LM2681 www.ti.com SNVS042B - MARCH 1999 - REVISED MAY 2013 LM2681 Switched Capacitor Voltage Converter Check for Samples: LM2681 FEATURES DESCRIPTION * * * * 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. 1 2 Doubles or Splits Input Supply Voltage SOT-23 6-Lead 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 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 a SOT-23, 6-lead package. Basic Application Circuits Voltage Doubler Splitting Vin in Half 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright (c) 1999-2013, Texas Instruments Incorporated LM2681 SNVS042B - MARCH 1999 - REVISED MAY 2013 www.ti.com These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. Absolute Maximum Ratings (1) (2) V+ to GND Voltage 5.8V OUT to GND Voltage 11.6V OUT to V+ Voltage 5.8V V+ and OUT Continuous Output Current 30 mA Output Short-Circuit Duration to GND (3) 1 sec. Continuous Power Dissipation (TA = 25C) (4) 600 mW TJMax (4) 150C JA (4) 210C/W -40 to 85C Operating Junction Temperature Range -65C to +150C Storage Temperature Range Lead Temp. (Soldering, 10 seconds) 300C ESD Rating (1) 2kV 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. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and specifications. 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. 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. (2) (3) (4) 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. (1) Symbol Parameter V+ Supply Voltage IQ Supply Current IL Output Current RSW Sum of the Rds(on)of the four internal MOSFET switches ROUT Output Resistance Condition Min Typ Max 5.5 V 550 1000 A 2.5 No Load 20 (2) Units mA IL = 20 mA 8 16 IL = 20 mA 15 40 (3) fOSC Oscillator Frequency See 80 160 kHz fSW Switching Frequency See (3) 40 80 kHz PEFF Power Efficiency RL (1.0k) between GND and OUT 86 93 IL = 20 mA to GND VOEFF (1) (2) (3) 2 Voltage Conversion Efficiency No Load 90 99 99.96 % % 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. Specified output resistance includes internal switch resistance and capacitor ESR. See POSITIVE VOLTAGE DOUBLER The output switches operate at one half of the oscillator frequency, fOSC = 2fSW. Submit Documentation Feedback Copyright (c) 1999-2013, Texas Instruments Incorporated Product Folder Links: LM2681 LM2681 www.ti.com SNVS042B - MARCH 1999 - REVISED MAY 2013 Test Circuit Figure 1. LM2681 Test Circuit Submit Documentation Feedback Copyright (c) 1999-2013, Texas Instruments Incorporated Product Folder Links: LM2681 3 LM2681 SNVS042B - MARCH 1999 - REVISED MAY 2013 www.ti.com Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified) 4 Supply Current vs Supply Voltage Supply Current vs Temperature Figure 2. Figure 3. Output Source Resistance vs Supply Voltage Output Source Resistance vs Temperature Figure 4. Figure 5. Output Voltage Drop vs Load Current Efficiency vs Load Current Figure 6. Figure 7. Submit Documentation Feedback Copyright (c) 1999-2013, Texas Instruments Incorporated Product Folder Links: LM2681 LM2681 www.ti.com SNVS042B - MARCH 1999 - REVISED MAY 2013 Typical Performance Characteristics (continued) (Circuit of Figure 1, V+ = 5V unless otherwise specified) Oscillator Frequency vs Supply Voltage Oscillator Frequency vs Temperature Figure 8. Figure 9. Submit Documentation Feedback Copyright (c) 1999-2013, Texas Instruments Incorporated Product Folder Links: LM2681 5 LM2681 SNVS042B - MARCH 1999 - REVISED MAY 2013 www.ti.com CONNECTION DIAGRAM Figure 10. SOT-23, 6-Lead Package - Top View See Package Number DBV Figure 11. Actual Size PIN DESCRIPTION Pin Name 1 V+ 2 Function 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 chargepump 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 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 12 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 APPLICATION INFORMATION section. Figure 12. Voltage Doubling Principle 6 Submit Documentation Feedback Copyright (c) 1999-2013, Texas Instruments Incorporated Product Folder Links: LM2681 LM2681 www.ti.com SNVS042B - MARCH 1999 - REVISED MAY 2013 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 approximately equal to the output current, therefore, its ESR only counts once in the output resistance. A good approximation of Rout is: (1) where RSW is the sum of the ON resistance of the internal MOSFET switches shown in Figure 12. The peak-to-peak output voltage ripple is determined by the oscillator frequency, the capacitance and ESR of the output capacitor C2: (2) 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 startup, 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. 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 off-voltage across each switch equals Vin/2, the input voltage can be raised to +11V. CAPACITOR SELECTION 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 (3) IL2Rout Where IQ(V+) is the quiescent power loss of the IC device, and switch on-resistance, the two external capacitors and their ESRs. is the conversion loss associated with the 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 are recommended to maximize efficiency, reduce the output voltage drop and voltage ripple. Submit Documentation Feedback Copyright (c) 1999-2013, Texas Instruments Incorporated Product Folder Links: LM2681 7 LM2681 SNVS042B - MARCH 1999 - REVISED MAY 2013 www.ti.com 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 13. The composite output resistance is: (4) Figure 13. 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 14). The effective output resistance is equal to the weighted sum of each individual device: Rout = 1.5Rout_1 + Rout_2 (5) Note that, the increasing of the number of cascading stages is practically limited since it significantly reduces the efficiency, increases the output resistance and output voltage ripple. Figure 14. Increasing Output Voltage by Cascading Devices 8 Submit Documentation Feedback Copyright (c) 1999-2013, Texas Instruments Incorporated Product Folder Links: LM2681 LM2681 www.ti.com SNVS042B - MARCH 1999 - REVISED MAY 2013 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 15. A different output voltage is possible by use of LP2980-3.3, LP2980-3.0, or LP2980-adj. 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) (6) (7) Figure 15. Generate a Regulated +5V from +3V Input Voltage Submit Documentation Feedback Copyright (c) 1999-2013, Texas Instruments Incorporated Product Folder Links: LM2681 9 LM2681 SNVS042B - MARCH 1999 - REVISED MAY 2013 www.ti.com REVISION HISTORY Changes from Revision A (May 2013) to Revision B * 10 Page Changed layout of National Data Sheet to TI format ............................................................................................................ 9 Submit Documentation Feedback Copyright (c) 1999-2013, Texas Instruments Incorporated Product Folder Links: LM2681 PACKAGE OPTION ADDENDUM www.ti.com 4-Nov-2016 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Op Temp (C) Device Marking (4/5) LM2681M6/NOPB ACTIVE SOT-23 DBV 6 1000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 85 S10A LM2681M6X/NOPB ACTIVE SOT-23 DBV 6 3000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 85 S10A (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. 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Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 20-Dec-2016 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) LM2681M6/NOPB SOT-23 DBV 6 1000 178.0 8.4 LM2681M6X/NOPB SOT-23 DBV 6 3000 178.0 8.4 Pack Materials-Page 1 B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant 3.2 3.2 1.4 4.0 8.0 Q3 3.2 3.2 1.4 4.0 8.0 Q3 PACKAGE MATERIALS INFORMATION www.ti.com 20-Dec-2016 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM2681M6/NOPB SOT-23 DBV 6 1000 210.0 185.0 35.0 LM2681M6X/NOPB SOT-23 DBV 6 3000 210.0 185.0 35.0 Pack Materials-Page 2 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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