MP2351DQ-LF [MPS]
Switching Regulator, Current-mode, 5.2A, 1650kHz Switching Freq-Max, 3 X 3 MM, LEAD FREE, QFN-10;
| 型号： | MP2351DQ-LF |
| 厂家： | 
MONOLITHIC POWER SYSTEMS |
| 描述： | Switching Regulator, Current-mode, 5.2A, 1650kHz Switching Freq-Max, 3 X 3 MM, LEAD FREE, QFN-10 开关 |
| 文件： | 总8页 (文件大小：190K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MP2351
1.5A, 23V, 1.4MHz
Step-Down Converter
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP2351 is a monolithic step down switch
mode converter with a built in internal power
MOSFET. It achieves 1.5A continuous output
current over a wide input supply range with
excellent load and line regulation.
•
•
•
1.5A Output Current
0.18Ω Internal Power MOSFET Switch
Stable with Low ESR Output Ceramic
Capacitors
Up to 93% Efficiency
20μA Shutdown Mode
•
•
•
•
•
•
•
•
•
•
Current mode operation provides fast transient
response and eases loop stabilization.
Fixed 1.4MHz Frequency
Thermal Shutdown
Fault condition protection includes cycle-by-cycle
current limiting, short circuit frequency foldback
and thermal shutdown. In shutdown mode the
regulator draws 20μA of supply current.
Cycle-by-Cycle Over Current Protection
Wide 4.75V to 23V Operating Input Range
Output Adjustable from 1.23V to 16V
Programmable Under Voltage Lockout
Frequency Synchronization Input
Available in QFN (3mm x 3mm) and tiny
10-Pin MSOP Packages
The MP2351 requires a minimum number of
readily available standard external components.
EVALUATION BOARD REFERENCE
•
Evaluation Board Available
Board Number
Dimensions
APPLICATIONS
EV2351DQ-00A
2.3”X x 1.5”Y x 0.5”Z
•
•
•
•
Distributed Power Systems
Battery Charger
DSL Modems
Pre-Regulator for Linear Regulators
“MPS” and “The Future of Analog IC Technology” are Registered Trademarks of
Monolithic Power Systems, Inc.
TYPICAL APPLICATION
INPUT
4.75V - 23V
Efficiency vs
Load Current
C5
10nF
100
4
V
=5V
2
OUT
90
80
70
60
50
40
IN
BS
OPEN
9
5
V
OUT
3.3V/1.5A
AUTOMATIC
STARTUP
EN
SW
FB
D1
B220A
V
=2.5V
OUT
MP2351
10
7
SYNC
GND
6
OPEN
NOT USED
V
=3.3V
OUT
COMP
8
C3
1nF
C6
OPEN
0
300 600 900 1200 1500
LOAD CURRENT (mA)
MP2351_TAC_S01
MP2351-EC01
MP2351 Rev. 1.6
9/21/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
1
MP2351 – 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER
PACKAGE REFERENCE
TOP VIEW
TOP VIEW
NC
BS
NC
IN
1
2
3
4
5
10 SYNC
9
8
7
6
EN
NC
BS
NC
IN
1
2
3
4
5
10
9
SYNC
EN
COMP
FB
8
COMP
FB
7
SW
GND
SW
6
GND
EXPOSED PAD
ON BACKSIDE
CONNECT TO
MP2351_PD01-QFN10
MP2351_PD01-MSOP10
GROUND (PIN 6)
Part Number*
MP2351DQ
Package
Temperature
–40°C to +85°C
Part Number*
Package
Temperature
–40°C to +85°C
QFN10
(3mm x 3mm)
MP2351DK
MSOP10
For Tape & Reel, add suffix –Z (eg. MP2351DQ–Z)
For Lead Free, add suffix –LF (eg. MP2351DQ –LF–Z)
*
For Tape & Reel, add suffix –Z (eg. MP2351DK–Z)
For Lead Free, add suffix –LF (eg. MP2351DK –LF–Z)
*
ABSOLUTE MAXIMUM RATINGS (1)
Supply Voltage (VIN)..................................... 25V
Switch Voltage (VSW).................................... 26V
Bootstrap Voltage (VBS) .......................VSW + 6V
Feedback Voltage (VFB) .................–0.3V to +6V
Enable/UVLO Voltage (VEN)...........–0.3V to +6V
Comp Voltage (VCOMP) ...................–0.3V to +6V
Sync Voltage (VSYNC)......................–0.3V to +6V
Junction Temperature.............................+150°C
Lead Temperature ..................................+260°C
Storage Temperature.............. –65°C to +150°C
Recommended Operating Conditions (2)
Supply Voltage (VIN) ...................... 4.75V to 23V
Operating Temperature.................–40°C to +85°C
Thermal Resistance (3)
θJA
θJC
QFN10 (3x3)...........................50...... 12... °C/W
MSOP10................................150..... 65... °C/W
Notes:
1) Exceeding these ratings may damage the device.
