LM3355 [NSC]
Regulated 50mA Buck-Boost Switched Capacitor DC/DC Converter; 稳压50mA的降压 - 升压型开关电容DC / DC转换器
| 型号： | LM3355 |
| 厂家： | 
National Semiconductor |
| 描述： | Regulated 50mA Buck-Boost Switched Capacitor DC/DC Converter |
| 文件： | 总9页 (文件大小：182K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
December 2001
LM3355
Regulated 50mA Buck-Boost Switched Capacitor DC/DC
Converter
General Description
Features
±
n Regulated VOUT with 3% accuracy
n Standard output voltage of 4.1V
n Custom output voltages available from 1.8V to 4.1V in
100 mV increments
The LM3355 is a CMOS switched capacitor DC/DC con-
verter that produces a regulated output voltage by automati-
cally stepping up (boost) or stepping down (buck) the input
voltage. It accepts an input voltage between 2.5V and 5.5V.
The LM3355 is available with a standard output voltage of
4.1V (ideal for white LED applications). If other output volt-
age options between 1.8V and 4.1V are desired for other
applications, please contact your National Semiconductor
representative.
n 2.5V to 5.5V input voltage
n Up to 50 mA output current
>
n
75% average efficiency
n Uses few, low-cost external components
n Very small solution size
The LM3355’s proprietary buck-boost architecture enables
up to 50 mA of load current at an average efficiency greater
than 75%. Typical operating current is only 375 µA and the
typical shutdown current is only 2.3 µA.
n 375 µA typical operating current
n 2.3 µA typical shutdown current
n 1 MHz switching frequency (typical)
n Architecture and control methods provide high load
current and good efficiency
The LM3355 is available in a 10-pin MSOP package. This
package has a maximum height of only 1.1 mm.
n MSOP-10 package
n Over-temperature protection
The high efficiency of the LM3355, low operating and shut-
down currents, small package size, and the small size of the
overall solution make this device ideal for battery powered,
portable, and hand-held applications.
Applications
n White LED display backlights
See the LM3352 for up to 200mA of output current.
n 1-cell Lilon battery-operated equipment including PDAs,
hand-held PCs, cellular phones
n Flat panel displays
n Hand-held instruments
n NiCd, NiMH, or alkaline battery powered systems
Typical Operating Circuit
DS200219-1
© 2001 National Semiconductor Corporation
DS200219
www.national.com
Connection Diagram
DS200219-2
Top View
MSOP-10 Pin Package
See NS Package Number MUB10A
Ordering Information
Order Number
LM3355MMX-4.1
LM3355MM-4.1
Package Type
NSC Package Drawing
MUB10A
Supplied As
MSOP-10
MSOP-10
3.5k Units, Tape and Reel
1k Units, Tape and Reel
MUB10A
Pin Description
Pin Number
Name
Function
Input Supply Voltage
Negative Terminal for C1
Positive Terminal for C1
Ground
1
2
VIN
C1−
C1+
GND
GND
CFIL
SD
3
4
5
Ground
6
Filter Capacitor, a 1µF capacitor is recommended.
Shutdown, active low
7
8
VOUT
C2−
C2+
Regulated Output Voltage
9
Negative Terminal for C2
10
Positive Terminal for C2
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2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
ESD Rating (Note 3)
Human Body Model
Machine Model
1.5 kV
100V
Operating Ratings
All Pins
−0.5V to 5.6V
Input Voltage (VIN
Output Voltage (VOUT
Ambient Temperature (TA) (Note 2)
Junction Temperature (T ) (Note 2)
)
2.5V to 5.5V
1.8V to 4.1V
Power Dissipation (TA = 25˚C)
(Note 2)
)
Internally Limited
150˚C
−40˚C to +85˚C
−40˚C to +125˚C
TJMAX (Note 2)
θJA (Note 2)
250˚C/W
J
Storage Temperature
Lead Temperature (Soldering, 5 sec.)
