MPS MP29296 2a, 23v synchronous rectified step-down converter Datasheet

MP29296
2A, 23V Synchronous Rectified
Step-Down Converter
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP29296 is a monolithic synchronous buck
regulator. The device integrates 130mΩ
MOSFETS that provide 2A continuous load
current over a wide operating input voltage of
4.75V to 23V. Current mode control provides
fast transient response and cycle-by-cycle
current limit.
•
•
•
•
•
•
•
•
•
•
An adjustable soft-start prevents inrush current
at turn-on. Shutdown mode drops the supply
current to 1µA.
This device, available in an 8-pin SOIC
package, provides a very compact system
solution with minimal reliance on external
components.
EVALUATION BOARD REFERENCE
Board Number
Dimensions
EV29296DS-00A
2.0”X x 1.5”Y x 0.5”Z
2A Output Current
Wide 4.75V to 23V Operating Input Range
Integrated 130mΩ Power MOSFET Switches
Output Adjustable from 0.923V to 20V
Up to 93% Efficiency
Programmable Soft-Start
Stable with Low ESR Ceramic Output Capacitors
Fixed 340KHz Frequency
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
APPLICATIONS
•
•
•
•
•
Distributed Power Systems
Networking Systems
FPGA, DSP, ASIC Power Supplies
Green Electronics/ Appliances
Notebook Computers
“MPS” and “The Future of Analog IC Technology” are Registered Trademarks of
Monolithic Power Systems, Inc.
TYPICAL APPLICATION
C5
10nF
INPUT
4.75V to 23V
Efficiency vs
Load Current
100
VOUT = 3.3V
95
7
90
1
IN
BS
3
SW
EN
MP29296
8
SS
GND
4
FB
COMP
5
6
C3
3.3nF
OUTPUT
3.3V
2A
EFFICIENCY (%)
2
85
VOUT = 2.5V
80
75
70
65
60
55
50
MP29296 Rev. 1.7
2/5/2010
0
0.5
1.0
1.5
2.0
LOAD CURRENT (A)
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
2.5
1
MP29296 – 2A, 23V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER
ABSOLUTE MAXIMUM RATINGS (1)
PACKAGE REFERENCE
Supply Voltage VIN ....................... –0.3V to +26V
Switch Voltage VSW .................. –1V to VIN +0.3V
Boost Voltage VBS ..........VSW – 0.3V to VSW + 6V
All Other Pins................................. –0.3V to +6V
Junction Temperature...............................150°C
Lead Temperature ....................................260°C
Storage Temperature .............–65°C to +150°C
TOP VIEW
BS
1
8
SS
IN
2
7
EN
SW
3
6
COMP
GND
4
5
FB
Recommended Operating Conditions
(2)
Input Voltage VIN ............................ 4.75V to 23V
Output Voltage VOUT .................... 0.923V to 20V
Ambient Operating Temperature .... –40°C to +85°C
Thermal Resistance
(3)
θJA
θJC
SOIC8..................................... 90 ...... 45... °C/W
Part Number*
Package
Temperature
MP29296DS
SOIC8
–40° to +85°C
*
For Tape & Reel, add suffix –Z (eg. MP29296DS–Z)
For Lead Free, add suffix –LF (eg. MP29296DS–LF–Z)
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
Shutdown Supply Current
Supply Current
Feedback Voltage
Error Amplifier Transconductance
High-Side Switch On Resistance (4)
Low-Side Switch On Resistance (4)
High-Side Switch Leakage Current
Upper Switch Current Limit
Lower Switch Current Limit
COMP to Current Sense
Transconductance
Oscillation Frequency
Short Circuit Oscillation Frequency
Maximum Duty Cycle
Minimum On Time (4)
EN Shutdown Threshold Voltage
EN Shutdown Threshold Voltage
Hysteresis
EN Lockout Threshold Voltage
EN Lockout Hysterisis
MP29296 Rev. 1.7
2/5/2010
VEN = 0V
VEN = 2.0V; VFB = 1.0V
VFB
Feedback Overvoltage Threshold
Error Amplifier Voltage Gain (4)
Min
4.75V ≤ VIN ≤ 23V
0.900
AEA
GEA
∆IC = ±10µA
RDS(ON)1
RDS(ON)2
VEN = 0V, VSW = 0V
Minimum Duty Cycle
From Drain to Source
2.4
VFB = 0V
VFB = 1.0V
VEN Rising
Max
Units
1
1.3
3.0
1.5
µA
mA
0.923
0.946
V
1.1
400
V
V/V
800
µA/V
130
130
3.4
1.1
mΩ
mΩ
µA
A
A
3.5
A/V
340
100
90
220
1.5
KHz
KHz
%
ns
V
10
GCS
Fosc1
Fosc2
DMAX
Typ
1.1
2.0
210
2.2
2.5
210
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
mV
2.7
V
mV
2
MP29296 – 2A, 23V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER
ELECTRICAL CHARACTERISTICS (continued)
VIN = 12V, TA = +25°C, unless otherwise noted.
