensure the bootstrap voltage in normal operation
region.
The floating driver’s UVLO is not communicated
to the controller.
The DC quiescent current of the floating driver is
about 20μA. Make sure the bleeding current at
SW node is at least higher than this number.
Current Comparator and Current Limit
The power MOSFET current is accurately sensed
via a current sense MOSFET. It is then fed to the
high speed current comparator for the current
mode control purpose. The current comparator
takes this sensed current as one of its inputs.
When the power MOSFET is turned on, the
comparator is first blanked till the end of the turn-
on transition to dodge the noise. Then, the
comparator compares the power switch current
with COMP voltage. When the sensed current is
higher than COMP voltage, the comparator
outputs low, turning off the power MOSFET. The
MP2451 Rev. 1.32
3/20/2014
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8
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
APPLICATION INFORMATION
COMPONENT SELECTION
Inductor
The inductor is required to supply constant
current to the output load while being driven by
Setting the Output Voltage
The output voltage is set using a resistive
voltage divider from the output voltage to FB pin.
The voltage divider divides the output voltage
down to the feedback voltage by the ratio:
the switched input voltage. A larger value
inductor will result in less ripple current that will
result in lower output ripple voltage. However,
the larger value inductor will have a larger
physical size, higher series resistance, and/or
lower saturation current.
R2
VFB = V
OUT R1+ R2
Thus the output voltage is:
Generally, a good rule for determining the
inductance to use is to allow the peak-to-peak
ripple current in the inductor to be
approximately 30% of the maximum load
current. Also, make sure that the peak inductor
current is below the maximum switch current
limit. The inductance value can be calculated by:
(R1+ R2)
VOUT = VFB
R2
The feedback resistor R1 also sets the
feedback loop bandwidth with the internal
compensation capacitor.
Choose R1 around 124kΩ for optimal transient
response. R2 is then given by:
⎛
⎜
⎝
⎞
⎟
⎟
⎠
VOUT
VOUT
⎜
L1=
× 1−
fS × ΔIL
V
IN
R1
R2 =
Where VOUT is the output voltage, VIN is the input
voltage, fS is the switching frequency, and ΔIL is
the peak-to-peak inductor ripple current.
VOUT
−1
0.8V
Table 1―Resistor Selection vs. Output
Choose an inductor that will not saturate under
the maximum inductor peak current. The peak
inductor current can be calculated by:
Voltage Setting
VOUT
0.8V
1.2V
3.3V
5V
R1
R2
NS
124kΩ (1%)
124kΩ (1%)
124kΩ (1%)
124kΩ (1%)
⎛
⎞
⎟
⎟
⎠
VOUT
VOUT
249kΩ (1%)
40.2kΩ (1%)
23.7kΩ (1%)
⎜
ILP = ILOAD
+
× 1−
⎜
⎝
2 × fS × L1
V
IN
Where ILOAD is the load current.
Table 2 lists a number of suitable inductors
from various manufacturers. The choice of
which style inductor to use mainly depends on
the price vs. size requirements and any EMI
requirement.
MP2451 Rev. 1.32
3/20/2014
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9
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
Table 2—Inductor Selection Guide
Inductance (µH) Max DCR (Ω) Current Rating (A)
Dimensions
Part Number
L x W x H (mm3)
Wurth Electronics
7440430022
2.2
3.3
4.7
0.028
0.035
0.078
2.5
2.15
2.4
4.8x4.8x2.8
4.8x4.8x2.8
5.9x6.2x3.2
744043003
7447785004
TOKO
D63CB-#A916CY-2R0M
D62CB-#A916CY-3R3M
D62CB-#A916CY-4R7M
TDK
2.0
3.3
4.7
0.019
0.026
0.032
2.36
2.17
2.1
6.2x6.3x3.0
6.2x6.3x3.0
6.2x6.3x3.0
2.2
3.3
4.7
0.04
0.06
3.2
2.5
2.0
5.2x5.0x2.2
5.2x5.0x2.2
5.2x5.0x2.2
LTF5022T-2R2N3R2
LTF5022T-3R3N2R5
LTF5022T-4R7N2R0
COOPER BUSSMANN
SD25-2R2
0.081
2.2
3.3
4.7
0.031
0.038
0.047
2.8
5.2x5.2x2.5
5.2x5.2x2.5
5.2x5.2x2.5
2.21
1.83
SD25-3R3
SD25-4R7
⎛
⎞
⎟
⎟
⎛
⎜
⎝
⎞
⎟
⎟
⎠
VOUT
VOUT
VIN
1
The input capacitor (C1) can be electrolytic,
tantalum or ceramic. When using electrolytic or
tantalum capacitors, 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:
⎜
⎜
ΔVOUT
=
× 1−
× RESR
+
⎜
fS × L
8 × fS × C2
⎝
⎠
Where L is the inductor value and RESR is the
equivalent series resistance (ESR) value of the
output capacitor.
