LM2681 LM2681 Switched Capacitor Voltage Converter Literature Number: SNVS042A LM2681 Switched Capacitor Voltage Converter General Description Features The LM2681 CMOS charge-pump voltage converter operates as a voltage doubler for an input voltage in the range of +2.5V to +5.5V. Two low cost capacitors and a diode (needed during start-up) is used in this circuit to provide up to 20 mA of output current. The LM2681 can also work as a voltage divider to split a voltage in the range of +1.8V to +11V in half. n n n n The LM2681 operates at 160 kHz oscillator frequency to reduce output resistance and voltage ripple. With an operating current of only 550 A (operating efficiency greater than 90% with most loads) the LM2681 provides ideal performance for battery powered systems. The device is in SOT23-6 package. n n n n n n Doubles or Splits Input Supply Voltage SOT23-6 Package 15 Typical Output Impedance 90% Typical Conversion Efficiency at 20 mA Applications Cellular Phones Pagers PDAs Operational Amplifier Power Suppliers Interface Power Suppliers Handheld Instruments Basic Application Circuits Voltage Doubler 10096501 Splitting Vin in Half 10096502 (c) 2003 National Semiconductor Corporation DS100965 www.national.com LM2681 Switched Capacitor Voltage Converter January 2003 LM2681 Absolute Maximum Ratings TJMax(Note 3) (Note 1) 150C If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. JA (Note 3) V+ to GND Voltage: Storage Temperature Range 5.8V OUT to GND Voltage: 11.6V OUT to V+ Voltage: Output Short-Circuit Duration to GND (Note 2) Continuous Power Dissipation (TA = 25C)(Note 3) -40 to 85C -65C to +150C Lead Temp. (Soldering, 10 seconds) 5.8V V+ and OUT Continuous Output Current 210C/W Operating Junction Temperature Range 300C ESD Rating 2kV 30 mA 1 sec. 600 mW 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: V+ = 5V, C1 = C2 = 3.3 F. (Note 4) Symbol Parameter V+ Supply Voltage IQ Supply Current Condition Min Typ Max 5.5 V 550 1000 A 2.5 No Load Units IL Output Current RSW Sum of the Rds(on)of the four internal MOSFET switches ROUT Output Resistance (Note 5) IL = 20 mA fOSC Oscillator Frequency (Note 6) 80 160 kHz fSW Switching Frequency (Note 6) 40 80 kHz PEFF Power Efficiency RL (1.0k) between GND and OUT 86 93 20 IL = 20 mA IL = 20 mA to GND VOEFF Voltage Conversion Efficiency No Load mA 8 16 15 40 % 90 99 99.96 % 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: OUT may be shorted to GND for one second without damage. However, shorting OUT to V+ may damage the device and should be avoided. Also, for temperatures above 85C, OUT must not be shorted to GND or V+, or device may be damaged. Note 3: The maximum allowable power dissipation is calculated by using PDMax = (TJMax - TA)/JA, where TJMax is the maximum junction temperature, TA is the ambient temperature, and JA is the junction-to-ambient thermal resistance of the specified package. Note 4: In the test circuit, capacitors C1 and C2 are 3.3 F, 0.3 maximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce output voltage and efficiency. Note 5: Specified output resistance includes internal switch resistance and capacitor ESR. See the details in the application information for positive voltage doubler. Note 6: The output switches operate at one half of the oscillator frequency, fOSC = 2fSW. www.national.com 2 LM2681 Test Circuit 10096503 FIGURE 1. LM2681 Test Circuit Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified) Supply Current vs Supply Voltage Supply Current vs Temperature 10096505 10096504 Output Source Resistance vs Supply Voltage Output Source Resistance vs Temperature 10096507 10096506 3 www.national.com LM2681 Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified) (Continued) Output Voltage Drop vs Load Current Efficiency vs Load Current 10096508 10096509 Oscillator Frequency vs Supply Voltage Oscillator Frequency vs Temperature 10096510 10096511 Connection Diagram 6-Lead SOT (M6) 10096522 Actual Size 10096513 Top View With Package Marking Ordering Information Order Number Package Number Package Marking LM2681M6 MA06A S10A (Note 7) Tape and Reel (250 units/rail) Supplied as LM2681M6X MA06A S10A (Note 7) Tape and Reel (3000 units/rail) Note 7: The first letter "S" identifies the part as a switched capacitor converter. The next two numbers are the device number. The fourth letter "A" indicates the grade. Only one grade is available. Larger quantity reels are available upon request. www.national.com 4 LM2681 Pin Description Function Pin Name 1 V+ 2 Voltage Doubler Voltage Split Power supply positive voltage input Positive voltage output GND Power supply ground input Same as doubler 3 CAP- Connect this pin to the negative terminal of the charge-pump capacitor Same as doubler 4 GND Power supply ground input Same as doubler 5 OUT Positive voltage output Power supply positive voltage input 6 CAP+ Connect this pin to the positive terminal of the charge-pump capacitor Same as doubler mately equal to the output current, therefore, its ESR only counts once in the output resistance. A good approximation of Rout is: Circuit Description The LM2681 contains four large CMOS switches which are switched in a sequence to double the input supply voltage. Energy transfer and storage are provided by external capacitors. Figure 2 illustrates the voltage conversion scheme. When S2 and S4 are closed, C1 charges to the supply voltage V+. During this time interval, switches S1 and S3 are open. In the next time interval, S2 and S4 are open; at