2) The device is not guaranteed to function outside of its
operating conditions.
3) Measured on approximately 1” square of 1 oz copper.
ELECTRICAL CHARACTERISTICS
VIN = 12V, TA = +25°C, unless otherwise noted.
Parameter
Symbol Condition
Min
Typ
1.230
0.18
10
0
2.8
Max
Units
V
Feedback Voltage
VFB
1.195
1.265
4.75V ≤ VIN ≤ 23V
Upper Switch-On Resistance
Lower Switch-On Resistance
Upper Switch Leakage
Current Limit (4)
RDS(ON)1
RDS(ON)2
Ω
Ω
μA
A
VEN = 0V, VSW = 0V
10
5.2
2.4
Current Sense Transconductance
Output Current to Comp Pin Voltage
GCS
1.95
A/V
Error Amplifier Voltage Gain
Error Amplifier Transconductance
Oscillator Frequency
Short Circuit Frequency
Sync Frequency
AVEA
GEA
fS
400
770
1.40
180
V/V
μA/V
MHz
KHz
MHz
500
1100
1.65
ΔIC = ±10 μA
1.15
VFB = 0V
Sync Drive 0V to 2.7V
1.6
2.1
MP2351 Rev. 1.6
9/21/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
2
MP2351 – 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER
ELECTRICAL CHARACTERISTICS (continued)
VIN = 12V, TA = +25°C, unless otherwise noted.
Parameter
Symbol Condition
Min
Typ
70
Max
Units
%
Maximum Duty Cycle
Minimum On Time
DMAX VFB = 1.0V
TON (MIN) VFB = 1.5V
ICC > 100μA
70
ns
EN Shutdown Threshold Voltage
Enable Pull Up Current
EN UVLO Threshold Rising
EN UVLO Threshold Hysteresis
Supply Current (Shutdown)
Supply Current (Quiescent)
Thermal Shutdown
0.7
1.0
1.50
2.50
210
20
1.3
V
VEN = 0V
1.15
2.37
μA
V
VEN Rising
2.62
mV
μA
mA
°C
36
VEN ≤ 0.4V
1.1
160
1.3
VEN ≥ 3V, VFB = 1.4V
Note:
4) Equivalent output current = 1.5A ≥ 50% Duty Cycle
2.0A ≤ 50% Duty Cycle
Assumes ripple current = 30% of load current.
Slope compensation changes current limit above 40% duty cycle.
PIN FUNCTIONS
Pin # Name Description
1
2
NC
BS
No Connect.
Bootstrap (C5). This capacitor is needed to drive the power switch’s gate above the supply
voltage. It is connected between SW and BS pins to form a floating supply across the power
switch driver. The voltage across C5 is about 5V and is supplied by the internal +5V supply
when the SW pin voltage is low.
3
4
NC
IN
No Connect.
Supply Voltage. The MP2351 operates from a +4.75V to +23V unregulated input. C1 is needed
to prevent large voltage spikes from appearing at the input.
