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LM3352 Regulated 200 mA Buck-Boost Switched Capacitor DC/DC Converter
June 1999
LM3352 Regulated 200 mA Buck-Boost Switched Capacitor DC/DC Converter
General Description
The LM3352 is a CMOS switched capacitor DC/DC converter that produces a regulated output voltage by automatically stepping up (boost) or stepping down (buck) the input voltage. It accepts an input voltage between 2.5V and 5.5V. The LM3352 is available in three standard output voltage versions: 2.5V, 3.0V and 3.3V. If other output voltage options between 1.8V and 4.0V are desired, please contact your National Semiconductor representative. The LM3352's proprietary buck-boost architecture enables up to 200 mA of load current at an average efficiency greater than 80%. Typical operating current is only 400 A and the typical shutdown current is only 2.5 A. The LM3352 is available in a 16-pin TSSOP package. This package has a maximum height of only 1.1 mm. The high efficiency of the LM3352, low operating and shutdown currents, small package size, and the small size of the overall solution make this device ideal for battery powered, portable, and hand-held applications. n Custom output voltages available from 1.8V to 4.0V in 100 mV increments n 2.5V to 5.5V input voltage n Up to 200 mA output current n >80% average efficiency n Uses few, low-cost external components n Very small solution size n 400 A typical operating current n 2.5 A typical shutdown current n 1 MHz switching frequency (typical) n Architecture and control methods provide high load current and good efficiency n TSSOP-16 package n Over-temperature protection
Applications
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 n 3.3V to 2.5V and 5.0V to 3.3V conversion
Features
n Regulated VOUT with 3% accuracy n Standard output voltage options: 2.5V, 3.0V and 3.3V
Typical Operating Circuit
DS101037-1
(c) 1999 National Semiconductor Corporation
DS101037
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Connection Diagram
DS101037-2
Top View TSSOP-16 Pin Package See NS Package Number MTC16
Ordering Information
Order Number LM3352MTCX-2.5 LM3352MTC-2.5 LM3352MTCX-3.0 LM3352MTC-3.0 LM3352MTCX-3.3 LM3352MTC-3.3 Package Type TSSOP-16 TSSOP-16 TSSOP-16 TSSOP-16 TSSOP-16 TSSOP-16 NSC Package Drawing MTC16 MTC16 MTC16 MTC16 MTC16 MTC16 Supplied As 2.5k Units, Tape and Reel 94 Units, Rail 2.5k Units, Tape and Reel 94 Units, Rail 2.5k Units, Tape and Reel 94 Units, Rail
Pin Description
Pin Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Name GND C3- C3+ C2- C2+ C1- C1+ VOUT GND VIN NC GND SD GND CFIL GND Ground* Negative Terminal for C3 Positive Terminal for C3 Negative Terminal for C2 Positive Terminal for C2 Negative Terminal for C1 Positive Terminal for C1 Regulated Output Voltage Ground* Input Supply Voltage This pin must be left unconnected. Ground* Active Low CMOS Logic-Level Shutdown Input Ground* Filter Capacitor; A 1 F ceramic capacitor is suggested. Ground* Function
*All GND pins of the LM3352 must be connected to the same ground.
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VOUT Pin All Other Pins Power Dissipation (TA = 25C) (Note 2) TJMAX (Note 2) JA (Note 2) Storage Temperature -0.5V to 4.5V -0.5V to 5.6V 700 mW 150C 150C/W -65C to +150C
Lead Temperature (Soldering, 5 sec.) ESD Rating (Note 3) human body model machine model
260C 2 kV 100V
Operating Ratings
Input Voltage (VIN ) Output Voltage (VOUT ) Ambient Temperature (TA ) (Note 2) Junction Temperature (T J) (Note 2) 2.5V to 5.5V 1.8V to 4.0V -40C to +85C -40C to +125C
Electrical Characteristics
Limits in standard typeface are for TJ = 25C, and limits in boldface type apply over the full operating temperature range. Unless otherwise specified: C1 = C2 = C3 = 0.33 F; CIN = 15 F; COUT = 33 F; VIN = 3.5V. Parameter LM3352-2.5 Output Voltage (V
OUT)
Conditions VIN = 3.5V; I = 100 mA
Min 2.463 2.425/2.400 2.425/2.400 2.425/2.400
Typ 2.5 2.5 2.5 2.5 85 75 75
Max 2.537 2.575/2.600 2.575/2.600 2.575/2.600
Units
LOAD
2.8V < VIN < 5.5V; 1 mA < ILOAD < 100 mA 3.6V < VIN < 4.9V; 1 mA < ILOAD < 200 mA 4.9V < VIN < 5.5V; 1 mA < ILOAD < 175 mA Efficiency Output Voltage Ripple (Peak-to-Peak) LM3352-3.0 Output Voltage (V
OUT)
V
ILOAD = 15 mA ILOAD = 150 mA, VIN = 4.0V ILOAD = 50 mA C OUT = 33 F tantalum VIN = 3.5V; I = 100 mA 2.955 2.910/2.880 2.910/2.880
% mVP-P
LOAD
3.0 3.0 3.0 80 75 75
3.045 3.090/3.120 3.090/3.120 % mVP-P V