Parameter
Input Under Voltage Lockout
Threshold
Input Under Voltage Lockout
Threshold Hysteresis
Soft-Start Current
Soft-Start Period
Thermal Shutdown (4)
Symbol Condition
Min
Typ
Max
Units
VIN Rising
3.80
4.10
4.40
V
VSS = 0V
CSS = 0.1µF
210
mV
6
15
160
µA
ms
°C
Note:
4) Guaranteed by design, not tested.
PIN FUNCTIONS
Pin #
Name
1
BS
2
IN
3
SW
4
GND
5
FB
6
COMP
7
EN
8
SS
MP29296 Rev. 1.7
2/5/2010
Description
High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N-Channel MOSFET
switch. Connect a 0.01µF or greater capacitor from SW to BS to power the high side switch.
Power Input. IN supplies the power to the IC, as well as the step-down converter switches.
Drive IN with a 4.75V to 23V power source. Bypass IN to GND with a suitably large capacitor
to eliminate noise on the input to the IC. See Input Capacitor.
Power Switching Output. SW is the switching node that supplies power to the output. Connect
the output LC filter from SW to the output load. Note that a capacitor is required from SW to
BS to power the high-side switch.
Ground.
Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a
resistive voltage divider from the output voltage. The feedback threshold is 0.923V. See
Setting the Output Voltage.
Compensation Node. COMP is used to compensate the regulation control loop. Connect a
series RC network from COMP to GND to compensate the regulation control loop. In some
cases, an additional capacitor from COMP to GND is required. See Compensation
Components.
Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to turn on
the regulator, drive it low to turn it off. Pull up with 100kΩ resistor for automatic startup.
Soft-Start Control Input. SS controls the soft start period. Connect a capacitor from SS to GND
to set the soft-start period. A 0.1µF capacitor sets the soft-start period to 15ms. To disable the
soft-start feature, leave SS unconnected.
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
3
MP29296 – 2A, 23V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, VO = 3.3V, L = 10µH, C1 = 10µF, C2 = 22µF, TA = +25°C, unless otherwise noted.
VOUT
20mV/div.
IL
1A/div.
VEN
5V/div.
VEN
5V/div.
VOUT
2V/div.
VOUT
2V/div.
IL
1A/div.
IL
1A/div.
VSW
10V/div.
VSW
10V/div.
VIN = 12V, VOUT = 3.3V
IOUT = 1A (Resistance Load)
VIN = 12V, VOUT = 3.3V
IOUT = 1A (Resistance Load)
VIN = 12V, VOUT = 3.3V
IOUT = 0A, IIN= 8.2mA
VIN
20mV/div.
Shutdown through Enable
Startup through Enable
Steady State Test
VSW
10V/div.
2ms/div.
2ms/div.
Heavy Load Operation
Medium Load Operation
Light Load Operation
2A Load
1A Load
No Load
VIN, AC
200mV/div.
VIN, AC
200mV/div.
VIN, AC
20mV/div.
VO, AC
20mV/div.
VO, AC
20mV/div.
VO, AC
20mV/div.
IL
1A/div.
IL
1A/div.
VSW
10V/div.
VSW
10V/div.
IL
1A/div.
VSW
10V/div.
Short Circuit
Recovery
Short Circuit
Protection
VOUT
2V/div.
IL
2A/div.
MP29296 Rev. 1.7
2/5/2010
VOUT
2V/div.
Load Transient
VOUT
200mV/div.
IL
1A/div.
IL
2A/div.
ILOAD
1A/div.
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
4
MP29296 – 2A, 23V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER
OPERATION
FUNCTIONAL DESCRIPTION
The MP29296 is a synchronous rectified,
current-mode, step-down regulator. It regulates
input voltages from 4.75V to 23V down to an
output voltage as low as 0.923V, and supplies
up to 2A of load current.
The MP29296 uses current-mode control to
regulate the output voltage. The output voltage
is measured at FB through a resistive voltage
divider and amplified through the internal
transconductance error amplifier. The voltage at
the COMP pin is compared to the switch current
measured internally to control the output
voltage.
The converter uses internal N-Channel
MOSFET switches to step-down the input
voltage to the regulated output voltage. Since
the high side MOSFET requires a gate voltage
greater than the input voltage, a boost capacitor
connected between SW and BS is needed to
drive the high side gate. The boost capacitor is
charged from the internal 5V rail when SW is low.