5
6
SW Switch. This connects the inductor to either IN through M1 or to GND through M2.
GND Ground. This pin is the voltage reference for the regulated output voltage. For this reason care
must be taken in its layout. This node should be placed outside of the D1 to C1 ground path to
prevent switching current spikes from inducing voltage noise into the part.
7
FB
Feedback. An external resistor divider from the output to GND, tapped to the FB pin sets the
output voltage. To prevent current limit run away during a short circuit fault condition the
frequency foldback comparator lowers the oscillator frequency when the FB voltage is below
700mV.
8
9
COMP Compensation. This node is the output of the transconductance error amplifier and the input to the
current comparator. Frequency compensation is done at this node by connecting a series R-C to
ground. See the compensation section for exact details.
EN
Enable/UVLO. A voltage greater than 2.62V enables operation. Leave EN unconnected for
automatic startup. An Under Voltage Lockout (UVLO) function can be implemented by the
addition of a resistor divider from VIN to GND. For complete low current shutdown it’s the EN
pin voltage needs to be less than 700mV.
10
SYNC Synchronization Input. This pin is used to synchronize the internal oscillator frequency to an
external source. There is an internal 11kΩ pull down resistor to GND, therefore leave SYNC
unconnected if unused.
MP2351 Rev. 1.6
9/21/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
3
MP2351 – 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER
OPERATION
The MP2351 is a current mode regulator. That
is, the COMP pin voltage is proportional to the
peak inductor current. At the beginning of a
cycle: the upper transistor M1 is off; the lower
transistor M2 is on; the COMP pin voltage is
higher than the current sense amplifier output;
and the current comparator’s output is low. The
rising edge of the 1.4MHz CLK signal sets the
RS Flip-Flop. Its output turns off M2 and turns
on M1 thus connecting the SW pin and inductor
to the input supply. The increasing inductor
current is sensed and amplified by the Current
Sense Amplifier. Ramp compensation is
summed to Current Sense Amplifier output and
compared to the Error Amplifier output by the
Current Comparator. When the Current Sense
Amplifier plus Slope Compensation signal
exceeds the COMP pin voltage, the RS
Flip-Flop is reset and the MP2351 reverts to its
initial M1 off, M2 on state. If the Current Sense
Amplifier plus Slope Compensation signal does
not exceed the COMP voltage, then the falling
edge of the CLK resets the Flip-Flop.
The output of the Error Amplifier integrates the
voltage difference between the feedback and
the 1.230V bandgap reference. The polarity is
such that an FB pin voltage lower than 1.230V
increases the COMP pin voltage. Since the
COMP pin voltage is proportional to the peak
inductor current an increase in its voltage
increases current delivered to the output. The
lower 10Ω switch ensures that the bootstrap
capacitor voltage is charged during light load
conditions. External Schottky Diode D1 carries
the inductor current when M1 is off.
4
IN
CURRENT
SENSE
INTERNAL
REGULATORS
AMPLIFIER
+
--
5V
OSCILLATOR
10
SYNC
SLOPE
COMP
180KHz/
1.4MHz
2
5
BS
CLK
+
--
+
S
R
Q
Q
SW
CURRENT
COMPARATOR
SHUTDOWN
COMPARATOR
--
0.7V
9
EN
LOCKOUT
COMPARATOR
--
+
1.8V
2.37V/
2.62V
+
--
6
GND
0.7V 1.23V
7
--
+
FREQUENCY
FOLDBACK
COMPARATOR
ERROR
AMPLIFIER
8
FB
COMP
MP2351_BD01
Figure 1—Functional Block Diagram
MP2351 Rev. 1.6
9/21/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
4
MP2351 – 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER
APPLICATION INFORMATION
COMPONENT SELECTION
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:
Choose an inductor that will not saturate under
the maximum inductor peak current. The peak
inductor current can be calculated by:
⎛
⎞
VOUT
VOUT
VIN
⎜
⎟
⎟
⎠
ILP = ILOAD
+
× 1−
⎜
⎝
2× fS ×L
Where, ILOAD is the load current.