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:
⎛
⎜
⎝
⎞
⎟
⎟
⎠
ILOAD
VOUT
VIN
VOUT
⎜
ΔV
=
×
× 1−
IN
⎛
⎞
⎟
⎟
⎠
fS × C1
V
VOUT
VOUT
IN
⎜
ΔVOUT
=
× 1−
8 × fS2 × L × C2
⎜
⎝
V
IN
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:
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.
MP2451 Rev. 1.32
3/20/2014
www.MonolithicPower.com
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© 2014 MPS. All Rights Reserved.
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
Compensation Components
External Bootstrap Diode
The goal of compensation design is to shape the
converter transfer function to get a desired loop
gain. Lower crossover frequencies result in
slower line and load transient responses, while
higher crossover frequencies could cause system
unstable. A good rule of thumb is to set the
crossover frequency to approximately one-tenth
of the switching frequency. If an electrolytic
capacitor is used, the loop bandwidth is no higher
than 1/4 of the ESR zero frequency (fESR). fESR is
given by:
An external bootstrap diode may enhance the
efficiency of the regulator. In below cases, an
external BST diode is recommended from the 5V
to BST pin:
z
z
z
There is a 5V rail available in the system;
VIN is no greater than 5V;
VOUT is between 3.3V and 5V;
This diode is also recommended for high duty
cycle operation (when VOUT / VIN > 65%)
applications.
1
fESR
=
2π × C2× RESR
The bootstrap diode can be a low cost one such
as IN4148 or BAT54.
The Table
3
lists the typical values of
compensation components for some standard
output voltages with various output capacitors
(ceramic) and inductors. The values of the
compensation components have been optimized
for fast transient responses and good stability at
given conditions.
5V
BS
MP2451
0.1uF
SW
Table 3—Compensation Values for Typical
Output Voltage/Capacitor Combinations
Figure 2—External Bootstrap Diode
VOUT(V) L(µH) C2(µF) R2(kꢀ) C3(pF)
At no load or light load, the converter may
operate in pulse skipping mode in order to
maintain the output voltage in regulation. Thus
there is less time to refresh the BS voltage. In
order to have enough gate voltage under such
operating conditions, the difference of VIN –VOUT
should be greater than 3V. For example, if the
VOUT is set to 3.3V, the VIN needs to be higher
than 3.3V+3V=6.3V to maintain enough BS
voltage at no load or light load. To meet this
requirement, EN pin can be used to program the
input UVLO voltage to VOUT+3V.
1.2
2.5
3.3
5
2.2
2.2
2.2
3.3
6.2
10
10
10
10
10
249
57.6
40.2
23.7
8.87
22
22
33
33
47
12
Note:
With the compensation, the control loop has the bandwidth at about
1/10 switching frequency and the phase margin higher than 45
degree.
MP2451 Rev. 1.32
3/20/2014
www.MonolithicPower.com
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11
© 2014 MPS. All Rights Reserved.
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
TYPICAL APPLICATION CIRCUITS
C4
100nF
VOUT
3.3V
6
1
SW
BST
D1
MP2451
VIN
6-24V
2
5
4
GND
VIN
EN
C1
3
FB
Control
C3
33pF
Figure 3—3.3V Output Typical Application Schematic
C4
100nF
VOUT
12V
6
1
2
SW
BST
D1
MP2451
VIN
18-36V
5
4
GND
VIN
EN
C1
3
FB
Control
C3
47pF
Figure 4—12V Output Typical Application Schematic
MP2451 Rev. 1.32
3/20/2014
www.MonolithicPower.com
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© 2014 MPS. All Rights Reserved.
12
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
PCB LAYOUT GUIDE
3) Ensure all feedback connections are short
and direct. Place the feedback resistors and
compensation components as close to the
chip as possible.
PCB layout is very important to achieve stable
operation. It is highly recommended to duplicate
EVB layout for optimum performance.
If change is necessary, please follow these
guidelines and take Figure 5 for reference.
4) Route SW away from sensitive analog areas
such as FB.
1) Keep the path of switching current short and
minimize the loop area formed by Input cap,
high-side MOSFET and external switching
diode.
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.
2) Bypass ceramic capacitors are suggested to
be put close to the VIN Pin.
BST
VIN
VIN
EN
C4
C1
R3
R4
MP2451
L1
VOUT
SW
FB
EN
C2
D1
R2
GND
R1
C3
MP2451 Typical Application Circuit
R1
C4
L1
C1
D1
C2
GND
GND
Vo
Vin
GND
TOP Layer
Bottom Layer
Figure 5―MP2451 Typical Application Circuit and PCB Layout Guide
MP2451 Rev. 1.32
3/20/2014
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2014 MPS. All Rights Reserved.
13
MP2451―36V, 2MHz, 0.6A, STEP-DOWN CONVERTER
PACKAGE INFORMATION
SOT23-6L
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.
MP2451 Rev. 1.32
3/20/2014
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2014 MPS. All Rights Reserved.
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