2.5V < VIN < 5.5V; 1 mA < ILOAD < 100 mA 3.8V < VIN < 5.5V; 1 mA < ILOAD < 200 mA Efficiency Output Voltage Ripple (Peak-to-Peak) LM3352-3.3 Output Voltage (V
OUT)
ILOAD = 15 mA ILOAD = 150 mA, VIN = 4.0V ILOAD = 50 mA C OUT = 33 F tantalum VIN = 3.5V; I = 100 mA 3.251 3.201/3.168 3.201/3.168
LOAD
3.3 3.3 3.3 90 80 75
3.349 3.399/3.432 3.399/3.432 % mVP-P V
2.5V < VIN < 5.5V; 1 mA < ILOAD < 100 mA 4.0V < VIN < 5.5V; 1 mA < ILOAD < 200 mA Efficiency Output Voltage Ripple (Peak-to-Peak) Operating Quiescent Current Shutdown Quiescent Current Switching Frequency SD Input Threshold Low SD Input Threshold High 2.5V < VIN < 5.5V 2.5V < VIN < 5.5V
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ILOAD = 15 mA ILOAD = 150 mA, VIN = 4.0V ILOAD = 50 mA C OUT = 33 F tantalum Measured at Pin VIN; I LOAD = 0A (Note 4) SD Pin at 0V (Note 5) 0.65 0.8 VIN
LM3352-ALL OUTPUT VOLTAGE VERSIONS 400 2.5 1 500 5 1.35 0.2 VIN A A MHz V V
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Electrical Characteristics
Parameter
(Continued)
Limits in standard typeface are for TJ = 25C, and limits in boldface type apply over the full operating temperature range. Unless otherwise specified: C1 = C2 = C3 = 0.33 F; CIN = 15 F; COUT = 33 F; VIN = 3.5V. Conditions Measured at SD Pin; SD Pin = VIN = 5.5V Min Typ Max Units LM3352-ALL OUTPUT VOLTAGE VERSIONS SD Input Current 0.1 1.0 A
Note 1: "Absolute Maximum Ratings" indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device beyond its rated operating conditions. Note 2: As long as TA +85C, all electrical characteristics hold true for the 3.0V and 3.3V options at all current loads and the 2.5V option at all loads when VIN 5V. For VIN > 5V with the 2.5V option, the junction temperature rise above ambient is: T = 540IL-23 where IL is in amps. The output current must be derated at higher ambient temperatures to make sure TJ does not exceed 150C when operating the 2.5V option at VIN > 5V. Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 k resistor into each pin. The machine model is a 200 pF capacitor discharged directly into each pin. Note 4: The VOUT pin is forced to 200 mV above the typical VOUT. This is to insure that the internal switches are off. Note 5: The output capacitor COUT is fully discharged before measurement.
Typical Performance Characteristics
VOUT vs. VIN
Unless otherwise specified TA = 25C. VOUT vs. VIN
DS101037-4
DS101037-5
VOUT vs. VIN
VOUT vs. VIN
DS101037-6
DS101037-7
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Typical Performance Characteristics
VOUT vs. VIN
Unless otherwise specified TA = 25C. (Continued) VOUT vs. VIN
DS101037-8
DS101037-9
VOUT vs. VIN
VOUT vs. VIN
DS101037-10
DS101037-11
VOUT vs. VIN
Load Transient Response
DS101037-12
DS101037-14
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Typical Performance Characteristics
Efficiency vs. VIN
Unless otherwise specified TA = 25C. (Continued) Efficiency vs. VIN
DS101037-20
DS101037-21
Efficiency vs. VIN
Switching Frequency vs. VIN
DS101037-22
DS101037-23
Operating Quiescent Current vs. VIN
VOUT Ripple vs. COUT
DS101037-30 DS101037-24
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Typical Performance Characteristics
VOUT Ripple vs. COUT
Unless otherwise specified TA = 25C. (Continued) VOUT Ripple vs. COUT
DS101037-31
DS101037-32
Applications Information
DS101037-3
FIGURE 1. Block Diagram
Operating Principle
The LM3352 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 16-pin TSSOP package. The LM3352 can provide a regulated voltage between 1.8V and 4V from an input voltage between 2.5V and 5.5V. It can supply a load current up to 200 mA. As shown in Figure 1, the LM3352 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 seven
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gains based on inputs from the A/D and the comparator. The 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. Since efficiency is automatically optimized, the curves for VOUT vs. VIN and Efficiency vs. VIN in the Typical Performance 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 variations in output voltage and efficiency result. In all cases where these small variations are observed, the part is operating correctly; minimizing output voltage changes and optimizing efficiency.
Charge Pump Capacitor Selection
A 0.33 F ceramic capacitor is suggested for C1, C2 and C3. To ensure proper operation over temperature variations, an X7R dielectric material is recommended.