When the MP29296 FB pin exceeds 20% of the
nominal regulation voltage of 0.923V, the over
voltage comparator is tripped and the COMP
pin and the SS pin are discharged to GND,
forcing the high-side switch off.
+
CURRENT
SENSE
AMPLIFIER
OVP
1.1V
-OSCILLATOR
+
FB 5
100/340KHz
0.3V
RAMP
+
+
+
ERROR
AMPLIFIER
S
Q
BS
R
Q
3
SW
4
GND
CURRENT
COMPARATOR
COMP 6
2.5V
1
5V
---
0.923V
IN
--
CLK
--
SS 8
+
2
1.2V
+
EN
EN OK
--
OVP
IN < 4.10V
LOCKOUT
COMPARATOR
IN
+
EN 7
INTERNAL
REGULATORS
1.5V
--
5V
SHUTDOWN
COMPARATOR
Figure 1—Functional Block Diagram
MP29296 Rev. 1.7
2/5/2010
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
5
MP29296 – 2A, 23V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER
APPLICATIONS 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:
VFB = VOUT
Where VFB is the feedback voltage and VOUT is
the output voltage.
Thus the output voltage is:
R1 + R2
R2
R2 can be as high as 100kΩ, but a typical value
is 10kΩ. Using the typical value for R2, R1 is
determined by:
R1 = 10.83 × ( VOUT − 0.923 ) (kΩ)
For example, for a 3.3V output voltage, R2 is
10kΩ, and R1 is 26.1kΩ.
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:
L=
⎛
VOUT
V
× ⎜⎜1 − OUT
f S × ∆I L ⎝
VIN
⎞
⎟⎟
⎠
Where VOUT is the output voltage, VIN is the
input voltage, fS is the switching frequency, and
∆IL is the peak-to-peak inductor ripple current.
MP29296 Rev. 1.7
2/5/2010
ILP = ILOAD +
⎛
VOUT
V
× ⎜⎜1 − OUT
2 × fS × L ⎝
VIN
⎞
⎟⎟
⎠
Where ILOAD is the load current.
R2
R1 + R2
VOUT = 0.923 ×
Choose an inductor that will not saturate under
the maximum inductor peak current. The peak
inductor current can be calculated by:
The choice of which style inductor to use mainly
depends on the price vs. size requirements and
any EMI requirements.
Optional Schottky Diode
During the transition between high-side switch
and low-side switch, the body diode of the lowside power MOSFET conducts the inductor
current. The forward voltage of this body diode
is high. An optional Schottky diode may be
paralleled between the SW pin and GND pin to
improve overall efficiency. Table 1 lists example
Schottky diodes and their Manufacturers.
Table 1—Diode Selection Guide
Part Number
Voltage/Current
Rating
B130
SK13
MBRS130
30V, 1A
30V, 1A
30V, 1A
Vendor
Diodes, Inc.
Diodes, Inc.
International
Rectifier
Input Capacitor
The input current to the step-down converter is
discontinuous, therefore a capacitor is required
to supply the AC current to the step-down
converter while maintaining the DC input
voltage. Use low ESR capacitors for the best
performance. Ceramic capacitors are preferred,
but tantalum or low-ESR electrolytic capacitors
may also suffice. Choose X5R or X7R
dielectrics when using ceramic capacitors.
Since the input capacitor (C1) absorbs the input
switching current it requires an adequate ripple
current rating. The RMS current in the input
capacitor can be estimated by:
I C1 = ILOAD ×
VOUT ⎛⎜ VOUT ⎞⎟
× 1−
VIN ⎜⎝
VIN ⎟⎠
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
6
MP29296 – 2A, 23V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER
The worst-case condition occurs at VIN = 2VOUT,
where IC1 = ILOAD/2. For simplification, choose
the input capacitor whose RMS current rating
greater than half of the maximum load current.
The characteristics of the output capacitor also
affect the stability of the regulation system. The
MP29296 can be optimized for a wide range of
capacitance and ESR values.
The input capacitor 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 for low ESR capacitors can
be estimated by:
Compensation Components
MP29296 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.
∆VIN =
⎛
ILOAD
V
V
× OUT × ⎜⎜1 − OUT
C1 × fS
VIN ⎝
VIN
⎞
⎟⎟
⎠
Where C1 is the input capacitance value.