−65˚C to +150˚C
260˚C
Electrical Characteristics
Limits in standard typeface are for TA = 25˚C, and limits in boldface type apply over the full operating temperature range of
−40˚C ≤ TA ≤ 85˚C. Unless otherwise specified: C1 = C2 = 0.33 µF; CIN = 10 µF; COUT = 10 µF; CFIL = 1 µF; VIN = 3.5V.
Parameter
LM3355-4.1
Output Voltage (V
Conditions
Min (Note 5)
Typ (Note 4)
Max (Note 5)
Units
)
VIN = 3.5V; I
= 50 mA
LOAD
4.038
4.1
4.1
4.162
OUT
<
<
<
2.6V VIN 5.5V;
3.977/3.936
4.223/4.264
<
1 mA ILOAD 50 mA
V
<
<
2.5V VIN 5.5V;
3.977/3.936
4.1
4.223/4.264
<
<
1 mA ILOAD 40 mA
Efficiency
ILOAD = 10 mA
80
75
%
ILOAD= 50 mA
Output Voltage Ripple
(Peak-to-Peak)
ILOAD = 50 mA
75
mVP-P
C
= 10 µF ceramic
OUT
LM3355-ALL OUTPUT VOLTAGE VERSIONS
Operating Quiescent Current
Measured at Pin VIN
;
375
475
µA
I
= 0A (Note 6)
LOAD
Shutdown Quiescent Current
Switching Frequency
SD Pin at 0V (Note 7)
2.3
1
5
µA
MHz
V
0.60
1.40
<
<
SD Input Threshold Low
SD Input Threshold High
SD Input Current
2.5V VIN 5.5V
0.2 VIN
<
<
2.5V VIN 5.5V
0.8 VIN
V
Measured at SD Pin;
SD Pin = VIN = 5.5V
0.3
µA
Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur. Operating Ratings are conditions for which the device is
intended to be functional, but device parameter specifications may not be guaranteed. For guaranteed specifications and test conditions, see “Electrical
Characteristics”.
Note 2: As long as T ≤ +85˚C, all electrical characteristics hold true and the junction temperature should remain below +125˚C.
A
Note 3: The Human Body Model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The Machine Model is a 200 pF capacitor discharged
directly into each pin.
Note 4: Typical numbers are at 25˚C and represent the most likely norm.
Note 5: All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are 100% tested
or guaranteed through statistical analysis. All limits at temperature extremes are guaranteed by correlation using standard Statistical Quality Control methods (SQC).
All limits are used to calculate Average Outgoing Quality Level (AOQL).
Note 6: The V
pin is forced to 200 mV above the typical V
. This is to insure that the internal switches are off.
OUT
OUT
Note 7: The output capacitor C
is fully discharged before measurement.
OUT
3
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Typical Performance Characteristics Unless otherwise specified TA = 25˚C.
VOUT vs. VIN
VOUT vs. VIN
DS200219-4
DS200219-5
Efficiency vs. VIN
Load Transient Response
DS200219-14
DS200219-20
Operating Quiescent
Current vs. VIN
Switching Frequency vs. VIN
DS200219-23
DS200219-24
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4
Typical Performance Characteristics Unless otherwise specified TA = 25˚C. (Continued)
Maximum VOUT Ripple vs. COUT
Maximum VOUT Ripple vs. COUT
DS200219-32
DS200219-30
Applications Information
DS200219-3
FIGURE 1. Block Diagram
gain signal is sent to the phase generator which then sends
the appropriate timing and configuration signals to the switch
array. This dual loop provides regulation over a wide range of
loads efficiently.
Operating Principle
The LM3355 is designed to provide a step-up/step-down
voltage regulation in battery powered systems. It combines
switched capacitor circuitry, reference, comparator, and
shutdown logic in a single 10-pin MSOP package. The
LM3355 can provide a regulated voltage between 1.8V and
4.1V from an input voltage between 2.5V and 5.5V. It can
supply a load current up to 50 mA.