the same time, S1 and S3 are closed, the sum of the input voltage V+ and the voltage across C1 gives the 2V+ output voltage when there is no load. The output voltage drop when a load is added is determined by the parasitic resistance (Rds(on) of the MOSFET switches and the ESR of the capacitors) and the charge transfer loss between capacitors. Details will be discussed in the following application information section. where RSW is the sum of the ON resistance of the internal MOSFET switches shown in Figure 2. The peak-to-peak output voltage ripple is determined by the oscillator frequency, the capacitance and ESR of the output capacitor C2: High capacitance, low ESR capacitors can reduce both the output reslistance and the voltage ripple. The Schottky diode D1 is only needed for start-up. The internal oscillator circuit uses the OUT pin and the GND pin. Voltage across OUT and GND must be larger than 1.8V to insure the operation of the oscillator. During start-up, D1 is used to charge up the voltage at the OUT pin to start the oscillator; also, it protects the device from turning-on its own parasitic diode and potentially latching-up. Therefore, the Schottky diode D1 should have enough current carrying capability to charge the output capacitor at start-up, as well as a low forward voltage to prevent the internal parasitic diode from turning-on. A Schottky diode like 1N5817 can be used for most applications. If the input voltage ramp is less than 10V/ms, a smaller Schottky diode like MBR0520LT1 can be used to reduce the circuit size. 10096514 FIGURE 2. Voltage Doubling Principle SPLIT V+ IN HALF Another interesting application shown in the Basic Application Circuits is using the LM2681 as a precision voltage divider. . This circuit can be derived from the voltage doubler by switching the input and output connections. In the voltage divider, the input voltage applies across the OUT pin and the GND pin (which are the power rails for the internal oscillator), therefore no start-up diode is needed. Also, since the offvoltage across each switch equals Vin/2, the input voltage can be raised to +11V. Application Information POSITIVE VOLTAGE DOUBLER The main application of the LM2681 is to double the input voltage. The range of the input supply voltage is 2.5V to 5.5V. The output characteristics of this circuit can be approximated by an ideal voltage source in series with a resistance. The voltage source equals 2V+. The output resistance Rout is a function of the ON resistance of the internal MOSFET switches, the oscillator frequency, the capacitance and ESR of C1 and C2. Since the switching current charging and discharging C1 is approximately twice as the output current, the effect of the ESR of the pumping capacitor C1 will be multiplied by four in the output resistance. The output capacitor C2 is charging and discharging at a current approxi5 www.national.com LM2681 Application Information CAPACITOR SELECTION Where IQ(V+) is the quiescent power loss of the IC device, and IL2Rout is the conversion loss associated with the switch on-resistance, the two external capacitors and their ESRs. As discussed in the Positive Voltage Doubler section, the output resistance and ripple voltage are dependent on the capacitance and ESR values of the external capacitors. The output voltage drop is the load current times the output resistance, and the power efficiency is The selection of capacitors is based on the specifications of the dropout voltage (which equals Iout Rout), the output voltage ripple, and the converter efficiency. Low ESR capacitors (Table 1) are recommended to maximize efficiency, reduce the output voltage drop and voltage ripple. (Continued) Low ESR Capacitor Manufacturers Manufacturer Phone Capacitor Type Nichicon Corp. (708)-843-7500 PL & PF series, through-hole aluminum electrolytic AVX Corp. (803)-448-9411 TPS series, surface-mount tantalum Sprague (207)-324-4140 593D, 594D, 595D series, surface-mount tantalum Sanyo (619)-661-6835 OS-CON series, through-hole aluminum electrolytic Murata (800)-831-9172 Ceramic chip capacitors Taiyo Yuden (800)-348-2496 Ceramic chip capacitors Tokin (408)-432-8020 Ceramic chip capacitors Other Applications PARALLELING DEVICES Any number of LM2681s can be paralleled to reduce the output resistance. Each device must have its own pumping capacitor C1, while only one output capacitor Cout is needed as shown in Figure 3. The composite output resistance is: 10096519 FIGURE 3. Lowering Output Resistance by Paralleling Devices CASCADING DEVICES Cascading the LM2681s is an easy way to produce a greater voltage (A two-stage cascade circuit is shown in Figure 4). The effective output resistance is equal to the weighted sum of each individual device: www.national.com Rout = 1.5Rout_1 + Rout_2 Note that, the increasing of the number of cascading stages is pracitically limited since it significantly reduces the efficiency, increases the output resistnace and output voltage ripple. 