Output Capacitor
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:
∆VOUT =
VOUT ⎛
V
× ⎜⎜1 − OUT
fS × L ⎝
VIN
⎞
⎞ ⎛
1
⎟
⎟⎟ × ⎜ R ESR +
⎜
8 × f S × C2 ⎟⎠
⎠ ⎝
Where C2 is the output capacitance 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:
∆VOUT =
⎛
V
× ⎜⎜1 − OUT
VIN
× L × C2 ⎝
VOUT
8 × fS
2
⎞
⎟⎟
⎠
In the case of tantalum or electrolytic capacitors,
the ESR dominates the impedance at the
switching frequency. For simplification, the
output ripple can be approximated to:
∆VOUT =
MP29296 Rev. 1.7
2/5/2010
VOUT ⎛
V
× ⎜1 − OUT
f S × L ⎜⎝
VIN
⎞
⎟⎟ × R ESR
⎠
The DC gain of the voltage feedback loop is
given by:
A VDC = R LOAD × G CS × A EA ×
VFB
VOUT
Where AVEA is the error amplifier voltage gain;
GCS is the current sense transconductance and
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 the error amplifier, and the
other is due to the output capacitor and the load
resistor. These poles are located at:
fP1 =
GEA
2π × C3 × A VEA
fP2 =
1
2π × C2 × R LOAD
Where GEA is the error amplifier transconductance.
The system has one zero of importance, due to the
compensation capacitor (C3) and the compensation
resistor (R3). This zero is located at:
f Z1 =
1
2π × C3 × R3
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:
fESR =
1
2π × C2 × R ESR
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
7
MP29296 – 2A, 23V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER
In this case (as shown in Figure 2), a third pole
set by the 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:
fP 3 =
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:
f
1
< S
2π × C2 × R ESR
2
1
2π × C6 × R3
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. Lower crossover frequencies result
in slower line and load transient responses,
while higher crossover frequencies could cause
system instability. A good rule of thumb is to set
the crossover frequency below one-tenth of the
switching frequency.
To optimize the compensation components, the
following procedure can be used.
1. Choose the compensation resistor (R3) to set
the desired crossover frequency.
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:
C6 =
C2 × R ESR
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.
5V
Determine the R3 value by the following
equation:
R3 =
BS
2π × C2 × fC VOUT 2π × C2 × 0.1 × fS VOUT
×
<
×
GEA × GCS
VFB
GEA × GCS
VFB
Where fC is the desired crossover frequency
which is typically below one tenth of the
switching frequency.
2. Choose the compensation capacitor (C3) to
achieve the desired phase margin. For
applications with typical inductor values, setting
the compensation zero, fZ1, below one-forth of
the crossover frequency provides sufficient
phase margin.
10nF
MP29296
SW
Figure 2—External Bootstrap Diode
This diode is also recommended for high duty
cycle operation (when
output
voltage
VOUT
>65%) and high
VIN
(VOUT>12V)
applications
Determine the C3 value by the following equation:
C3 >
4
2π × R3 × f C
Where R3 is the compensation resistor.
MP29296 Rev. 1.7
2/5/2010
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
8
MP29296 – 2A, 23V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER
TYPICAL APPLICATION CIRCUIT
C5
10nF
INPUT
4.75V to 23V
2
7
1
IN
OUTPUT
3.3V
2A
BS
3
SW
EN
MP29296
8
SS
GND
FB
COMP
4
5
6
C6
(optional)
C3
3.3nF
D1
B130
(optional)
Figure 3—MP29296 with 3.3V Output, 22µF/6.3V Ceramic Output Capacitor
MP29296 Rev. 1.7
2/5/2010
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
9
MP29296 – 2A, 23V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER
PACKAGE INFORMATION
SOIC8
0.189(4.80)
0.197(5.00)
0.050(1.27)
0.024(0.61)
8
5
0.063(1.60)
0.150(3.80)
0.157(4.00)
PIN 1 ID
1
0.228(5.80)
0.244(6.20)
0.213(5.40)
4
TOP VIEW
RECOMMENDED LAND PATTERN
0.053(1.35)
0.069(1.75)
SEATING PLANE
0.004(0.10)
0.010(0.25)
0.013(0.33)
0.020(0.51)
0.0075(0.19)
0.0098(0.25)
SEE DETAIL "A"
0.050(1.27)
BSC
SIDE VIEW
FRONT VIEW
0.010(0.25)
x 45o
0.020(0.50)
GAUGE PLANE
0.010(0.25) BSC
0o-8o
0.016(0.41)
0.050(1.27)
DETAIL "A"
NOTE:
1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN
BRACKET IS IN MILLIMETERS.
2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH,
PROTRUSIONS OR GATE BURRS.
3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH
OR PROTRUSIONS.
4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING)
SHALL BE 0.004" INCHES MAX.
5) DRAWING CONFORMS TO JEDEC MS-012, VARIATION AA.
6) DRAWING IS NOT TO SCALE.
NOTICE: The information in this document is subject to change without notice. Users should warrant and guarantee that third
party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not
assume any legal responsibility for any said applications.
MP29296 Rev. 1.7
2/5/2010
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
10