Since efficiency is automatically optimized, the curves for
VOUT vs. VIN and Efficiency vs. VIN in the Typical Perfor-
mance Characteristics section exhibit small variations. The
reason is that as input voltage or output load changes, the
digital control loops are making decisions on how to optimize
efficiency. As the switch array is reconfigured, small varia-
tions in output voltage and efficiency result. In all cases
where these small variations are observed, the part is oper-
ating correctly; minimizing output voltage changes and opti-
mizing efficiency.
As shown in Figure 1, the LM3355 employs two feedback
loops to provide regulation in the most efficient manner
possible. The first loop is from VOUT through the comparator
COMP, the AND gate G1, the phase generator, and the
switch array. The comparator’s output is high when VOUT is
less than the reference VREF. Regulation is provided by
gating the clock to the switch array. In this manner, charge is
transferred to the output only when needed. The second
loop controls the gain configuration of the switch array. This
loop consists of the comparator, the digital control block, the
phase generator, and the switch array. The digital control
block computes the most efficient gain from a set of five
gains based on inputs from the A/D and the comparator. The
Charge Pump Capacitor Selection
A 0.33 µF ceramic capacitor is suggested for C1 and C2. To
ensure proper operation over temperature variations, an
X7R dielectric material is recommended.
5
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choice for low ripple, high frequency applications. However,
the temperature stability of the ceramics is bad, except for
the X7R and X5R dielectric types. High capacitance values
Filter Capacitor Selection
a) CAPACITOR TECHNOLOGIES
>
(
1
µF) are achievable from companies such as
The three major technologies of capacitors that can be used
as filter capacitors for LM3355 are: i) tantalum, ii) ceramic
and iii) polymer electrolytic technologies.
Taiyo-yuden which are suitable for use with regulators. Ce-
ramics are taller and larger than the tantalums of the same
capacitance value.
i) Tantalum
iii) Polymer Electrolytic
Tantalum capacitors are widely used in switching regulators.
Tantalum capacitors have the highest CV rating of any tech-
nology; as a result, high values of capacitance can be ob-
tained in relatively small package sizes. It is also possible to
obtain high value tantalum capacitors in very low profile
Polymer electrolytic is a third suitable technology. Polymer
capacitors provide some of the best features of both the
ceramic and the tantalum technologies. They provide very
low ESR values while still achieving high capacitance val-
ues. However, their ESR is still higher than the ceramics,
and their capacitance value is lower than the tantalums of
the same size. Polymers offer good frequency stability (com-
parable to ceramics) and good temperature stability (compa-
rable to tantalums). The Aluminum Polymer Electrolytics
offered by Cornell-Dubilier and Panasonic, and the POS-
CAPs offered by Sanyo fall under this category.
<
(
1.2 mm) packages. This makes the tantalums attractive
for low-profile, small size applications. Tantalums also pos-
sess very good temperature stability; i.e., the change in the
capacitance value, and impedance over temperature is rela-
tively small. However, the tantalum capacitors have relatively
high ESR values which can lead to higher voltage ripple and
their frequency stability (variation over frequency) is not very
Table 1 compares the features of the three capacitor tech-
nologies.
>
good, especially at high frequencies ( 1 MHz).
ii) Ceramic
Ceramic capacitors have the lowest ESR of the three tech-
nologies and their frequency stability is exceptionally good.
These characteristics make the ceramics an attractive
TABLE 1. Comparison of Capacitor Technologies
Polymer
Ceramic
Tantalum
High
Electrolytic
ESR
Lowest
Low
<
Relative Height
Low for Small Values ( 10 µF); Taller for
Lowest
Low
Higher Values
Relative Footprint
Large
Small
Largest
Good
Good
Low
Temperature Stability
Frequency Stability
VOUT Ripple Magnitude
VOUT Ripple Magnitude
X7R/X5R-Acceptable
Good
Good
Low
Acceptable
High
<
>
@
@
50 mA
100 mA
Low
Slightly Higher
High
Low
@
dv/dt of VOUT Ripple All Loads
Lowest
Low
b) CAPACITOR SELECTION
ii) Input Capacitor (CIN
)
The input capacitor CIN directly affects the magnitude of the
input ripple voltage, and to a lesser degree the VOUT ripple.