6 LM2681 Other Applications (Continued) 10096520 FIGURE 4. Increasing Output Voltage by Cascading Devices Note that, the following conditions must be satisfied simultaneously for worst case design: 2Vin_min > Vout_min +Vdrop_max (LP2980) + Iout_max x Rout_max (LM2681) 2Vin_max < Vout_max +Vdrop_min (LP2980) + Iout_min x Rout_min (LM2681) REGULATING VOUT It is possible to regulate the output of the LM2681 by use of a low dropout regulator (such as LP2980-5.0). The whole converter is depicted in Figure 5. A different output voltage is possible by use of LP2980-3.3, LP2980-3.0, or LP2980-adj. 10096521 FIGURE 5. Generate a Regulated +5V from +3V Input Voltage 7 www.national.com LM2681 Switched Capacitor Voltage Converter Physical Dimensions inches (millimeters) unless otherwise noted 6-Lead Small Outline Package (M6) NS Package Number MA06A For Order Numbers, refer to the table in the "Ordering Information" section of this document. LIFE SUPPORT POLICY NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Americas Customer Support Center Email: new.feedback@nsc.com Tel: 1-800-272-9959 www.national.com National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Francais Tel: +33 (0) 1 41 91 8790 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Asia Pacific Customer Support Center Fax: 65-6250 4466 Email: ap.support@nsc.com Tel: 65-6254 4466 National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: nsj.crc@jksmtp.nsc.com Tel: 81-3-5639-7560 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. IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI's terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI's standard warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by government requirements, testing of all parameters of each product is not necessarily performed. TI assumes no liability for applications assistance or customer product design. Customers are responsible for their products and applications using TI components. To minimize the risks associated with customer products and applications, customers should provide adequate design and operating safeguards. TI does not warrant or represent that any license, either express or implied, is granted under any TI patent right, copyright, mask work right, or other TI intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information published by TI regarding third-party products or services does not constitute a license from TI to use such products or services or a warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the third party, or a license from TI under the patents or other intellectual property of TI. Reproduction of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied by all associated warranties, conditions, limitations, and notices. Reproduction of this information with alteration is an unfair and deceptive business practice. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional restrictions. Resale of TI products or services with statements different from or beyond the parameters stated by TI for that product or service voids all express and any implied warranties for the associated TI product or service and is an unfair and deceptive business practice. TI is not responsible or liable for any such statements. TI products are not authorized for use in safety-critical applications (such as life support) where a failure of the TI product would reasonably be expected to cause severe personal injury or death, unless officers of the parties have executed an agreement specifically governing such use. Buyers represent that they have all necessary expertise in the safety and regulatory ramifications of their applications, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any use of TI products in such safety-critical applications, notwithstanding any applications-related information or support that may be provided by TI. Further, Buyers must fully indemnify TI and its representatives against any damages arising out of the use of TI products in such safety-critical applications. TI products are neither designed nor intended for use in military/aerospace applications or environments unless the TI products are specifically designated by TI as military-grade or "enhanced plastic." Only products designated by TI as military-grade meet military specifications. Buyers acknowledge and agree that any such use of TI products which TI has not designated as military-grade is solely at the Buyer's risk, and that they are solely responsible for compliance with all legal and regulatory requirements in connection with such use. TI products are neither designed nor intended for use in automotive applications or environments unless the specific TI products are designated by TI as compliant with ISO/TS 16949 requirements. Buyers acknowledge and agree that, if they use any non-designated products in automotive applications, TI will not be responsible for any failure to meet such requirements. Following are URLs where you can obtain information on other Texas Instruments products and application solutions: Products Applications Audio www.ti.com/audio Communications and Telecom www.ti.com/communications Amplifiers amplifier.ti.com Computers and Peripherals www.ti.com/computers Data Converters dataconverter.ti.com Consumer Electronics www.ti.com/consumer-apps DLP(R) Products www.dlp.com Energy and Lighting www.ti.com/energy DSP dsp.ti.com Industrial www.ti.com/industrial Clocks and Timers www.ti.com/clocks Medical www.ti.com/medical Interface interface.ti.com Security www.ti.com/security Logic logic.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense Power Mgmt power.ti.com Transportation and Automotive www.ti.com/automotive Microcontrollers microcontroller.ti.com Video and Imaging RFID www.ti-rfid.com OMAP Mobile Processors www.ti.com/omap Wireless Connectivity www.ti.com/wirelessconnectivity TI E2E Community Home Page www.ti.com/video e2e.ti.com Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265 Copyright (c) 2011, Texas Instruments Incorporated