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Filter Capacitor Selection
a) CAPACITOR TECHNOLOGIES The three major technologies of capacitors that can be used as filter capacitors for LM3352 are: i) tantalum, ii) ceramic and iii) polymer electrolytic technologies. i) Tantalum Tantalum capacitors are widely used in switching regulators. Tantalum capacitors have the highest CV rating of any technology; as a result, high values of capacitance can be obtained in relatively small package sizes. It is also possible to obtain high value tantalum capacitors in very low profile (<1.2 mm) packages. This makes the tantalums attractive for low-profile, small size applications. Tantalums also possess very good temperature stability; i.e., the change in the capacitance value, and impedance over temperature is relatively 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 good, especially at high frequencies (>1 MHz). ii) Ceramic Ceramic capacitors have the lowest ESR of the three technologies and their frequency stability is exceptionally good. These characteristics make the ceramics an attractive
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 (>1 F) are achievable from companies such as Taiyo-yuden which are suitable for use with regulators. Ceramics are taller and larger than the tantalums of the same capacitance value. iii) Polymer Electrolytic 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 values. 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 (comparable to ceramics) and good temperature stability (comparable to tantalums). The Aluminum Polymer Electrolytics offered by Cornell-Dubilier and Panasonic, and the POSCAPs offered by Sanyo fall under this category.
Table 1 compares the features of the three capacitor technologies.
TABLE 1. Comparison of Capacitor Technologies Ceramic ESR Relative Height Relative Footprint Temperature Stability Frequency Stability VOUT Ripple Magnitude @ <50 mA VOUT Ripple Magnitude @ >100 mA dv/dt of VOUT Ripple @ All Loads b) CAPACITOR SELECTION i) Output Capacitor (COUT) The output capacitor COUT directly affects the magnitude of the output ripple voltage so COUT should be carefully selected. 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 electrolytics are a good choice for low ripple, low noise applications where size is less of a concern. Lowest Low for Small Values (<10 F); Taller for Higher Values Large X7R/X5R-Acceptable Good Low Low Lowest Tantalum High Lowest Small Good Acceptable High Slightly Higher High Polymer Electrolytic Low Low Largest Good Good Low Low Low
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 15 F polymer electrolytic, 22 F ceramic, or 33 F tantalum capacitor is recommended. This will ensure low input ripple at 200 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 ceramics 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 applications. The ceramics and polymer electrolytics are a good choice for low ripple, low noise applications where size is less of a concern. The 15 F polymer electrolytics are physically much larger than the 33 F tantalums and 22 F ceramics.
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Filter Capacitor Selection
iii) CFIL
(Continued)
Of the different capacitor technologies, a sample of vendors that have been verified as suitable for use with the LM3352 are shown in Table 2.
A 1 F, XR7 ceramic capacitor should be connected to pin CFIL. This capacitor provides the filtering needed for the internal supply rail of the LM3352. TABLE 2. Capacitor Vendor Information Manufacturer Ceramic Tantalum Polymer Electrolytic Taiyo-yuden AVX Sprague/Vishay Nichicon Cornell-Dubilier (ESRD) Sanyo (POSCAP) Tel (408) 573-4150 (803) 448-9411 (207) 324-4140 (847) 843-7500 (508) 996-8561 (619) 661-6322 Fax (408) 573-4159 (803) 448-1943 (207) 324-7223 (847) 843-2798 (508) 996-3830 (619) 661-1055 Website www.t-yuden.com www.avxcorp.com www.vishay.com www.nichicon.com www.cornell-dubilier.com www.sanyovideo.com
Maximum Available Output Current
The LM3352 cannot provide 200 mA under all VIN and VOUT conditions. The VOUT vs VIN graphs in the Typical Performance Characteristics section show the minimum VIN at which the LM3352 is capable of providing different load currents while maintaining VOUT regulation. Refer to the Electrical Characteristics for guaranteed conditions.
tion, any load up to the maximum as specified in the Electrical Characteristics may be applied. Using a Power On Reset circuit is recommended if greater start up loads are expected.
Thermal Protection
During output short circuit conditions, the LM3352 will draw high currents causing a rise in the junction temperature. On-chip thermal protection circuitry disables the charge 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.
Maximum Load Under Start-Up
Due to the LM3352's unique start-up sequence, it is not able to start up under all load conditions. Starting with 45 mA or less will allow the part to start correctly under any temperature or input voltage conditions. After the output is in regula-
Typical Application Circuits
DS101037-33
FIGURE 2. Basic Buck/Boost Regulator
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Typical Application Circuits
(Continued)
DS101037-15
FIGURE 3. Low Output Noise and Ripple Buck/Boost Regulator
Layout Considerations
Due to the 1 MHz typical switching frequency of the LM3352, careful board layout is a must. It is important to place the 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. Figure 4 shows a typical layout as used in the LM3352 evaluation board.
DS101037-16
FIGURE 4. Typical Layout, Top View (magnification 2.8X)
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LM3352 Regulated 200 mA Buck-Boost Switched Capacitor DC/DC Converter
Physical Dimensions
inches (millimeters) unless otherwise noted
TSSOP-16 Pin Package For Ordering, Refer to Ordering Information Table NS Package Number MTC16
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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

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