A higher value CIN will give a lower VIN ripple. To optimize
low input and output ripple as well as size a 10 µF polymer
electrolytic or ceramic, or 15 µF tantalum capacitor is rec-
ommended. This will ensure low input ripple at 50 mA load
current. If lower currents will be used or higher input ripple
can be tolerated then a smaller capacitor may be used to
reduce the overall size of the circuit. The lower ESR ceram-
ics and polymer electrolytics achieve a lower VIN ripple than
the higher ESR tantalums of the same value. Tantalums
make a good choice for small size, very low profile applica-
tions. The ceramics and polymer electrolytics are a good
choice for low ripple, low noise applications where size is
less of a concern. The 10 µF polymer electrolytics are physi-
cally much larger than the 15 µF tantalums and 10 µF
ceramics.
i) Output Capacitor (COUT
)
The output capacitor COUT directly affects the magnitude of
the output ripple voltage so COUT should be carefully se-
lected. The graphs titled VOUT Ripple vs. COUT in the Typical
Performance Characteristics section show how the ripple
voltage magnitude is affected by the COUT value and the
capacitor technology. These graphs are taken at the gain at
which worst case ripple is observed. In general, the higher
the value of COUT, the lower the output ripple magnitude. At
lighter loads, the low ESR ceramics offer a much lower VOUT
ripple than the higher ESR tantalums of the same value. At
higher loads, the ceramics offer a slightly lower VOUT ripple
magnitude than the tantalums of the same value. However,
the dv/dt of the VOUT ripple with the ceramics and polymer
electrolytics is much lower than the tantalums under all load
conditions. The tantalums are suggested for very low profile,
small size applications. The ceramics and polymer electro-
lytics are a good choice for low ripple, low noise applications
where size is less of a concern.
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6
Of the different capacitor technologies, a sample of vendors
that have been verified as suitable for use with the LM3355
are shown in Table 2.
Filter Capacitor Selection (Continued)
iii) CFIL
A 1 µF, X7R ceramic capacitor should be connected to pin
CFIL. This capacitor provides the filtering needed for the
internal supply rail of the LM3355.
TABLE 2. Capacitor Vendor Information
Manufacturer
Tel
Fax
Website
www.t-yuden.com
www.avxcorp.com
www.vishay.com
Ceramic
Taiyo-yuden
AVX
(408) 573-4150
(803) 448-9411
(207) 324-4140
(408) 573-4159
(803) 448-1943
(207) 324-7223
Sprague/Vishay
Tantalum
Nichicon
(847) 843-7500
(508) 996-8561
(619) 661-6322
(847) 843-2798
(508) 996-3830
(619) 661-1055
www.nichicon.com
Polymer Electrolytic
Cornell-Dubilier (ESRD)
Sanyo (POSCAP)
www.cornell-dubilier.com
www.sanyovideo.com
pump action once the junction temperature exceeds the
thermal trip point, and re-enables the charge pump when the
junction temperature falls back to a safe operating point.
Thermal Protection
During output short circuit conditions, the LM3355 will draw
high currents causing a rise in the junction temperature.
On-chip thermal protection circuitry disables the charge
Typical Application Circuits
DS200219-33
FIGURE 2. Basic Buck/Boost Regulator
DS200219-15
FIGURE 3. Low Output Noise and Ripple Buck/Boost Regulator
7
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capacitors as close to the IC as possible and to keep the
traces between the capacitors and the IC short and direct.
Use of a ground plane is recommended.
Layout Considerations
Due to the 1 MHz typical switching frequency of the LM3355,
careful board layout is a must. It is important to place the
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8
Physical Dimensions inches (millimeters) unless otherwise noted
MSOP-10 Pin Package (MM)
For Ordering, Refer to Ordering Information Table
NS Package Number MUB10A
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