R2
VFB = VOUT
R1+ R2
Output Rectifier Diode
The output rectifier diode supplies the current to
the inductor when the high-side switch is off. To
reduce losses due to the diode forward voltage
and recovery times, use a Schottky diode.
Where VFB is the feedback voltage and VOUT is
the output voltage.
Thus the output voltage is:
R1+ R2
Choose a diode whose maximum reverse
voltage rating is greater than the maximum
input voltage, and whose current rating is
greater than the maximum load current.
VOUT = 1.23 ×
R2
R2 can be as high as 100kΩ, but a typical value
is 10kΩ. Using that value, R1 is determined by:
Input Capacitor
R1 = 8.18 × (VOUT − 1.23)
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 are preferred,
but tantalum or low-ESR electrolytic capacitors
may also suffice.
For example, for a 3.3V output voltage, R2 is
10kΩ, and R1 is 17kΩ.
Inductor
The inductor is required to supply constant
current to the output load while being driven by
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. 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
switch current limit. Also, make sure that the
peak inductor current is below the maximum
switch current limit. The inductance value can
be calculated by:
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:
⎛
⎞
⎟
VOUT
VIN
VOUT
VIN
⎜
IC1 = ILOAD
×
× 1−
⎜
⎝
⎟
⎠
The worst-case condition occurs at VIN = 2VOUT
,
where:
ILOAD
IC1
=
2
⎛
⎞
⎟
⎟
⎠
VOUT
VOUT
⎜
L =
× 1−
For simplification, choose the input capacitor
whose RMS current rating greater than half of
the maximum load current.
⎜
⎝
fS × ΔIL
V
IN
Where VIN is the input voltage, fS is the
switching frequency and ΔIL is the peak-to-peak
inductor ripple current.
MP2351 Rev. 1.6
9/21/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
5
MP2351 – 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER
The input capacitor can be electrolytic, tantalum
Compensation Components
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:
The MP2351 employs current mode control for
easy compensation and fast transient response.
The system stability and transient response are
controlled through the COMP pin. COMP pin is
the output of the internal transconductance
error amplifier. A series capacitor-resistor
combination sets a pole-zero combination to
control the characteristics of the control system.
The DC gain of the voltage feedback loop is:
VFB
⎛
⎞
⎟
⎟
⎠
ILOAD
VOUT
VIN
VOUT
⎜
ΔV
=
×
× 1−
IN
⎜
⎝
AVDC = RLOAD × GCS × AVEA
×
fS × C1
V
IN
VOUT
Output Capacitor
Where AVEA is the error amplifier voltage gain,
GCS is the current sense transconductance and
The output capacitor 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:
RLOAD is the load resistor value.
The system has two poles of importance. One
is due to the compensation capacitor (C3) and
the output resistor of error amplifier, and the
other is due to the output capacitor and the load
resistor. These poles are located at:
⎛
⎜
⎝
⎞
⎟
⎟
⎛
⎜
⎝
⎞
⎟
⎟
⎠
VOUT
VOUT
VIN
1
⎜
⎜
ΔVOUT
=
× 1−
× RESR
+
fS × L
8 × fS × C2
⎠
GEA
fP1
=
2π× C3× AVEA
Where RESR is the equivalent series resistance
(ESR) value of the output capacitor and C2 is
the output capacitance value.
1
fP2
=
2π × C2× RLOAD
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:
Where
transconductance.
GEA
is
the
error
amplifier
The system has one zero of importance, due to
the compensation capacitor (C3) and the
compensation resistor (R3). This zero is located
at:
⎛
⎜
⎝
⎞
VOUT
VOUT
VIN
⎜
⎟
⎟
⎠
ΔVOUT
=
× 1−
2
8 × fS × L × C2
1
fZ1
=
2π × C3×R3
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:
The system may have another zero of
importance, if the output capacitor has a large
capacitance and/or a high ESR value. The zero,
due to the ESR and capacitance of the output
capacitor, is located at:
VOUT
VOUT
⎛
⎞
ΔVOUT
=
× ⎜1−
⎟ ×RESR
⎜
⎟
fS ×L
VIN
⎝
⎠
1
fESR
=
The characteristics of the output capacitor also
affect the stability of the regulation system. The
MP2351 can be optimized for a wide range of
capacitance and ESR values.
2π × C2× RESR
MP2351 Rev. 1.6
9/21/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
6
MP2351 – 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER
In this case, a third pole set by the
3. Determine if the second compensation
capacitor (C6) is required. It is required if the
ESR zero of the output capacitor is located at
less than half of the switching frequency, or the
following relationship is valid:
compensation capacitor (C6) and the
compensation resistor (R3) is used to
compensate the effect of the ESR zero on the
loop gain. This pole is located at:
fS
2
1
1
fP3
=
<
2π × C6 × R3
2π × C2× RESR
The goal of compensation design is to shape
the converter transfer function to get a desired
loop gain. The system crossover frequency
where the feedback loop has the unity gain is
important.
If this is the case, then add the second
compensation capacitor (C6) to set the pole fP3
at the location of the ESR zero. Determine the
C6 value by the equation:
C2 × RESR
C6 =
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 below one-tenth of the
switching frequency.
R3
External Bootstrap Diode
It is recommended that an external bootstrap
diode be added when the system has a 5V
fixed input or the power supply generates a 5V
output. This helps improve the efficiency of the
regulator. The bootstrap diode can be a low
cost one such as IN4148 or BAT54.
To optimize the compensation components, the
following procedure can be used:
1. Choose the compensation resistor (R3) to set
the desired crossover frequency. Determine the
R3 value by the following equation:
5V
BS
2π × C2× fC VOUT
R3 =
×
10nF
MP2351
GEA × GCS
VFB
SW
Where fC is the desired crossover frequency,
which is typically less than one tenth of the
switching frequency.
MP2351_F02
Figure 2—External Bootstrap Diode
2. Choose the compensation capacitor (C3) to
achieve the desired phase margin. For
applications with typical inductor values, setting
the compensation zero, fZ1, to below one forth
of the crossover frequency provides sufficient
phase margin. Determine the C3 value by the
following equation:
This diode is also recommended for high duty
VOUT
cycle operation (when
>65%) and high
VIN
output voltage (VOUT>12V) applications.
4
C3 >
2π × R3 × fC
Where R3 is the compensation resistor.
MP2351 Rev. 1.6
9/21/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
7
MP2351 – 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER
PACKAGE INFORMATION
QFN10 (3mm x 3mm)
0.35
0.45
Pin1
Identification
R0.200TYP
2.95
3.05
Pin1
Identification
0.20
0.30
10
1
2.35
2.000
QFN10L
(3x3mm)
2.95
3.05
2.45
Ref
Exp.DAP
0.500
Bsc
6
5
1.65
1.75
Exp.DAP
TopView
BottomView
0.85
0.95
0.178
0.228
0.000-
0.050
SideView
Note:
1)Dimensionsareinmillimeters.
MSOP10
0.0197(0.500)TYP
10
6
0.004(0.100)
0.008(0.200)
PIN1
IDENT.
0.114(2.900)
0.122(3.100)
0.184(4.700)
0.200(5.100)
SEE DETAIL "A"
0.014(0.350)TYP
0.014(0.350)TYP
GATE PLANE 0.010(0.250)
1
5
0o-6o
DETAIL "A"
0.017(0.400)
0.025(0.600)
0.030(0.750)
0.038(0.950)
0.032(0.800)
0.044(1.100)
0.002(0.050)
0.006(0.150)
0.008(0.200)REF
NOTE:
1) Control dimension is in inches. Dimension in bracket is millimeters.
2) Package length does not include mold flash, protrusions or gate burr.
3) Package width does not include interlead flash or protrusions.
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.
MP2351 Rev. 1.6
9/21/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
8
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